[
{
"content": "see also [principles](https://gingkoapp.com/principles-of-ham-radio) and [basic](https://gingkoapp.com/basic-question-bank)\n\n[practice exam](https://apc-cap.ic.gc.ca/pls/apc_anon/apeg_practice.practice_form?p_level_id=1)"
},
{
"content": "' Questions Advanced.txt 2014 03 Copyright VE2AAY.",
"children": [
{
"content": "'\n' If you reproduce this without asking permission and giving due credit, may your CQ calls go forever unanswered.\n'\n' Sequence of questions is immaterial. They have been regrouped here under arbitrary \"Lessons\" used by the author.\n'\n' 2014 06 14 Tweak 3-2-4.\n'\n' Header format: ^ Qualification ^ Number of Questions ^ Pass Mark ^Designation of first Answer record^\n\n^ Advanced Qualification ^ 50 ^ 70 ^A\t^"
}
]
},
{
"content": "{L02} Inductors and Capacitors; resonant circuits",
"children": [
{
"content": "Upon the application or removal of voltage, the RC or RL time constant `tau` describes the changing rate at which current or voltage rises or decays.\n\nOne **time constant** is the time to reach about **63%** of the maximum value (or 36% from the minimum value).\n\nAfter two time constants, the value reaches **86%** of the maximum value (or 13% from the minimum).",
"children": [
{
"content": "A-1-1-1 (D) What is the meaning of the term \"time constant\" in an RL circuit?\nA\tThe time required for the current in the circuit to build up to 36.8% of the maximum value\nB\tThe time required for the voltage in the circuit to build up to 63.2% of the maximum value\nC\tThe time required for the voltage in the circuit to build up to 36.8% of the maximum value\nD\tThe time required for the current in the circuit to build up to 63.2% of the maximum value",
"children": [
{
"content": "> Inductance is a property of circuits that oppose changes in current. The time constant is the time current WOULD need to reach final value IF the initial rate of change COULD be maintained. The time constant in seconds equals L in henrys divided by R in ohms: the lower the resistance, the greater the rate of change resulting in greater opposition. The current after 1, 2 and 5 time constants is respectively 63%, 87% and 100% of the final value. With capacitors, the ratios are the same but they relate to voltage; the time constant then becomes R times C."
}
]
},
{
"content": "A-1-1-2 (D) What is the term for the time required for the capacitor in an RC circuit to be charged to 63.2% of the supply voltage?\nA\tAn exponential rate of one\nB\tA time factor of one\nC\tOne exponential period\nD\tOne time constant",
"children": [
{
"content": "> Capacitance is a property of circuits that oppose changes in voltage. Under charging conditions, the time constant is the time voltage WOULD need to reach the final value IF the initial rate of change COULD be maintained. The time constant in seconds equals R in ohms times C in farads: the higher the resistance, the longer the time. The voltage after 1, 2 and 5 times constants is respectively 63%, 87% and 100% of the final value. With inductors, the ratios are the same but they relate to current; the time constant then becomes L divided by R."
}
]
},
{
"content": "A-1-1-3 (A) What is the term for the time required for the current in an RL circuit to build up to 63.2% of the maximum value?\nA\tOne time constant\nB\tAn exponential period of one\nC\tA time factor of one\nD\tOne exponential rate",
"children": [
{
"content": "> Inductance is a property of circuits that oppose changes in current. The time constant is the time current WOULD need to reach final value IF the initial rate of change COULD be maintained. The time constant in seconds equals L in henrys divided by R in ohms: the lower the resistance, the greater the rate of change resulting in greater opposition. The current after 1, 2 and 5 time constants is respectively 63%, 87% and 100% of the final value. With capacitors, the ratios are the same but they relate to voltage; the time constant then becomes R times C."
}
]
},
{
"content": "A-1-1-4 (A) What is the term for the time it takes for a charged capacitor in an RC circuit to discharge to 36.8% of its initial value of stored charge?\nA\tOne time constant\nB\tA discharge factor of one\nC\tAn exponential discharge of one\nD\tOne discharge period",
"children": [
{
"content": "> Key word: DISCHARGE. The time constant is the time voltage WOULD need to reach the final value IF the initial rate of change COULD be maintained. The time constant in seconds equals R in ohms times C in farads: the higher the resistance, the longer the time. The voltage after 1, 2 and 5 times constants is respectively 63%, 87% and 100% of the final value. Heading towards ZERO, we are left with 37% (100 minus 63) and 13% (100 minus 87) respectively after 1 and 2 time constants."
}
]
},
{
"content": "A-1-1-6 (A) After two time constants, the capacitor in an RC circuit is charged to what percentage of the supply voltage?\nA\t86.5%\nB\t63.2%\nC\t95%\nD\t36.8%",
"children": [
{
"content": "> Capacitance is a property of circuits that oppose changes in voltage. Under charging conditions, the time constant is the time voltage WOULD need to reach the final value IF the initial rate of change COULD be maintained. The time constant in seconds equals R in ohms times C in farads: the higher the resistance, the longer the time. The voltage after 1, 2 and 5 times constants is respectively 63%, 87% and 100% of the final value. With inductors, the ratios are the same but they relate to current; the time constant then becomes L divided by R."
}
]
},
{
"content": "A-1-1-7 (A) After two time constants, the capacitor in an RC circuit is discharged to what percentage of the starting voltage?\nA\t13.5%\nB\t36.8%\nC\t86.5%\nD\t63.2%",
"children": [
{
"content": "> Key word: DISCHARGE. The time constant is the time voltage WOULD need to reach the final value IF the initial rate of change COULD be maintained. The time constant in seconds equals R in ohms times C in farads: the higher the resistance, the longer the time. The voltage after 1, 2 and 5 times constants is respectively 63%, 87% and 100% of the final value. Heading towards ZERO, we are left with 37% (100 minus 63) and 13% (100 minus 87) respectively after 1 and 2 time constants."
}
]
}
]
},
{
"content": "The formula is \n`tau = R L` or `tau = R C`",
"children": [
{
"content": "A-1-1-8 (C) What is the time constant of a circuit having a 100 microfarad capacitor in series with a 470 kilohm resistor?\nA\t470 seconds\nB\t0.47 seconds\nC\t47 seconds\nD\t4700 seconds",
"children": [
{
"content": "> The time constant in seconds equals R in ohms times C in farads: the higher the resistance, the longer the time. In multiplying microfarads and megohms, the prefixes cancel one another. 100 microfarads times 0.470 megohm = 100 times 0.47 = 47 seconds."
}
]
},
{
"content": "A-1-1-9 (C) What is the time constant of a circuit having a 470 microfarad capacitor in series with a 470 kilohm resistor?\nA\t47 000 seconds\nB\t470 seconds\nC\t221 seconds\nD\t221 000 seconds",
"children": [
{
"content": "> The time constant in seconds equals R in ohms times C in farads: the higher the resistance, the longer the time. In multiplying microfarads and megohms, the prefixes cancel one another. 470 microfarads times 0.470 megohm = 470 times 0.47 = 221 seconds."
}
]
},
{
"content": "A-1-1-10 (C) What is the time constant of a circuit having a 220 microfarad capacitor in series with a 470 kilohm resistor?\nA\t470 seconds\nB\t220 seconds\nC\t103 seconds\nD\t470 000 seconds",
"children": [
{
"content": "> The time constant in seconds equals R in ohms times C in farads: the higher the resistance, the longer the time. In multiplying microfarads and megohms, the prefixes cancel one another. 220 microfarads times 0.470 megohm = 220 times 0.47 = 103 seconds."
}
]
}
]
},
{
"content": "The **skin effect** causes RF current to flow in a layer at the surface of a conductor, which becomes thinner at higher frequencies and results in greater resistance.",
"children": [
{
"content": "The **skin effect** causes most RF current to flow in a thin layer along the surface of a conductor.",
"children": [
{
"content": "A-1-2-2 (C) What effect causes most of an RF current to flow along the surface of a conductor?\nA\tResonance effect\nB\tLayer effect\nC\tSkin effect\nD\tPiezoelectric effect",
"children": [
{
"content": "> Skin Effect is the tendency of AC to flow in an increasingly thinner layer at the surface of a conductor as frequency increases."
}
]
},
{
"content": "A-1-2-3 (D) Where does almost all RF current flow in a conductor?\nA\tIn a magnetic field in the centre of the conductor\nB\tIn a magnetic field around the conductor\nC\tIn the centre of the conductor\nD\tAlong the surface of the conductor",
"children": [
{
"content": "> Skin Effect is the tendency of AC to flow in an increasingly thinner layer at the surface of a conductor as frequency increases."
}
]
},
{
"content": "A-1-2-4 (B) Why does most of an RF current flow within a very thin layer under the conductor's surface?\nA\tBecause of heating of the conductor's interior\nB\tBecause of skin effect\nC\tBecause the RF resistance of a conductor is much less than the DC resistance\nD\tBecause a conductor has AC resistance due to self-inductance",
"children": [
{
"content": "> Skin Effect is the tendency of AC to flow in an increasingly thinner layer at the surface of a conductor as frequency increases."
}
]
}
]
},
{
"content": "As **frequency increases**, skin effect increases and the conduction layer is **thinner**.",
"children": [
{
"content": "A-1-2-1 (C) What is the result of skin effect?\nA\tThermal effects on the surface of the conductor increase impedance\nB\tThermal effects on the surface of the conductor decrease impedance\nC\tAs frequency increases, RF current flows in a thinner layer of the conductor, closer to the surface\nD\tAs frequency decreases, RF current flows in a thinner layer of the conductor, closer to the surface",
"children": [
{
"content": "> Skin Effect is the tendency of AC to flow in an increasingly thinner layer at the surface of a conductor as frequency increases."
}
]
}
]
},
{
"content": "The practical consequence of this is that for the same size wire at higher and **higher frequencies**, less and less of the cross-section conducts current. So, it starts to look like a thinner wire, with a consequently **higher resistance**. (Therefore, you start to need larger or different types of conductors for long runs at UHF and microwave frequencies, for example.)",
"children": [
{
"content": "A-1-2-5 (D) Why is the resistance of a conductor different for RF currents than for direct currents?\nA\tBecause of the Hertzberg effect\nB\tBecause conductors are non-linear devices\nC\tBecause the insulation conducts current at high frequencies\nD\tBecause of skin effect",
"children": [
{
"content": "> Skin Effect is the tendency of AC to flow in an increasingly thinner layer at the surface of a conductor as frequency increases."
}
]
}
]
}
]
},
{
"content": "**Capacitors** and **inductors** establish electrostatic and electromagnetic fields respectively, both of which store potential energy.",
"children": [
{
"content": "Capacitors set up an **electrostatic field** between their charged plates.",
"children": [
{
"content": "A-1-2-10 (A) Between the charged plates of a capacitor there is:\nA\tan electrostatic field\nB\ta magnetic field\nC\ta cloud of electrons\nD\tan electric current",
"children": [
{
"content": "> Voltage across a capacitor creates an electrostatic field between the plates. An electrostatic field is the electric field present between objects with different static electrical charges. An electric field is a space where an electrical charge exerts a force (attraction or repulsion) on other charges."
}
]
}
]
},
{
"content": "The readiness of a capacitor to store an electric charge is called capacitance, measured in Farads.",
"children": [
{
"content": "A-1-2-6 (D) What unit measures the ability of a capacitor to store electrical charge?\nA\tCoulomb\nB\tWatt\nC\tVolt\nD\tFarad",
"children": [
{
"content": "> Capacitors store energy in an electrostatic field. The capacitance in farads is one factor influencing how much energy can be stored in a capacitor. The coulomb is a quantity of electrons ( 6 times 10 exponent 18 ). One farad accepts a charge of one coulomb when subjected to one volt. The watt is a rate of doing work (one joule per second). One volt, a force, moves one coulomb with one joule of energy."
}
]
}
]
},
{
"content": "Wires carrying current (such as inductors) are surrounded by an **electromagnetic field**.",
"children": [
{
"content": "A-1-2-7 (A) A wire has a current passing through it. Surrounding this wire there is:\nA\tan electromagnetic field\nB\tan electrostatic field\nC\ta cloud of electrons\nD\ta skin effect that diminishes with distance",
"children": [
{
"content": "> An electromagnetic field is the magnetic field created around a conductor carrying current. A magnetic field is a space around a magnet or a conductor where a magnetic force is present. A magnetic field is composed of magnetic lines of force. An electrostatic field is the electric field present between objects with different static electrical charges. An electric field is a space where an electrical charge exerts a force (attraction or repulsion) on other charges."
}
]
}
]
},
{
"content": "The unit of inductance is the **Henry**.",
"children": [
{
"content": "A-1-2-11 (B) Energy is stored within an inductor that is carrying a current. The amount of energy depends on this current, but it also depends on a property of the inductor. This property has the following unit:\nA\twatt\nB\thenry\nC\tcoulomb\nD\tfarad",
"children": [
{
"content": "> Inductors store energy in an electromagnetic field. The inductance in henrys is one factor influencing how much energy can be stored in an inductor. One henry produces one volt of counter EMF with current changing at a rate of one ampere per second. The coulomb is a quantity of electrons ( 6 times 10 exponent 18 ). One farad accepts a charge of one coulomb when subjected to one volt. The watt is a rate of doing work (one joule per second)."
}
]
}
]
},
{
"content": "The **left hand rule** describes the orientation of the magnetic field relative to **electron** flow.",
"children": [
{
"content": "A-1-2-8 (C) In what direction is the magnetic field oriented about a conductor in relation to the direction of electron flow?\nA\tIn the same direction as the current\nB\tIn the direct opposite to the current\nC\tIn the direction determined by the left-hand rule\nD\tIn all directions",
"children": [
{
"content": "> The 'Left-hand Rule': position the left hand with your thumb pointing in the direction of electron flow; encircle the conductor with the remaining fingers, the fingers point in the direction of the magnetic lines of force. [ Using conventional current flow, this would become the Right-hand rule. ]"
}
]
}
]
},
{
"content": "Both these electromagnetic and electrostatic fields store potential energy.",
"children": [
{
"content": "A-1-2-9 (A) What is the term for energy that is stored in an electromagnetic or electrostatic field?\nA\tPotential energy\nB\tKinetic energy\nC\tAmpere-joules\nD\tJoule-coulombs",
"children": [
{
"content": "> Key word: STORED. Potential: \"capable of coming into being or action (Canadian Oxford)\". Kinetic: \"of or due to motion (Canadian Oxford)\"."
}
]
}
]
},
{
"content": "In an inductor, a **Back-EMF** is a voltage that opposes an applied voltage.",
"children": [
{
"content": "A-1-1-5 (A) What is meant by \"back EMF\"?\nA\tA voltage that opposes the applied EMF\nB\tA current that opposes the applied EMF\nC\tAn opposing EMF equal to R times C percent of the applied EMF\nD\tA current equal to the applied EMF",
"children": [
{
"content": "> 'Back EMF' or 'counter electromotive force' is the voltage induced by changing current in an inductor. It is the force opposing changes in current through inductors."
}
]
}
]
}
]
},
{
"content": "The **resonant frequency** of an RLC circuit depends *only* on the value of L and C.\n\n```\n 1\nf_r,series = ----------------\n 2 pi sqrt( L C )\n\n```",
"children": [
{
"content": "[Series-resonant circuits](https://www.electronics-tutorials.ws/accircuits/series-resonance.html) admit **much** current at the resonant frequency (impedance is minimum).",
"children": [
{
"content": "At resonance, the reactances are equal and opposite, resulting in **zero** net reactance. The two components appear as a short. Net current flow is at a maximum, determined by the value of R."
}
]
},
{
"content": "[Parallel LC circuits](https://www.electronics-tutorials.ws/accircuits/parallel-resonance.html) admit **little** current at the resonant frequency (impedance is maximum).",
"children": [
{
"content": "Again, at resonance, the reactances are equal and opposite.\n\nTherefore, current in the capacitor and inductor is equal and opposite (totally out of phase)."
},
{
"content": "The net current flow through them is **zero**, and the two components together appear as an **open**.\n\nThe **only** current that flows is through the resistor, and again, the current flow at resonance is determined solely by R.\n \nThis time, however, the net current is at minimum. Off-resonance, the inductor and capacitor admit more current."
},
{
"content": "**Off** resonance, current flows through all three components, net current is greater, impedance is lesser, and admittance is greater."
}
]
},
{
"content": "The resonant frequency of a **series** L C circuit is given by:\n\n```\n 1\nf_r,series = ----------------\n 2 pi sqrt( L C )\n\n```\n",
"children": [
{
"content": "A-1-3-2 (D) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 40 microhenrys and C is 200 picofarads?\nA\t1.99 kHz\nB\t1.99 MHz\nC\t1.78 kHz\nD\t1.78 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 40 times 200 equals 8000 ; The square root of 8000 is 89.4 ; 89.4 times 2 times 3.14 is 561.4 ; 1000 divided by 561.4 is 1.78 MHz."
}
]
},
{
"content": "A-1-3-3 (C) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 50 microhenrys and C is 10 picofarads?\nA\t3.18 MHz\nB\t3.18 kHz\nC\t7.12 MHz\nD\t7.12 kHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 50 times 10 equals 500 ; The square root of 500 is 22.4 ; 22.4 times 2 times 3.14 is 140.7 ; 1000 divided by 140.7 is 7.11 MHz."
}
]
},
{
"content": "A-1-3-4 (D) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 25 microhenrys and C is 10 picofarads?\nA\t63.7 MHz\nB\t10.1 kHz\nC\t63.7 kHz\nD\t10.1 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 25 times 10 equals 250 ; The square root of 250 is 15.8 ; 15.8 times 2 times 3.14 is 99.2 ; 1000 divided by 99.2 is 10.08 MHz."
}
]
},
{
"content": "A-1-3-5 (D) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 3 microhenrys and C is 40 picofarads?\nA\t13.1 MHz\nB\t13.1 kHz\nC\t14.5 kHz\nD\t14.5 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 3 times 40 equals 120 ; The square root of 120 is 11 ; 11 times 2 times 3.14 is 69.1 ; 1000 divided by 69.1 is 14.47 MHz."
}
]
},
{
"content": "A-1-3-6 (D) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 4 microhenrys and C is 20 picofarads?\nA\t19.9 MHz\nB\t19.9 kHz\nC\t17.8 kHz\nD\t17.8 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 4 times 20 equals 80 ; The square root of 80 is 8.9 ; 8.9 times 2 times 3.14 is 55.9 ; 1000 divided by 55.9 is 17.89 MHz."
}
]
},
{
"content": "A-1-3-7 (B) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 8 microhenrys and C is 7 picofarads?\nA\t2.13 MHz\nB\t21.3 MHz\nC\t28.4 MHz\nD\t2.84 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 8 times 7 equals 56 ; The square root of 56 is 7.5 ; 7.5 times 2 times 3.14 is 47.1 ; 1000 divided by 47.1 is 21.23 MHz."
}
]
},
{
"content": "A-1-3-8 (B) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 3 microhenrys and C is 15 picofarads?\nA\t23.7 kHz\nB\t23.7 MHz\nC\t35.4 MHz\nD\t35.4 kHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 3 times 15 equals 45 ; The square root of 45 is 6.7 ; 6.7 times 2 times 3.14 is 42.1 ; 1000 divided by 42.1 is 23.75 MHz."
}
]
},
{
"content": "A-1-3-9 (A) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 4 microhenrys and C is 8 picofarads?\nA\t28.1 MHz\nB\t49.7 MHz\nC\t49.7 kHz\nD\t28.1 kHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 4 times 8 equals 32 ; The square root of 32 is 5.7 ; 5.7 times 2 times 3.14 is 35.8 ; 1000 divided by 35.8 is 27.93 MHz."
}
]
},
{
"content": "A-1-3-10 (A) What is the resonant frequency of a series RLC circuit, if R is 47 ohms, L is 1 microhenry and C is 9 picofarads?\nA\t53.1 MHz\nB\t5.31 MHz\nC\t17.7 MHz\nD\t1.77 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 1 times 9 equals 9 ; The square root of 9 is 3 ; 3 times 2 times 3.14 is 18.8 ; 1000 divided by 18.8 is 53.19 MHz."
}
]
},
{
"content": "A-1-4-1 (A) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 1 microhenry and C is 10 picofarads?\nA\t50.3 MHz\nB\t15.9 kHz\nC\t50.3 kHz\nD\t15.9 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 1 times 10 equals 10 ; The square root of 9 is 3.2 ; 3.2 times 2 times 3.14 is 20.1 ; 1000 divided by 20.1 is 49.75 MHz."
}
]
},
{
"content": "A-1-4-2 (D) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 2 microhenrys and C is 15 picofarads?\nA\t29.1 kHz\nB\t5.31 MHz\nC\t5.31 kHz\nD\t29.1 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 2 times 15 equals 30 ; The square root of 30 is 5.5 ; 5.5 times 2 times 3.14 is 34.5 ; 1000 divided by 34.5 is 28.99 MHz."
}
]
},
{
"content": "A-1-3-1 (D) What is the resonant frequency of a series RLC circuit if R is 47 ohms, L is 50 microhenrys and C is 40 picofarads?\nA\t1.78 MHz\nB\t7.96 MHz\nC\t79.6 MHz\nD\t3.56 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 50 times 40 equals 2000 ; The square root of 2000 is 44.7 ; 44.7 times 2 times 3.14 is 280.7 ; 1000 divided by 280.7 is 3.56 MHz."
}
]
}
]
},
{
"content": "The resonant frequency of a **parallel** L C circuit is given by:\n\n```\n 1\nf_r,parallel = ----------------\n 2 pi sqrt( L C )\n\n```",
"children": [
{
"content": "A-1-4-3 (B) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 5 microhenrys and C is 9 picofarads?\nA\t3.54 kHz\nB\t23.7 MHz\nC\t23.7 kHz\nD\t3.54 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 5 times 9 equals 45 ; The square root of 45 is 6.7 ; 6.7 times 2 times 3.14 is 42.1 ; 1000 divided by 42.1 is 23.75 MHz."
}
]
},
{
"content": "A-1-4-4 (A) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 2 microhenrys and C is 30 picofarads?\nA\t20.5 MHz\nB\t2.65 MHz\nC\t2.65 kHz\nD\t20.5 kHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 2 times 30 equals 60 ; The square root of 60 is 7.7 ; 7.7 times 2 times 3.14 is 48.4 ; 1000 divided by 48.4 is 20.66 MHz."
}
]
},
{
"content": "A-1-4-8 (D) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 10 microhenrys and C is 50 picofarads?\nA\t7.12 kHz\nB\t3.18 MHz\nC\t3.18 kHz\nD\t7.12 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 10 times 50 equals 500 ; The square root of 500 is 22.4 ; 22.4 times 2 times 3.14 is 140.7 ; 1000 divided by 140.7 is 7.11 MHz."
}
]
},
{
"content": "A-1-4-5 (B) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 15 microhenrys and C is 5 picofarads?\nA\t18.4 kHz\nB\t18.4 MHz\nC\t2.12 kHz\nD\t2.12 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 15 times 5 equals 75 ; The square root of 75 is 8.7 ; 8.7 times 2 times 3.14 is 54.6 ; 1000 divided by 54.6 is 18.32 MHz."
}
]
},
{
"content": "A-1-4-9 (B) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 200 microhenrys and C is 10 picofarads?\nA\t7.96 kHz\nB\t3.56 MHz\nC\t3.56 kHz\nD\t7.96 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 200 times 10 equals 2000 ; The square root of 2000 is 44.7 ; 44.7 times 2 times 3.14 is 280.7 ; 1000 divided by 280.7 is 3.56 MHz."
}
]
},
{
"content": "A-1-4-10 (A) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 90 microhenrys and C is 100 picofarads?\nA\t1.68 MHz\nB\t1.77 kHz\nC\t1.77 MHz\nD\t1.68 kHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 90 times 100 equals 9000 ; The square root of 9000 is 94.9 ; 94.9 times 2 times 3.14 is 596 ; 1000 divided by 596 is 1.68 MHz."
}
]
},
{
"content": "A-1-4-6 (D) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 3 microhenrys and C is 40 picofarads?\nA\t1.33 kHz\nB\t1.33 MHz\nC\t14.5 kHz\nD\t14.5 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 3 times 40 equals 120 ; The square root of 120 is 11 ; 11 times 2 times 3.14 is 69.1 ; 1000 divided by 69.1 is 14.47 MHz."
}
]
},
{
"content": "A-1-4-7 (D) What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 40 microhenrys and C is 6 picofarads?\nA\t6.63 MHz\nB\t6.63 kHz\nC\t10.3 kHz\nD\t10.3 MHz",
"children": [
{
"content": "> Resonant frequency equals 1 over ( 2 pi times the square root of L times C ). Restating for frequency in megahertz becomes 1000 over ( 2 pi times the square root of microhenrys times picofarads ). 40 times 6 equals 240 ; The square root of 240 is 15.5 ; 15.5 times 2 times 3.14 is 97.3 ; 1000 divided by 97.3 is 10.28 MHz."
}
]
}
]
},
{
"content": "Note that in both cases, the formulas are the same, and resistance does not affect the resonant frequency."
},
{
"content": "Going backward is just a little tricky because of the square root.",
"children": [
{
"content": "A-1-3-11 (C) What is the value of capacitance (C) in a **series** R-L-C circuit, if the circuit resonant frequency is 14.25 MHz and L is 2.84 microhenrys?\nA\t44 microfarads\nB\t2.2 picofarads\nC\t44 picofarads\nD\t2.2 microfarads",
"children": [
{
"content": "> Method A: Reactances are equal at resonance. XL = 2 times 3.14 times 14.25 times 2.84 = 254.2 ohms. XC = 1 over ( 2 pi f C ). Restating for f in megahertz and C in picofarads, XC = one million over 2 pi megahertz times picofarads. Thus, C = one million over ( 2 pi f XC ) ; 2 times 3.14 times 14.25 times 254.2 = 22 748 ; one million divided by 22 748 = 43.96 picofarads. Method B: at 14 MHz, C has to be in picofarads; test the two answers in picofarads with \"resonant frequency in megahertz equals 1000 over ( 2 pi times the square root of microhenrys times picofarads )\"."
}
]
},
{
"content": "A-1-4-11 (B) What is the value of inductance (L) in a **parallel** RLC circuit, if the resonant frequency is 14.25 MHz and C is 44 picofarads?\nA\t0.353 microhenry\nB\t2.8 microhenrys\nC\t253.8 millihenrys\nD\t3.9 millihenrys",
"children": [
{
"content": "> Method A: Reactances are equal at resonance. XC = 1 over ( 2 pi f C ). Restating for f in megahertz and C in picofarads, XC = one million over (2 pi times megahertz times picofarads). XC = one million divided by ( 2 times 3.14 times 14.25 times 44 ) = 254 ohms. With XL = 2 pi f L, L is XL divided by 2 pi f: 254 divided by ( 2 times 3.14 times 14.25 ) = 2.8 microhenrys. Method B: at 14 MHz, L has to be in microhenrys; test the two answers in microhenrys with \"resonant frequency in megahertz equals 1000 over ( 2 pi times the square root of microhenrys times picofarads )\"."
}
]
}
]
}
]
},
{
"content": "The **Q-factor** of an RLC circuit depends on the resistance of *R* relative to the reactance *X* of *L* and *C*.\n\n```\n R \nQ_p = - ; X_C = 1/(2 pi f C) \n X X_L = 2 pi f L \n```",
"children": [
{
"content": "![](https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/accircuits-acp211.gif)"
},
{
"content": "Crystal filters have high Q-factor.",
"children": [
{
"content": "A-2-11-5 (C) A quartz crystal filter is superior to an LC filter for narrow bandpass applications because of the:\nA\tLC circuit's high Q\nB\tcrystal's simplicity\nC\tcrystal's high Q\nD\tcrystal's low Q",
"children": [
{
"content": "> Piezoelectric crystals behave like tuned circuits with an extremely high \"Q\" (\"Quality Factor\", in excess of 25 000). Their accuracy and stability are outstanding."
}
]
}
]
},
{
"content": "In a parallel tuned circuit, the so called damping resistor increases the filter bandwidth at the expense of Q",
"children": [
{
"content": "A-1-5-11 (B) Why is a resistor often included in a parallel resonant circuit?\nA\tTo increase the Q and decrease bandwidth\nB\tTo decrease the Q and increase the bandwidth\nC\tTo increase the Q and decrease the skin effect\nD\tTo decrease the Q and increase the resonant frequency",
"children": [
{
"content": "> A Damping Resistor can be placed across a parallel resonant circuit, or in series with a series resonant circuit, to lower the Q. Reducing the Quality factor increases bandwidth.\n\n' -- -- -- --"
}
]
}
]
},
{
"content": "The formula for Q-factor is different for [series](https://www.electronics-tutorials.ws/accircuits/series-resonance.html) and [parallel](https://www.electronics-tutorials.ws/accircuits/parallel-resonance.html) circuits, but the exam only asks about **parallel** circuits.\n\n```\n R \nQ_p = - ; X_C = 1/(2 pi f C) \n X X_L = 2 pi f L \n```\n",
"children": [
{
"content": "A-1-5-1 (A) What is the Q of a **parallel** RLC circuit, if it is resonant at 14.128 MHz, L is 2.7 microhenrys and R is 18 kilohms?\nA\t75.1\nB\t7.51\nC\t0.013\nD\t71.5",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 14.128 times 2.7 = 240 ( the mega in megahertz cancels the micro in microhenrys). Q = 18 000 divided by 240 = 75 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-10 (D) What is the Q of a **parallel** RLC circuit, if it is resonant at 3.625 MHz, L is 43 microhenrys and R is 1.8 kilohms?\nA\t0.543\nB\t54.3\nC\t23\nD\t1.84",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 3.625 times 43 = 979 ( the mega in megahertz cancels the micro in microhenrys). Q = 1800 divided by 979 = 1.84 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-9 (B) What is the Q of a **parallel** RLC circuit, if it is resonant at 3.625 MHz, L is 42 microhenrys and R is 220 ohms?\nA\t0.00435\nB\t0.23\nC\t2.3\nD\t4.35",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 3.625 times 42 = 956 ( the mega in megahertz cancels the micro in microhenrys). Q = 220 divided by 956 = 0.23 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-8 (D) What is the Q of a **parallel** RLC circuit, if it is resonant at 3.625 MHz, L is 3 microhenrys and R is 2.2 kilohms?\nA\t25.6\nB\t31.1\nC\t0.031\nD\t32.2",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 3.625 times 3 = 68 ( the mega in megahertz cancels the micro in microhenrys). Q = 2200 divided by 68 = 32.3 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-7 (D) What is the Q of a **parallel** RLC circuit, if it is resonant at 7.125 MHz, L is 12.6 microhenrys and R is 22 kilohms?\nA\t22.1\nB\t0.0256\nC\t25.6\nD\t39",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 7.125 times 12.6 = 564 ( the mega in megahertz cancels the micro in microhenrys). Q = 22 000 divided by 564 = 39 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-6 (C) What is the Q of a **parallel** RLC circuit, if it is resonant at 7.125 MHz, L is 10.1 microhenrys and R is 100 ohms?\nA\t0.00452\nB\t4.52\nC\t0.221\nD\t22.1",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 7.125 times 10.1 = 452 ( the mega in megahertz cancels the micro in microhenrys). Q = 100 divided by 452 = 0.22 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-5 (A) What is the Q of a **parallel** RLC circuit, if it is resonant at 7.125 MHz, L is 8.2 microhenrys and R is 1 kilohm?\nA\t2.73\nB\t36.8\nC\t0.368\nD\t0.273",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 7.125 times 8.2 = 367 ( the mega in megahertz cancels the micro in microhenrys). Q = 1000 divided by 367 = 2.7 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-3 (A) What is the Q of a **parallel** RLC circuit, if it is resonant at 4.468 MHz, L is 47 microhenrys and R is 180 ohms?\nA\t0.136\nB\t7.35\nC\t0.00735\nD\t13.3",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 4.468 times 47 = 1319 ( the mega in megahertz cancels the micro in microhenrys). Q = 180 divided by 1319 = 0.136 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-2 (A) What is the Q of a **parallel** RLC circuit, if it is resonant at 14.128 MHz, L is 4.7 microhenrys and R is 18 kilohms?\nA\t43.1\nB\t13.3\nC\t0.023\nD\t4.31",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 14.128 times 4.7 = 417 ( the mega in megahertz cancels the micro in microhenrys). Q = 18 000 divided by 417 = 43 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
},
{
"content": "A-1-5-4 (B) What is the Q of a **parallel** RLC circuit, if it is resonant at 14.225 MHz, L is 3.5 microhenrys and R is 10 kilohms?\nA\t71.5\nB\t31.9\nC\t7.35\nD\t0.0319",
"children": [
{
"content": "> Reactance = 2 pi f L = 2 times 3.14 times 14.225 times 3.5 = 313 ( the mega in megahertz cancels the micro in microhenrys). Q = 10 000 divided by 313 = 31.9 . In a PARALLEL circuit loaded by a resistor, Q = Resistance divided by Reactance: the higher the parallel resistance, the lesser the effect on the response curve. Parallel resistance lowers the Q of a parallel tuned circuit. A parallel Damping Resistor is used to increase bandwidth."
}
]
}
]
}
]
},
{
"content": "**Filters** are resonant circuits characterized by their frequency response.",
"children": [
{
"content": "The three general groupings of filters are **high-pass**, **low-pass**, and **band-pass**.",
"children": [
{
"content": "A-2-12-1 (D) What are the three general groupings of filters?\nA\tHartley, Colpitts and Pierce\nB\tAudio, radio and capacitive\nC\tInductive, capacitive and resistive\nD\tHigh-pass, low-pass and band-pass",
"children": [
{
"content": "> There are 4 categories of filters: high-pass, low-pass, band-pass and band-stop. Hartley, Colpitts and Pierce are oscillator configurations. \"Capacitive\" is not a range of frequencies like audio or radio. Resistors do not discriminate frequency."
}
]
}
]
},
{
"content": "**Resonant cavities** have a *narrow* bandpass and are used at VHF and above. Their length is roughly a *quarter wavelength* long. Consequently, their size becomes unwieldy below roughly 50 MHz.",
"children": [
{
"content": "A-2-12-5 (B) Resonant cavities are used by amateurs as a:\nA\thigh-pass filter above 30 MHz\nB\tnarrow bandpass filter at VHF and higher frequencies\nC\tpower line filter\nD\tlow-pass filter below 30 MHz",
"children": [
{
"content": "> The quarter wavelength Resonant Cavity behaves like a very high \"Q\" filter. Due to their physical size, they become practical only at VHF frequencies: at 50 MHz (6 m), the length of the cavity is 1.5 m (one quarter wavelength)."
}
]
},
{
"content": "A-2-12-6 (D) On VHF and above, 1/4 wavelength coaxial cavities are used to give protection from high-level signals. For a frequency of approximately 50 MHz, the diameter of such a device would be about 10 cm (4 in). What would be its approximate length?\nA\t0.6 metres (2 ft)\nB\t2.4 metres (8 ft)\nC\t3.7 metres (12 ft)\nD\t1.5 metres (5 ft)",
"children": [
{
"content": "> The quarter wavelength Resonant Cavity behaves like a very high \"Q\" filter (around 3000). Due to their physical size, they become practical only at VHF frequencies: at 50 MHz (6 m), the length of the cavity is 1.5 m (one quarter wavelength)."
}
]
},
{
"content": "A-2-12-11 (D) Which of the following filter types is not suitable for use at audio and low radio frequencies?\nA\tElliptical\nB\tChebyshev\nC\tButterworth\nD\tCavity",
"children": [
{
"content": "> The quarter wavelength Resonant Cavity behaves like a very high \"Q\" filter. Due to their physical size, they become practical only at VHF frequencies: at 50 MHz (6 m), the length of the cavity is 1.5 m (one quarter wavelength)."
}
]
}
]
},
{
"content": "**Butterworth** filters have a *flat* response. (Mnemonic: *\"Smooth as butter.\"*)",
"children": [
{
"content": "A-2-12-2 (C) What are the distinguishing features of a Butterworth filter?\nA\tIt only requires conductors\nB\tIt only requires capacitors\nC\tIt has a maximally flat response over its pass-band\nD\tThe product of its series and shunt-element impedances is a constant for all frequencies",
"children": [
{
"content": "> The Butterworth class of filters exhibit \"maximally flat response\": smooth response, no passband ripple. Their frequency response is as flat as mathematically possible in the passband, no bumps or variations (ripple) [first described by British engineer Stephen Butterworth]. The Chebyshev class of filters [in honour of Pafnuty Chebyshev, a Russian mathematician] have steeper cutoff slopes and more ripple than Butterworth filters. Elliptic filters are sharper than the previous two. Here is a mnemonic trick: \"The Butterworth's response is smooth as butter\"."
}
]
},
{
"content": "A-2-12-9 (B) What is the primary advantage of the Butterworth filter over the Chebyshev filter?\nA\tIt requires only capacitors\nB\tIt has maximally flat response over its passband\nC\tIt allows ripple in the passband in return for steeper skirts\nD\tIt requires only inductors",
"children": [
{
"content": "> The Butterworth class of filters exhibit \"maximally flat response\": smooth response, no passband ripple. Their frequency response is as flat as mathematically possible in the passband, no bumps or variations (ripple) [first described by British engineer Stephen Butterworth]. The Chebyshev class of filters [in honour of Pafnuty Chebyshev, a Russian mathematician] have steeper cutoff slopes and more ripple than Butterworth filters. Elliptic filters are sharper than the previous two. Here is a mnemonic trick: \"The Butterworth's response is smooth as butter\"."
}
]
}
]
},
{
"content": "**Chebyshev** filters have a sharper cuttoff, but a *rippled* bandpass.",
"children": [
{
"content": "A-2-12-3 (B) Which filter type is described as having ripple in the passband and a sharp cutoff?\nA\tA Butterworth filter\nB\tA Chebyshev filter\nC\tAn active LC filter\nD\tA passive op-amp filter",
"children": [
{
"content": "> The Butterworth class of filters exhibit \"maximally flat response\": smooth response, no passband ripple. Their frequency response is as flat as mathematically possible in the passband, no bumps or variations (ripple) [first described by British engineer Stephen Butterworth]. The Chebyshev class of filters [in honour of Pafnuty Chebyshev, a Russian mathematician] have steeper cutoff slopes and more ripple than Butterworth filters. Elliptic filters are sharper than the previous two. Here is a mnemonic trick: \"The Butterworth's response is smooth as butter\"."
}
]
},
{
"content": "A-2-12-4 (B) What are the distinguishing features of a Chebyshev filter?\nA\tIt has a maximally flat response in the passband\nB\tIt allows ripple in the passband in return for steeper skirts\nC\tIt requires only inductors\nD\tIt requires only capacitors",
"children": [
{
"content": "> The Butterworth class of filters exhibit \"maximally flat response\": smooth response, no passband ripple. Their frequency response is as flat as mathematically possible in the passband, no bumps or variations (ripple) [first described by British engineer Stephen Butterworth]. The Chebyshev class of filters [in honour of Pafnuty Chebyshev, a Russian mathematician] have steeper cutoff slopes and more ripple than Butterworth filters. Elliptic filters are sharper than the previous two. Here is a mnemonic trick: \"The Butterworth's response is smooth as butter\"."
}
]
},
{
"content": "A-2-12-10 (C) What is the primary advantage of the Chebyshev filter over the Butterworth filter?\nA\tIt requires only inductors\nB\tIt has maximally flat response over the passband\nC\tIt allows ripple in the passband in return for steeper skirts\nD\tIt requires only capacitors",
"children": [
{
"content": "> The Butterworth class of filters exhibit \"maximally flat response\": smooth response, no passband ripple. Their frequency response is as flat as mathematically possible in the passband, no bumps or variations (ripple) [first described by British engineer Stephen Butterworth]. The Chebyshev class of filters [in honour of Pafnuty Chebyshev, a Russian mathematician] have steeper cutoff slopes and more ripple than Butterworth filters. Elliptic filters are sharper than the previous two. Here is a mnemonic trick: \"The Butterworth's response is smooth as butter\"."
}
]
}
]
},
{
"content": "A **helical resonator** is a filter formed from coiled feedline, approriate for VHF & UHF applications They are used to sanitize receiver inputs.",
"children": [
{
"content": "A-2-12-7 (C) A device which helps with **receiver overload** and spurious responses at VHF, UHF and above may be installed in the receiver front end. It is called a:\nA\tdirectional coupler\nB\tduplexer\nC\thelical resonator\nD\tdiplexer",
"children": [
{
"content": "> The Helical Resonator, based on the concept of a resonant helically-wound section of transmission line within a shielded enclosure, achieves selectivity comparable to the quarter-wave resonant cavity but with a substantial size reduction."
}
]
}
]
},
{
"content": "None of the filters described here have a bandpass that is 6 MHz wide.",
"children": [
{
"content": "A-2-12-8 (C) Where you require **bandwidth** at VHF and higher frequencies about equal to a **television channel**, a good choice of filter is the:\nA\tButterworth\nB\tChebyshev\nC\tnone of the other answers\nD\tresonant cavity",
"children": [
{
"content": "> The bandwidth of a fast-scan TV channel is 6 MHz; that is much too wide for any of the filters listed."
},
{
"content": "(Which makes me wonder how CATV filters work.)"
}
]
}
]
}
]
},
{
"content": "[**Crystal lattice filters**](https://www.electronics-notes.com/articles/radio/rf-filters/what-is-crystal-filter-basics.php) have high Q.",
"children": [
{
"content": "Crystal elements use the **piezoelectric** effect, in which electrical energy and **mechanical strain** are transformed.",
"children": [
{
"content": "A-2-11-10 (D) Crystal oscillators, filters and microphones depend upon which principle?\nA\tHertzberg effect\nB\tFerro-resonance\nC\tOvertone effect\nD\tPiezoelectric effect",
"children": [
{
"content": "> The piezoelectric property of quartz (generating electricity under mechanical stress, bending when subjected to electric field) is used in crystal-based oscillators, radio-frequency crystal filters, such as the lattice filter, and crystal microphones. The Active Filter is based on an active device, generally an operational amplifier, and a network of resistors and capacitors."
}
]
},
{
"content": "A-2-11-6 (D) Piezoelectricity is generated by:\nA\ttouching crystals with magnets\nB\tadding impurities to a crystal\nC\tmoving a magnet near a crystal\nD\tdeforming certain crystals",
"children": [
{
"content": "> The piezoelectric property of quartz is two-fold: apply mechanical stress to a crystal and it produces a small electrical field; subject quartz to an electrical field and the crystal changes dimensions slightly. Crystals are capable of resonance either at a fundamental frequency depending on their physical dimensions or at overtone frequencies near odd-integer multiples (3rd, 5th, 7th, etc.). Piezoelectric crystals can serve as filters because of their extremely high \"Q\" (> 25 000) or as stable, noise-free and accurate frequency references."
}
]
}
]
},
{
"content": "Crystal elements are **not** appropriate for **active** filters, but *are* used in lattice filters, oscillators, and microphones.",
"children": [
{
"content": "A-2-11-11 (C) Crystals are not applicable to which of the following?\nA\tLattice filters\nB\tOscillators\nC\tActive filters\nD\tMicrophones",
"children": [
{
"content": "> The piezoelectric property of quartz (generating electricity under mechanical stress, bending when subjected to electric field) is used in crystal-based oscillators, radio-frequency crystal filters, such as the lattice filter, and crystal microphones. The Active Filter is based on an active device, generally an operational amplifier, and a network of resistors and capacitors.\n\n' -- -- -- --"
}
]
}
]
},
{
"content": "Crystal lattice filters are made up of multiple crystals with different frequencies. The choice of frequencies determine the filter characteristics.",
"children": [
{
"content": "A-2-11-2 (C) What factor determines the bandwidth and response shape of a crystal lattice filter?\nA\tThe gain of the RF stage following the filter\nB\tThe amplitude of the signals passing through the filter\nC\tThe relative frequencies of the individual crystals\nD\tThe centre frequency chosen for the filter",
"children": [
{
"content": "> A filter with narrow bandwidth and steep skirts made with quartz crystals. \"Lattice: a structure of crossed laths with spaces between, used as a screen or fence.\" The frequency separation between the crystals sets the bandwidth and the response shape. Crystal lattice filter: uses two matched pairs of series crystals and a higher-frequency matched pair of shunt crystals in a balanced configuration. Half-lattice crystal filter: uses two crystals in an unbalanced configuration. Such filters can be cascaded. A 'Crystal Gate' uses a single crystal."
}
]
}
]
},
{
"content": "The frequency response of a crystal lattice filter has a **narrow bandwidth** and **steep skirts**, that is, they have very **high Q**.",
"children": [
{
"content": "A-2-11-1 (A) What is a crystal lattice filter?\nA\tA filter with narrow bandwidth and steep skirts made using quartz crystals\nB\tA filter with wide bandwidth and shallow skirts made using quartz crystals\nC\tAn audio filter made with four quartz crystals that resonate at 1 kHz intervals\nD\tA power supply filter made with interlaced quartz crystals",
"children": [
{
"content": "> A filter with narrow bandwidth and steep skirts made with quartz crystals. \"Lattice: a structure of crossed laths with spaces between, used as a screen or fence.\" The frequency separation between the crystals sets the bandwidth and the response shape. Crystal lattice filter: uses two matched pairs of series crystals and a higher-frequency matched pair of shunt crystals in a balanced configuration. Half-lattice crystal filter: uses two crystals in an unbalanced configuration. Such filters can be cascaded. A 'Crystal Gate' uses a single crystal."
}
]
},
{
"content": "A-2-11-7 (B) Electrically, what does a crystal look like?\nA\tA variable tuned circuit\nB\tA very high Q tuned circuit\nC\tA very low Q tuned circuit\nD\tA variable capacitance",
"children": [
{
"content": "> Piezoelectric crystals behave like tuned circuits with an extremely high \"Q\" (\"Quality Factor\", in excess of 25 000). Their accuracy and stability are outstanding."
}
]
}
]
},
{
"content": "For example, the filter bandwidth of an SSB filter should be about 3 kHz.",
"children": [
{
"content": "A-2-11-3 (A) For single-sideband phone emissions, what would be the bandwidth of a good crystal lattice filter?\nA\t2.4 kHz\nB\t15 kHz\nC\t500 Hz\nD\t6 kHz",
"children": [
{
"content": "> Speech frequencies on a communication-grade SSB voice channel range from 300 hertz to 3000 hertz and thus require a bandwidth of 2.7 kHz; 2.1 kHz is a good compromise between fidelity and selectivity. 15 kHz is the bandwidth of FM, 6 kHz is for AM, 500 Hz is a common filter width for CW."
}
]
}
]
}
]
}
]
},
{
"content": "{L03} Semiconductors.",
"children": [
{
"content": "**Semiconductors in general**\nThe exam deals with:\n* Common semiconductor elements (Si, Ge, GaAs).\n* Basics of doped silicon (P-type, N-type).",
"children": [
{
"content": "Semiconductors act as conductors, insulators, or in-between.",
"children": [
{
"content": "A-2-1-8 (B) An element which is sometimes an insulator and sometimes a conductor is called a:\nA\tP-type conductor\nB\tsemiconductor\nC\tintrinsic conductor\nD\tN-type conductor",
"children": [
{
"content": "> The most basic semiconductor materials are silicon and germanium. Atoms in metallic elements hold their peripheral electrons loosely, such materials make good conductors. Peripheral electrons in non-metallic elements are tightly bound, such materials are insulators. Germanium and silicon fall somewhere between the two categories but are mostly insulators when pure. Doping with impurities increases their conductivity."
}
]
}
]
},
{
"content": "Some common semiconducting elements are:\n* **Silicon**,\n* **germanium**, and\n* **gallium arsenide** (for microwave applications).",
"children": [
{
"content": "A-2-1-9 (B) Which of the following materials is used to make a semiconductor?\nA\tSulphur\nB\t**Silicon**\nC\tTantalum\nD\tCopper",
"children": [
{
"content": "> The most basic semiconductor materials are silicon and germanium. Atoms in metallic elements hold their peripheral electrons loosely, such materials make good conductors. Peripheral electrons in non-metallic elements are tightly bound, such materials are insulators. Germanium and silicon fall somewhere between the two categories but are mostly insulators when pure. Doping with impurities increases their conductivity."
}
]
},
{
"content": "A-2-1-1 (D) What two elements widely used in semiconductor devices exhibit both metallic and non-metallic characteristics?\nA\tGalena and germanium\nB\tGalena and bismuth\nC\tSilicon and gold\nD\t**Silicon** and **germanium**",
"children": [
{
"content": "> The most basic semiconductor materials are silicon and germanium. Atoms in metallic elements hold their peripheral electrons loosely, such materials make good conductors. Peripheral electrons in non-metallic elements are tightly bound, such materials are insulators. Germanium and silicon fall somewhere between the two categories but are mostly insulators when pure. Doping with impurities increases their conductivity."
}
]
},
{
"content": "A-2-1-2 (B) In what application is **gallium-arsenide** used as a semiconductor material in preference to germanium or silicon?\nA\tIn bipolar transistors\nB\tAt **microwave frequencies**\nC\tIn high-power circuits\nD\tAt very low frequencies",
"children": [
{
"content": "> Gallium arsenide (GaAs) devices can work at higher frequencies with less noise than their silicon counterparts."
}
]
}
]
},
{
"content": "Pure silicon is an insulator.",
"children": [
{
"content": "A-2-1-7 (A) Silicon, in its pure form, is:\nA\tan insulator\nB\ta superconductor\nC\ta semiconductor\nD\ta conductor",
"children": [
{
"content": "> The most basic semiconductor materials are silicon and germanium. Atoms in metallic elements hold their peripheral electrons loosely, such materials make good conductors. Peripheral electrons in non-metallic elements are tightly bound, such materials are insulators. Germanium and silicon fall somewhere between the two categories but are mostly insulators when pure. Doping with impurities increases their conductivity."
}
]
},
{
"content": "A-2-1-10 (D) Substances such as silicon in a pure state are usually good:\nA\tconductors\nB\ttuned circuits\nC\tinductors\nD\tinsulators",
"children": [
{
"content": "> The most basic semiconductor materials are silicon and germanium. Atoms in metallic elements hold their peripheral electrons loosely, such materials make good conductors. Peripheral electrons in non-metallic elements are tightly bound, such materials are insulators. Germanium and silicon fall somewhere between the two categories but are mostly insulators when pure. Doping with impurities increases their conductivity."
}
]
}
]
},
{
"content": "Adding impurities is called \"**doping**.\"",
"children": [
{
"content": "A-2-1-11 (C) A semiconductor is said to be doped when it has added to it small quantities of:\nA\tions\nB\telectrons\nC\timpurities\nD\tprotons",
"children": [
{
"content": "> Pure germanium and silicon are doped with impurities to produce the basic semiconductor materials. Certain doping impurities add free electrons, forming N-Type material while others accept electrons, thus creating 'holes' found in P-Type material."
}
]
}
]
},
{
"content": "**N-type** silicon contains more electrons than normal.\n\nThe charge carries are electrons.",
"children": [
{
"content": "A-2-1-4 (C) What type of semiconductor material contains more free electrons than pure germanium or silicon crystals?\nA\tBipolar\nB\tSuperconductor\nC\tN-type\nD\tP-type",
"children": [
{
"content": "> Pure germanium and silicon are doped with impurities to produce the basic semiconductor materials. Certain doping impurities add free electrons, forming N-Type material while others accept electrons, thus creating 'holes' found in P-Type material."
}
]
},
{
"content": "A-2-1-6 (B) What are the majority charge carriers in N-type semiconductor material?\nA\tFree neutrons\nB\tFree electrons\nC\tHoles\nD\tFree protons",
"children": [
{
"content": "> N-Type material comprises extra electrons which serve as the electric charge carriers. P-Type material was robbed of free electrons, positive 'holes' are the electric charge carriers."
}
]
}
]
},
{
"content": "**P-type** silicon contains fewer electrons than normal.\n\nThe charge carries are called \"holes.\"",
"children": [
{
"content": "A-2-1-3 (D) What type of semiconductor material contains fewer free electrons than pure germanium or silicon crystals?\nA\tN-type\nB\tBipolar type\nC\tSuperconductor type\nD\tP-type",
"children": [
{
"content": "> Pure germanium and silicon are doped with impurities to produce the basic semiconductor materials. Certain doping impurities add free electrons, forming N-Type material while others accept electrons, thus creating 'holes' found in P-Type material."
}
]
},
{
"content": "A-2-1-5 (D) What are the majority charge carriers in P-type semiconductor material?\nA\tFree electrons\nB\tFree protons\nC\tFree neutrons\nD\tHoles",
"children": [
{
"content": "> P-Type material was robbed of free electrons, positive 'holes' are the electric charge carriers. N-Type material comprises extra electrons which serve as the electric charge carriers."
}
]
}
]
}
]
},
{
"content": "**Diodes**\n\nThere are few types of diodes to know:\n* Point contact **detectors**\n* Varactors with **variable capacitance** (reactance)\n* Schottky **mixers** and detectors\n* PIN **switches**\n* Zener **voltage regulators**",
"children": [
{
"content": "The two main categories of diode are \n\n* **Junction** diodes, and\n* **point contact** diodes.",
"children": [
{
"content": "A-2-2-6 (A) Structurally, what are the two main categories of semiconductor diodes?\nA\t**Junction** and **point contact**\nB\tVacuum and point contact\nC\tElectrolytic and point contact\nD\tElectrolytic and junction",
"children": [
{
"content": "> Point-contact diodes, where a small metal whisker touches the semiconductor material, exhibit low capacitance and serve as RF detectors or UHF mixers. Junction diodes are formed with adjacent blocks of P and N material; these are usable from DC to microwave."
}
]
}
]
},
{
"content": ""
},
{
"content": "Point contact diodes are used as RF detectors.",
"children": [
{
"content": "A-2-2-7 (D) What is a common use for **point contact** diodes?\nA\tAs a constant current source\nB\tAs a constant voltage source\nC\tAs a high voltage rectifier\nD\tAs an RF **detector**",
"children": [
{
"content": "> Point-contact diodes, where a small metal whisker touches the semiconductor material, exhibit low capacitance and serve as RF detectors or UHF mixers. Junction diodes are formed with adjacent blocks of P and N material; these are usable from DC to microwave."
}
]
}
]
},
{
"content": "Aside from the ordinary PN junction diodes used for power rectification, there are also a few other *special* types of junction diodes:"
},
{
"content": ""
},
{
"content": "* [**Varactor** diodes](https://www.google.com/search?q=varicap+diode&tbm=isch&ved=2ahUKEwjqvZrf0ePoAhWHgZ4KHXyzDkEQ2-cCegQIABAA&oq=varicap+diode&gs_lcp=CgNpbWcQAzICCAAyAggAMgIIADIGCAAQBxAeMgYIABAFEB4yBAgAEBgyBAgAEBgyBAgAEBgyBAgAEBgyBAgAEBg6CAgAEAcQBRAeUPMIWMcPYJ8SaABwAHgAgAFPiAH9A5IBATeYAQCgAQGqAQtnd3Mtd2l6LWltZw&sclient=img&ei=LW6TXqrzAYeD-gT85rqIBA&bih=567&biw=1024&hl=en) vary their capacitance in relation to voltage. (Think *var* - variable and *ractor* - reactance.) (Used in e.g. tuning circuits.) ",
"children": [
{
"content": "A-2-2-2 (C) What type of semiconductor diode **varies** its internal **capacitance** as the voltage applied to its terminals varies?\nA\tSilicon-controlled rectifier\nB\tHot-carrier (Schottky)\nC\t**Varactor**\nD\tZener",
"children": [
{
"content": "> Zener diodes maintain a constant voltage across a range of currents. The Varactor (or Varicap) is a diode used under reverse bias as a \"voltage-variable capacitor\". Hot-carrier (or Schottky-barrier) diodes have lower forward voltage and good high-frequency response: their speed make them useful in Very High Frequency mixers or detectors; in power circuits, they are excellent rectifiers in switching power supplies. PIN diodes (with a layer of undoped or lightly doped 'intrinsic' silicon between the P and N regions) are used as switches or attenuators."
}
]
}
]
},
{
"content": "* **Schottky** diodes are used [in mixers](https://www.google.com/search?q=schottky+diode+mixer&tbm=isch&ved=2ahUKEwjUwevg0ePoAhU1lZ4KHefwBD8Q2-cCegQIABAA&oq=schottky+diode+mixer&gs_lcp=CgNpbWcQAzIECAAQGDoECAAQQzoCCAA6BQgAEIMBOgYIABAFEB46BggAEAoQGDoECAAQHlC7kwlYs7sJYLy9CWgEcAB4AIABVIgB6g2SAQIyNJgBAKABAaoBC2d3cy13aXotaW1n&sclient=img&ei=MG6TXtTpG7Wq-gTn4ZP4Aw&bih=567&biw=1024&hl=en) and [detectors](https://www.google.com/search?q=schottky+diode+detector&tbm=isch&ved=2ahUKEwjny4LP0uPoAhXdAjQIHfwXAc0Q2-cCegQIABAA&oq=schottky+diode+detector&gs_lcp=CgNpbWcQAzICCAAyBggAEAgQHjIECAAQGDoECAAQQ1DdvAtYu8ULYPXHC2gAcAB4AIABV4gB2gSSAQE4mAEAoAEBqgELZ3dzLXdpei1pbWc&sclient=img&ei=F2-TXqfkH92F0PEP_K-E6Aw&bih=567&biw=1024&hl=en).\n\n![](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Schottky_diode_symbol.svg/110px-Schottky_diode_symbol.svg.png)",
"children": [
{
"content": "A-2-2-3 (D) What is a common use for the hot-carrier (Schottky) diode?\nA\tAs balanced mixers in FM generation\nB\tAs a variable capacitance in an automatic frequency control (AFC) circuit\nC\tAs a constant voltage reference in a power supply\nD\tAs VHF and UHF **mixers and detectors**",
"children": [
{
"content": "> Zener diodes maintain a constant voltage across a range of currents. The Varactor (or Varicap) is a diode used under reverse bias as a \"voltage-variable capacitor\". Hot-carrier (or Schottky-barrier) diodes have lower forward voltage and good high-frequency response: their speed make them useful in Very High Frequency mixers or detectors; in power circuits, they are excellent rectifiers in switching power supplies. PIN diodes (with a layer of undoped or lightly doped 'intrinsic' silicon between the P and N regions) are used as switches or attenuators."
}
]
}
]
},
{
"content": "* **PIN** diodes are used as RF switches.\n\n(Used to mute or protect the front-end of a receiver when, e.g. in the presence of a receiver. As opposed to, say, relays.)",
"children": [
{
"content": "A-2-2-8 (D) What is one common use for **PIN diodes**?\nA\tAs a constant current source\nB\tAs a high voltage rectifier\nC\tAs a constant voltage source\nD\tAs an **RF switch**",
"children": [
{
"content": "> Zener diodes maintain a constant voltage across a range of currents. The Varactor (or Varicap) is a diode used under reverse bias as a \"voltage-variable capacitor\". Hot-carrier (or Schottky-barrier) diodes have lower forward voltage and good high-frequency response: their speed make them useful in Very High Frequency mixers or detectors; in power circuits, they are excellent rectifiers in switching power supplies. PIN diodes (with a layer of undoped or lightly doped 'intrinsic' silicon between the P and N regions) are used as switches or attenuators."
}
]
}
]
},
{
"content": "* **Zener** diodes have a precise and constant forward voltage that is used in **voltage regulator** circuits.\n\n![](https://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Zener_diode_symbol-2.svg/55px-Zener_diode_symbol-2.svg.png)",
"children": [
{
"content": "A-2-2-9 (D) A Zener diode is a device used to:\nA\tdissipate voltage\nB\tdecrease current\nC\tincrease current\nD\t**regulate voltage**",
"children": [
{
"content": "> Zener diodes maintain a constant voltage across a range of currents. The Varactor (or Varicap) is a diode used under reverse bias as a \"voltage-variable capacitor\". Hot-carrier (or Schottky-barrier) diodes have lower forward voltage and good high-frequency response: their speed make them useful in Very High Frequency mixers or detectors; in power circuits, they are excellent rectifiers in switching power supplies. PIN diodes (with a layer of undoped or lightly doped 'intrinsic' silicon between the P and N regions) are used as switches or attenuators."
}
]
},
{
"content": "A-2-2-1 (C) What is the principal characteristic of a Zener diode?\nA\tA negative resistance region\nB\tAn internal capacitance that varies with the applied voltage\nC\tA **constant voltage** under conditions of **varying current**\nD\tA constant current under conditions of varying voltage",
"children": [
{
"content": "> Zener diodes maintain a constant voltage across a range of currents. The Varactor (or Varicap) is a diode used under reverse bias as a \"voltage-variable capacitor\". Hot-carrier (or Schottky-barrier) diodes have lower forward voltage and good high-frequency response: their speed make them useful in Very High Frequency mixers or detectors; in power circuits, they are excellent rectifiers in switching power supplies. PIN diodes (with a layer of undoped or lightly doped 'intrinsic' silicon between the P and N regions) are used as switches or attenuators."
}
]
}
]
},
{
"content": "The major ratings of junction diodes are:\n* Maximum **forward current**, and\n* **peak inverse voltage** (PIV).",
"children": [
{
"content": "A-2-2-5 (D) What are the major ratings for junction diodes?\nA\tMaximum reverse current and capacitance\nB\tMaximum forward current and capacitance\nC\tMaximum reverse current and peak inverse voltage (PIV)\nD\tMaximum **forward current** and peak **inverse voltage** (PIV)",
"children": [
{
"content": "> Diodes conduct in one direction only: under forward bias, maximum forward current is limited by acceptable junction temperature. The voltage drop across the junction (volts) multiplied by the forward current (amperes) gives rise to heat dissipation (watts). Surviving a reverse bias is determined by the Peak Inverse Voltage (PIV) rating."
}
]
},
{
"content": "A-2-2-4 (C) What **limits** the maximum forward current in a junction diode?\nA\tBack EMF\nB\tPeak inverse voltage\nC\tJunction **temperature**\nD\tForward voltage",
"children": [
{
"content": "> Diodes conduct in one direction only: under forward bias, maximum forward current is limited by acceptable junction temperature. The voltage drop across the junction (volts) multiplied by the forward current (amperes) gives rise to heat dissipation (watts). Surviving a reverse bias is determined by the Peak Inverse Voltage (PIV) rating."
}
]
}
]
},
{
"content": "At the PN junction, a thin depletion layer forms, across which an intrinsic voltage drop occurs.\n\nCurrent flowing across this voltage drop dissipates power, resulting in heat.\n\nTheir forward current is **limited by temperature**, which is due to the power dissipated by the intrinsic voltage drop across the depletion layer. The layer can only dissipate so much heat before failing.",
"children": [
{
"content": "A-2-2-11 (C) The power-handling capability of most Zener diodes is rated at 25 degrees C or approximately room temperature. If the temperature is increased, the power handling capability is:\nA\tmuch greater\nB\tslightly greater\nC\tless\nD\tthe same",
"children": [
{
"content": "> Heat flows from hot to cold. If ambient temperature is higher, less heat can be drained from the junction, the junction will reach maximum safe operating temperature quicker."
}
]
},
{
"content": "A-2-2-10 (D) If a Zener diode rated at 10 V and 50 watts was operated at maximum dissipation rating, it would conduct ____ amperes:\nA\t50\nB\t0.05\nC\t0.5\nD\t5",
"children": [
{
"content": "> P = E times I. Watts = volts times amperes. Thus, I = P divided by E: 50 watts divided by 10 volts = 5 amperes."
}
]
}
]
}
]
},
{
"content": "**Transistors**\n\nThe two types of transistors of interest here are:\n\n* Bipolar junction transistors (BJTs), and\n* Field-effect transistors (FETs) including junction FETs (JFETS) and MOSFETS.",
"children": [
{
"content": "The distinction between BJTs and FETs has to do with input impedance; that is, how much current they draw for a given control voltage.",
"children": [
{
"content": "* BJTs have **low** input (gate) impedance and therefore consume a lot of current to operate at a given voltage.\n* FETs have **high** input impedance, and consume little current for the same voltage.",
"children": [
{
"content": "A-2-4-5 (A) How does the input impedance of a field-effect transistor (FET) compare with that of a bipolar transistor?\nA\tAn FET has **high input impedance**; a bipolar transistor has **low input impedance**\nB\tOne cannot compare input impedance without knowing supply voltage\nC\tAn FET has low input impedance; a bipolar transistor has high input impedance\nD\tThe input impedance of FETs and bipolar transistors is the same",
"children": [
{
"content": "> Bipolar transistors are operated with a forward-biased (conductive) Base-Emitter junction. Bipolar transistors are current amplifiers. Impedance, as a ratio of voltage to current, is necessarily low when voltage is low and current is high. The Field Effect Transistor, with a reverse biased Gate to channel junction, and the Insulated Gate Field Effect Transistor (IGFET or metal-oxide-semiconductor FET, MOSFET) with a Gate separated from the channel by a dielectric, are high impedance devices."
}
]
}
]
}
]
},
{
"content": "**BJT\n**\nThe middle letter indicates the polarity of the activating voltage.\n\nThe figure of merit for the common-b**a**se configuration is **a**lpha.\n\nThe figure of merit for the common-**e**mitter or common-collector configurations is b**e**ta.",
"children": [
{
"content": "There are two types of BJTs; PNP and NPN. The middle letter refers to the base, which responds to voltage of the same polarity:\n* The N**P**N likes to get tickled by **positive** voltage, and\n* the P**N**P likes to get tickled by **negative** voltage.",
"children": [
{
"content": "A-2-3-3 (D) Which component conducts electricity from a negative emitter to a positive collector when its **base** voltage is made **positive**?\nA\tA varactor\nB\tA triode vacuum tube\nC\tA PNP transistor\nD\tAn **NPN** transistor",
"children": [
{
"content": "> The terms Emitter, Collector and Base refer to bipolar transistors, of which there are two types: NPN and PNP. The Base-Emitter junction must be forward-biased for Base current to exist. A positive voltage on the Base supposes P material for conduction to take place, the 'sandwich' is thus NPN. Inversely, a negative Base voltage relates to a PNP."
}
]
},
{
"content": "A-2-3-8 (C) Which component conducts electricity from a positive emitter to a negative collector when its **base** is made **negative**?\nA\tA varactor\nB\tAn NPN transistor\nC\tA **PNP** transistor\nD\tA triode vacuum tube",
"children": [
{
"content": "> The terms Emitter, Collector and Base refer to bipolar transistors, of which there are two types: NPN and PNP. The Base-Emitter junction must be forward-biased for Base current to exist. A positive voltage on the Base supposes P material for conduction to take place, the 'sandwich' is thus NPN. Inversely, a negative Base voltage relates to a PNP."
}
]
}
]
},
{
"content": "There are two BJT configurations of interest:\n* [common base](https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/transistors/bipolarjunctiontransistor/commonbaseconfiguration.html), and\n* [common emitter](https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/transistors/bipolarjunctiontransistor/commonemitterconfiguration.html) and [common collector](https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/transistors/bipolarjunctiontransistor/commoncollectorconfiguration.html)\n\nFor the purpose of the exam, the parameter of interest in both cases is the **current gain** (*alpha* and *beta*).\n",
"children": [
{
"content": "The **forward current gain** *alpha* is specified for the **common base** configuration. In this configuration, the emitter is the control terminal (?). \n\n\nThe quantity describes how much **collector** (output) current you get for how much **emitter** (control) current, which is mathematically:\n````\n d I_c \nalpha = -----\n d I_e\n````\n\n\n\n*Alpha* is related to *beta* by:\n```\n beta\nalpha = ----------\n (1 + beta)\n```",
"children": [
{
"content": "A-2-3-4 (A) What is the alpha of a bipolar transistor in common base configuration?\nA\t**Forward current gain**\nB\tForward voltage gain\nC\tReverse current gain\nD\tReverse voltage gain",
"children": [
{
"content": "> The Alpha being a number smaller than 1, many authors refer to it as the \"common base forward current transfer ratio\" rather than a gain. In a 'common base' configuration where the Emitter is the input and the Collector is the output, the Alpha factor (or common base forward current transfer ratio) is a ratio of a change in Collector current to the corresponding change in Emitter current. In a 'common emitter' configuration where the Base is the input and the Collector is the output, the Beta factor (or common emitter forward current gain) is a ratio of a change in Collector current to a given change in Base current. The Beta factor applies equally to a Common Collector configuration where the Base is also the input."
}
]
},
{
"content": "A-2-3-6 (D) The alpha of a bipolar transistor is specified for what configuration?\nA\tCommon collector\nB\tCommon gate\nC\tCommon emitter\nD\t**Common base**",
"children": [
{
"content": "> In a 'common base' configuration where the Emitter is the input and the Collector is the output, the Alpha factor (or common base forward current transfer ratio) is a ratio of a change in Collector current to the corresponding change in Emitter current. In a 'common emitter' configuration where the Base is the input and the Collector is the output, the Beta factor (or common emitter forward current gain) is a ratio of a change in Collector current to a given change in Base current. The Beta factor applies equally to a Common Collector configuration where the Base is also the input."
}
]
},
{
"content": "A-2-3-1 (C) What is the alpha of a bipolar transistor?\nA\tThe change of base current with respect to collector current\nB\tThe change of collector current with respect to gate current\nC\tThe change of **collector current** with respect to **emitter current**\nD\tThe change of collector current with respect to base current",
"children": [
{
"content": "> In a 'common base' configuration where the Emitter is the input and the Collector is the output, the Alpha factor (or common base forward current transfer ratio) is a ratio of a change in Collector current to the corresponding change in Emitter current. In a 'common emitter' configuration where the Base is the input and the Collector is the output, the Beta factor (or common emitter forward current gain) is a ratio of a change in Collector current to a given change in Base current. The Beta factor applies equally to a Common Collector configuration where the Base is also the input."
}
]
},
{
"content": "A-2-3-9 (B) Alpha of a bipolar transistor is equal to:\nA\tbeta / (1 - beta)\nB\t**beta / (1 + beta)**\nC\tbeta x (1 + beta)\nD\tbeta x (1 - beta)",
"children": [
{
"content": "> Alpha ('common base') is always a number lesser than 1 ( the Emitter current is necessarily larger than the Collector current because the Base current also flows through the Emitter ). Beta ('common emitter') is normally a number greater than 10 ( the Collector current is always several times the Base current ). The Alpha is equal to Beta divided by 1 plus Beta. The Beta is equal to Alpha divided by 1 minus Alpha."
}
]
}
]
},
{
"content": "Common emitter and common collector\n\nCommon emitter:\n```\nemitter o +V \n |\nbase N \n +V o-----P\n N\n |\ncollector o -V\n```"
},
{
"content": "In the more typical **common emitter** or **common collector** configuration, the **base** is the control terminal, and the forward current gain is called ***beta***.\n\n(Think: * **b**ase*, * **b**eta*)",
"children": [
{
"content": "A-2-3-7 (A) The beta of a bipolar transistor is specified for what configurations?\nA\tCommon **emitter** or common **collector**\nB\tCommon emitter or common gate\nC\tCommon base or common collector\nD\tCommon base or common emitter",
"children": [
{
"content": "> In a 'common base' configuration where the Emitter is the input and the Collector is the output, the Alpha factor (or common base forward current transfer ratio) is a ratio of a change in Collector current to the corresponding change in Emitter current. In a 'common emitter' configuration where the Base is the input and the Collector is the output, the Beta factor (or common emitter forward current gain) is a ratio of a change in Collector current to a given change in Base current. The Beta factor applies equally to a Common Collector configuration where the Base is also the input."
}
]
}
]
},
{
"content": "The quantity describes how much **collector** (output) current you get for how much **base** (control) current, which is mathematically:\n\n````\n d I_c \nbeta = -----\n d I_b\n````",
"children": [
{
"content": "A-2-3-2 (C) What is the **beta** of a bipolar transistor?\nA\tThe change of collector current with respect to emitter current\nB\tThe change of base current with respect to gate current\nC\tThe change of **collector** current with respect to **base** current\nD\tThe change of base current with respect to emitter current",
"children": [
{
"content": "> In a 'common base' configuration where the Emitter is the input and the Collector is the output, the Alpha factor (or common base forward current transfer ratio) is a ratio of a change in Collector current to the corresponding change in Emitter current. In a 'common emitter' configuration where the Base is the input and the Collector is the output, the Beta factor (or common emitter forward current gain) is a ratio of a change in Collector current to a given change in Base current. The Beta factor applies equally to a Common Collector configuration where the Base is also the input."
}
]
},
{
"content": "A-2-3-5 (C) In a bipolar transistor, the change of **collector** current with respect to **base** current is called:\nA\tdelta\nB\talpha\nC\t**beta**\nD\tgamma",
"children": [
{
"content": "> In a 'common base' configuration where the Emitter is the input and the Collector is the output, the Alpha factor (or common base forward current transfer ratio) is a ratio of a change in Collector current to the corresponding change in Emitter current. In a 'common emitter' configuration where the Base is the input and the Collector is the output, the Beta factor (or common emitter forward current gain) is a ratio of a change in Collector current to a given change in Base current. The Beta factor applies equally to a Common Collector configuration where the Base is also the input."
}
]
}
]
},
{
"content": "*Beta* is related to *alpha* by:\n```\n alpha\nbeta = ----------\n (1 - alpha)\n```",
"children": [
{
"content": "A-2-3-11 (C) Beta of a bipolar transistor is equal to:\nA\talpha x (1 - alpha)\nB\talpha x (1 + alpha)\nC\t**alpha / (1 - alpha)**\nD\talpha / (1 + alpha)",
"children": [
{
"content": "> Alpha ('common base') is always a number lesser than 1 ( the Emitter current is necessarily larger than the Collector current because the Base current also flows through the Emitter ). Beta ('common emitter') is normally a number greater than 10 ( the Collector current is always several times the Base current ). The Alpha is equal to Beta divided by 1 plus Beta. The Beta is equal to Alpha divided by 1 minus Alpha."
}
]
}
]
},
{
"content": "*Alpha* is less than one. *Beta* is greater than ten.",
"children": [
{
"content": "A-2-3-10 (B) The current gain of a bipolar transistor in common emitter or common collector compared to common base configuration is:\nA\tusually about half\nB\t**high to very high**\nC\tvery low\nD\tusually about double",
"children": [
{
"content": "> Alpha ('common base') is always a number lesser than 1 ( the Emitter current is necessarily larger than the Collector current because the Base current also flows through the Emitter ). Beta ('common emitter') is normally a number greater than 10 ( the Collector current is always several times the Base current ). The Alpha is equal to Beta divided by 1 plus Beta. The Beta is equal to Alpha divided by 1 minus Alpha."
}
]
}
]
}
]
}
]
},
{
"content": "**FET**\n\nThe terminals are **source**, **gate**, and **drain**.\n\nThey act in **enhancement**-mode or **depletion** mode, akin to normally-on or normally-off.\n\nThey type determines the charge carriers: **N**-channel types support **electron**-conduction, and **P**-channel supports hole-conduction.",
"children": [
{
"content": "The terminals of a FET are source, gate, and drain. The gate is the control terminal.",
"children": [
{
"content": "A-2-4-6 (B) What are the three terminals of a junction field-effect transistor (JFET)?\nA\tGate 1, gate 2, drain\nB\t**Gate, drain, source**\nC\tEmitter, base 1, base 2\nD\tEmitter, base, collector",
"children": [
{
"content": "> Remember your Basic Qualification? The FET comprises a Source, a Gate and a Drain. They come in two types: N-Channel and P-Channel."
}
]
}
]
},
{
"content": "FETs act either in **enhancement-mode** or **depletion-mode**, depending on whether the conduction channel is enhanced or depleted by the application of a control voltage.",
"children": [
{
"content": "In an enhancement-mode FET, initially there is **no** channel. The channel is established (*enhanced*) by the application of voltage. (I.e., normally-off.)",
"children": [
{
"content": "A-2-4-1 (A) What is an **enhancement-mode** FET?\nA\tAn FET **without a channel**; **no current** occurs with zero gate voltage\nB\tAn FET with a channel that blocks voltage through the gate\nC\tAn FET with a channel that allows current when the gate voltage is zero\nD\tAn FET without a channel to hinder current through the gate",
"children": [
{
"content": "> An Enhancement-mode Insulated Gate Field Effect Transistor (IGFET) is constructed without a channel. There is no Drain current with zero Gate voltage. A voltage applied to the gate leads to the creation of a channel. A forward bias on the gate heightens the concentration of charge carriers which, in turn, 'enhances' conduction. A Depletion-mode Insulated Gate Field Effect Transistor has a channel. Drain current is possible even without a Gate voltage. A reverse bias on the Gate depletes charge carriers in the channel, thus reducing Drain current. A forward bias on the Gate can make the channel even more conductive."
}
]
}
]
},
{
"content": "In a depletion mode FET, initially there is a channel that is *depleted* by the application of voltage. (I.e., normally-on.)",
"children": [
{
"content": "A-2-4-2 (B) What is a **depletion-mode** FET?\nA\tAn FET that has a channel that blocks current when the gate voltage is zero\nB\tAn FET that **has a channel** with **no gate voltage** applied; a **current flows** with zero gate voltage\nC\tAn FET without a channel; no current flows with zero gate voltage\nD\tAn FET without a channel to hinder current through the gate",
"children": [
{
"content": "> An Enhancement-mode Insulated Gate Field Effect Transistor (IGFET) is constructed without a channel. There is no Drain current with zero Gate voltage. A voltage applied to the gate leads to the creation of a channel. A forward bias on the gate heightens the concentration of charge carriers which, in turn, 'enhances' conduction. A Depletion-mode Insulated Gate Field Effect Transistor has a channel. Drain current is possible even without a Gate voltage. A reverse bias on the Gate depletes charge carriers in the channel, thus reducing Drain current. A forward bias on the Gate can make the channel even more conductive."
}
]
}
]
}
]
},
{
"content": "FETs come in **N-channel** and **P-channel**, which determine the polarity of the ON or OFF states dependent on the configuration.",
"children": [
{
"content": "A-2-4-7 (A) What are the two basic types of junction field-effect transistors (JFET)?\nA\t**N-channel and P-channel**\nB\tHigh power and low power\nC\tMOSFET and GaAsFET\nD\tSilicon and germanium",
"children": [
{
"content": "> Remember your Basic Qualification? The FET comprises a Source, a Gate and a Drain. They come in two types: N-Channel and P-Channel."
}
]
}
]
},
{
"content": "P-channel (MOS)FETs support **hole conduction**, in either-[enhancement mode or depletion-mode](https://en.wikipedia.org/wiki/Depletion_and_enhancement_modes).",
"children": [
{
"content": "A-2-4-10 (A) **Hole conduction** in a p-channel depletion type MOSFET is associated with:\nA\t**p-channel depletion**\nB\tn-channel enhancement\nC\tq-channel depletion\nD\tn-channel depletion",
"children": [
{
"content": "> This seems too simple to be true, the words in the question give the answer away."
}
]
},
{
"content": "A-2-4-11 (D) **Hole conduction** in a **p**-channel **enhancement** type MOSFET is associated with:\nA\tn-channel depletion\nB\tn-channel enhancement\nC\tq-channel depletion\nD\t**p-channel enhancement**",
"children": [
{
"content": "> This seems too simple to be true, the words in the question give the answer away."
}
]
}
]
},
{
"content": "N-channel (MOS)FETs support **electron conduction**, in either [enhancement mode or depletion-mode](https://en.wikipedia.org/wiki/Depletion_and_enhancement_modes).",
"children": [
{
"content": "A-2-4-9 (D) **Electron conduction** in an **n-channel** enhancement MOSFET is associated with:\nA\tq-channel depletion\nB\tp-channel enhancement\nC\tp-channel depletion\nD\tn-channel **enhancement**",
"children": [
{
"content": "> This seems too simple to be true, the words in the question give the answer away."
}
]
},
{
"content": "A-2-4-8 (D) **Electron conduction** in an **n-channel** depletion type MOSFET is associated with:\nA\tp-channel depletion\nB\tp-channel enhancement\nC\tq-channel enhancement\nD\tn-channel **depletion**",
"children": [
{
"content": "> This seems too simple to be true, the words in the question give the answer away."
}
]
}
]
},
{
"content": "**MOSFET** gates are sensitive to ESD, and include Zener diodes to protect them.",
"children": [
{
"content": "A-2-4-4 (D) Why are special precautions necessary in handling FET and **CMOS** devices?\nA\tThey are light-sensitive\nB\tThey have micro-welded semiconductor junctions that are susceptible to breakage\nC\tThey have fragile leads that may break off\nD\tThey are susceptible to **damage from static charges**",
"children": [
{
"content": "> The Gate in an Insulated Gate Field Effect Transistor (IGFET or metal-oxide-semiconductor FET, MOSFET) is insulated from the channel by a thin oxide layer. Static electricity or excessive voltage can easily destroy the dielectric layer."
}
]
},
{
"content": "A-2-4-3 (B) Why do many MOSFET devices have built-in gate protective Zener diodes?\nA\tThe gate-protective Zener diode provides a voltage reference to provide the correct amount of reverse-bias gate voltage\nB\tThe gate-protective Zener diode prevents the gate insulation from being punctured by small **static charges** or excessive voltages\nC\tThe gate-protective Zener diode keeps the gate voltage within specifications to prevent the device from overheating\nD\tThe gate-protective Zener diode protects the substrate from excessive voltages",
"children": [
{
"content": "> The Gate in an Insulated Gate Field Effect Transistor (IGFET or metal-oxide-semiconductor FET, MOSFET) is insulated from the channel by a thin oxide layer. Static electricity or excessive voltage can easily destroy the dielectric layer."
}
]
}
]
}
]
}
]
},
{
"content": "Transistor-Like Diodes\n\n**Silicon Controlled-Rectifiers** are three-terminal, diode-like switches.",
"children": [
{
"content": "The SCR is a type of [thyristor](https://en.wikipedia.org/wiki/Thyristor), which is made from four layers of doped silcon forming a **PNPN** junction. (\"The big mac of diodes.\")",
"children": [
{
"content": "A-2-5-7 (D) The silicon controlled rectifier (SCR) is a member of which family?\nA\tPhase locked loops\nB\tVaractors\nC\tVaristors\nD\t**Thyristors**",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
},
{
"content": "A-2-5-5 (D) The silicon controlled rectifier (SCR) is what type of device?\nA\tNPPN\nB\tPNNP\nC\tPPNN\nD\t**PNPN**",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
},
{
"content": "A-2-5-11 (B) Which of the following is a **PNPN** device?\nA\tZener diode\nB\tSilicon controlled rectifier (**SCR**)\nC\tPIN diode\nD\tHot carrier (Schottky) diode",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
}
]
},
{
"content": "They are used in [**crowbar** circuits](https://www.google.com/search?q=scr+crowbar+circuit&tbm=isch&ved=2ahUKEwj6y_Gp0-PoAhU1h54KHcODDlYQ2-cCegQIABAA&oq=scr+crow&gs_lcp=CgNpbWcQARgBMgIIADICCAAyBggAEAgQHjIECAAQGDIECAAQGDoECAAQQzoFCAAQgwFQ5oUGWJiOBmDrlQZoAHAAeACAAVaIAesEkgEBOJgBAKABAaoBC2d3cy13aXotaW1n&sclient=img&ei=1m-TXvqIBbWO-gTDh7qwBQ&bih=567&biw=1024&hl=en) for **overvoltage protection**, in conjunction with a zener diode to set the trigger voltage.\n",
"children": [
{
"content": "A-2-5-8 (C) In amateur radio equipment, which is the major application for the silicon controlled rectifier (SCR)?\nA\tMicrophone preamplifier circuit\nB\tSWR detector circuit\nC\tPower supply overvoltage \"crowbar\" circuit\nD\tClass C amplifier circuit",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
}
]
},
{
"content": "The three terminals are anode, cathode, and gate. The **gate** is the control terminal.",
"children": [
{
"content": "A-2-5-1 (D) What are the three terminals of a silicon controlled rectifier (SCR)?\nA\tGate, base 1 and base 2\nB\tBase, collector and emitter\nC\tGate, source and sink\nD\tAnode, cathode and gate",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
},
{
"content": "A-2-5-9 (A) Which of the following devices has anode, cathode, and gate?\nA\tThe silicon controlled rectifier (SCR)\nB\tThe bipolar transistor\nC\tThe field effect transistor\nD\tThe triode vacuum tube",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
},
{
"content": "A-2-5-6 (B) The control element in the silicon controlled rectifier (SCR) is called the:\nA\temitter\nB\tgate\nC\tanode\nD\tcathode",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
}
]
},
{
"content": "The two stable states are **conducting** and **non-conducting**.",
"children": [
{
"content": "A-2-5-2 (C) What are the two stable operating conditions of a silicon controlled rectifier (SCR)?\nA\tNPN conduction and PNP conduction\nB\tOscillating and quiescent\nC\t**Conducting** and **non-conducting**\nD\tForward conducting and reverse conducting",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
}
]
},
{
"content": "Most of the time, they do not conduct; however, if there's an overvoltage across the diode, it will conduct.\n\nWhen [**triggered** or gated on](https://www.youtube.com/watch?v=T7H97vCgEVI) (i.e. conducting), they appear like a forward-biased junction or rectifier diode.",
"children": [
{
"content": "A-2-5-3 (D) When a silicon controlled rectifier (SCR) is **triggered**, to what other semiconductor diode are its electrical characteristics similar (as measured between its cathode and anode)?\nA\tThe PIN diode\nB\tThe hot-carrier (Schottky) diode\nC\tThe varactor diode\nD\tThe **junction diode**",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
},
{
"content": "A-2-5-4 (C) Under what operating condition does a silicon controlled rectifier (SCR) exhibit electrical characteristics similar to a **forward-biased silicon rectifier**?\nA\tWhen it is used as a detector\nB\tDuring a switching transition\nC\tWhen it is **gated \"on\"**\nD\tWhen it is gated \"off\"",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
},
{
"content": "A-2-5-10 (D) When it is gated \"on\", the silicon controlled rectifier (SCR) exhibits electrical characteristics similar to a:\nA\treverse-biased silicon rectifier\nB\tforward-biased PIN diode\nC\treverse-biased hot-carrier (Schottky) diode\nD\t**forward-biased silicon rectifier**",
"children": [
{
"content": "> The SCR, part of the Thyristor family, is made of four layers of alternating P and N type material, namely PNPN. It comprises three electrodes: Anode, Gate and Cathode. As can be expected, the two outermost electrodes, the Anode and the Cathode are respectively type P and type N material. Without gate current, the SCR looks like a regular non-conducting junction diode. Once triggered via the Gate, the SCR resembles a forward-biased (conducting) junction diode. Conduction continues unless current falls below a critical level. One typical application is an overvoltage protection circuit in a power supply."
}
]
}
]
}
]
}
]
},
{
"content": "\n{L04} Power Supplies.",
"children": [
{
"content": "block diagram",
"children": [
{
"content": "A-4-4-10 (C) In a regulated power supply, the output of the electrolytic filter capacitor is connected to the:\nA\tsolid-state by-pass circuit\nB\tmatching circuit for the load\nC\tvoltage regulator\nD\tpi filter",
"children": [
{
"content": "> Remember your Basic Qualification? The Regulated Power Supply comprises: the input, the transformer, the rectifier, the filter, the regulator and the output."
}
]
}
]
},
{
"content": "**Fuses** are placed before the transformer, and before the output.",
"children": [
{
"content": "A-4-4-9 (B) In a regulated power supply, components that conduct alternating current at the input **before the transformer** and direct current **before the output** are:\nA\tchokes\nB\tfuses\nC\tcapacitors\nD\tdiodes",
"children": [
{
"content": "> Only fuses can be expected to be found on either side of the transformer and pass AC or DC equally."
}
]
}
]
},
{
"content": "rectifiers",
"children": [
{
"content": "The full-wave center-tap toplogy rectifier is somewhat inferior to the full-wave bridge topology.",
"children": [
{
"content": "A-4-1-1 (D) For the same transformer secondary voltage, which rectifier has the **highest average output voltage**?\n~~A\tHalf-wave~~\n~~B\tQuarter-wave~~\nC\tFull-wave centre-tap\nD\t**Bridge**",
"children": [
{
"content": "> The half-wave configuration is not as efficient at rectification as the full-wave. The real choice lies between the two full-wave alternatives: **bridge** or **full-wave with centre-tap**. The bridge configuration rectifies the full secondary winding voltage. In contrast, the two-diode with centre-tapped transformer secondary **only rectifies half the secondary voltage on each half-cycle**."
}
]
}
]
},
{
"content": "A-4-1-4 (A) A full-wave bridge rectifier circuit makes use of both halves of the AC cycle, but unlike the full-wave centre-tap rectifier circuit it does not require:\nA\ta centre-tapped secondary on the transformer\nB\tany output filtering\nC\ta centre-tapped primary on the transformer\nD\tdiodes across each leg of the transformer",
"children": [
{
"content": "> A four-diode bridge rectifier makes use of the full secondary winding without the need for a centre-tap."
}
]
},
{
"content": "A-4-1-3 (B) In a full-wave centre-tap power supply, regardless of load conditions, the peak inverse voltage (PIV) will be _____ times the RMS voltage:\nA\t1.4\nB\t2.8\nC\t0.636\nD\t0.707",
"children": [
{
"content": "> With the RMS voltage defined in this example as the voltage from one extremity of the secondary winding to the centre-tap, each diode is subjected to 2.8 times the RMS voltage, peak reverse voltage from half the transformer winding adds to the peak DC output as a reverse bias on the diode during non-conduction ( each diode serves as a half-wave rectifier )."
}
]
},
{
"content": "A-4-4-8 (C) In a regulated power supply, four diodes connected together in a BRIDGE act as:\nA\tmatching between the secondary of the power transformer and the filter\nB\ta tuning network\nC\ta rectifier\nD\tequalization across the transformer\n> Four diodes in a bridge configuration permit full-wave rectification with a single secondary winding."
}
]
},
{
"content": "full-wave center-tap"
},
{
"content": "half-wave supply",
"children": [
{
"content": "A-4-1-2 (A) In a half-wave power supply with a capacitor input filter and a load drawing little or no current, the peak inverse voltage (PIV) across the diode can reach _____ times the RMS voltage.\nA\t2.8\nB\t0.45\nC\t5.6\nD\t1.4",
"children": [
{
"content": "> During conduction, the capacitor charges up to the peak value of the waveform (1.4 times the RMS value). On the opposite half-cycle, and from the diode's standpoint, the transformer winding reaching opposite peak value (1.4 times the RMS value) adds to the capacitor charge for a total of 2.8 times the RMS value."
}
]
}
]
},
{
"content": "full-wave",
"children": [
{
"content": "A-4-1-6 (B) The ripple frequency produced by a full-wave power supply connected to a normal household circuit is:\nA\t30 Hz\nB\t120 Hz\nC\t60 Hz\nD\t90 Hz",
"children": [
{
"content": "> Key word: FULL-WAVE. The two half-cycles are put to contribution. The output goes from zero to peak and back 120 times per second. Half-wave would be 60 hertz."
}
]
},
{
"content": "A-4-1-5 (A) For a given transformer the maximum output voltage available from a full-wave bridge rectifier circuit will be:\nA\tdouble that of the full-wave centre-tap rectifier\nB\thalf that of the full-wave centre-tap rectifier\nC\tthe same as the full-wave centre-tap rectifier\nD\tthe same as the half-wave rectifier",
"children": [
{
"content": "> The discussion relates to rectification, thus DC voltage output is the criteria. Imagine a 12 volts AC secondary with a centre tap. A bridge rectifier across the full secondary will obviously provide twice the voltage of a full-wave centre-tap rectifier where each diode draws from half the secondary. The bridge rectifier will also output slightly more DC voltage after filtering than a half-wave rectifier across the same full secondary."
}
]
}
]
},
{
"content": "half-wave supply",
"children": [
{
"content": "A-4-1-7 (A) The ripple frequency produced by a half-wave power supply connected to a normal household circuit is:\nA\t60 Hz\nB\t90 Hz\nC\t120 Hz\nD\t30 Hz",
"children": [
{
"content": "> Key word: HALF-WAVE. One half-cycle only is put to contribution. The output goes from zero to peak and back 60 times per second. Full-wave would be 120 hertz."
}
]
}
]
},
{
"content": "voltage doubler",
"children": [
{
"content": "A-4-1-8 (A) Full-wave voltage doublers:\nA\tuse both halves of an AC wave\nB\tcreate four times the output voltage of half-wave doublers\nC\tuse less power than half-wave doublers\nD\tare used only in high-frequency power supplies\n> A voltage doubler returns a DC voltage approximately twice the supplied AC voltage. Through combinations of diodes and capacitors, both half-cycles are rectified and added together. Two ubiquitous configurations are respectively designated as \"half-wave\" doubler and \"full-wave\" doubler. The designation has more to do with the ripple frequency than how energy is transferred to the output. Ripple frequency in the \"full-wave\" doubler is twice the supply frequency. They can be implemented at normal line frequency or in switching power supplies."
}
]
},
{
"content": "diode specifications",
"children": [
{
"content": "A-4-1-9 (D) What are the two major ratings that must not be exceeded for silicon-diode rectifiers used in power-supply circuits?\nA\tAverage power; average voltage\nB\tCapacitive reactance; avalanche voltage\nC\tPeak load impedance; peak voltage\nD\tPeak inverse voltage; average forward current\n> During conduction, the diode must support the average forward current. Under reverse bias, the diode must support the peak inverse voltage present across it."
}
]
},
{
"content": "output filtering",
"children": [
{
"content": "A-4-1-10 (B) In a high voltage power supply, why should a resistor and capacitor be wired in parallel with the power-supply rectifier diodes?\nA\tTo ensure that the current through each diode is about the same\nB\tTo equalize voltage drops and guard against transient voltage spikes\nC\tTo smooth the output waveform\nD\tTo decrease the output voltage\n> Parallel capacitors are used to bypass voltage spikes. Parallel resistors across each diode in a chain of diodes equalize reverse voltage."
}
]
},
{
"content": "full-wave rectifier",
"children": [
{
"content": "A-4-1-11 (D) What is the output waveform of an unfiltered full-wave rectifier connected to a resistive load?\nA\tA steady DC voltage\nB\tA sine wave at half the frequency of the AC input\nC\tA series of pulses at the same frequency as the AC input\nD\tA series of pulses at twice the frequency of the AC input\n> A full-wave rectifier puts both half-cycles to contribution: pulsating direct current with 120 zero-to-peak transitions per second is produced."
}
]
},
{
"content": "filter chokes",
"children": [
{
"content": "A-4-2-1 (C) Filter chokes are rated according to:\nA\tpower loss\nB\tbreakdown voltage\nC\tinductance and current-handling capacity\nD\treactance at 1000 Hz\n> Filter chokes are wired in series with the rectifier output. The choke must support the current drawn by the load. Its inductance influences the reduction in ripple."
}
]
},
{
"content": "input filter"
},
{
"content": "series chokes",
"children": [
{
"content": "A-4-2-7 (C) In a power supply, series chokes will:\nA\timpede the passage of DC but will pass the AC component\nB\timpede both DC and AC\nC\treadily **pass the DC** but will **impede** the flow of the **AC component**\nD\treadily pass the DC and the AC component",
"children": [
{
"content": "> Inductors oppose changes in current. Stable DC current is not affected but AC ripple is minimized."
}
]
},
{
"content": "A **bleeder resistor** provides a path for a continuous trickle of current through the choke, to ameliorate inrush current and consequent back-EMF.",
"children": [
{
"content": "A-4-2-8 (C) When using a choke input filter, a minimum current should be drawn all the time when the device is switched on. This can be accomplished by:\nA\tplacing an ammeter in the output circuit\nB\tincreasing the value of the output capacitor\nC\tincluding a suitable **bleeder resistance**\nD\tutilizing a full-wave bridge rectifier circuit",
"children": [
{
"content": "> Only the expected answer has an impact on DC current flowing through the filter whether an external load is connected or not."
}
]
}
]
}
]
},
{
"content": "input filtering",
"children": [
{
"content": "capacitor filter",
"children": [
{
"content": "A-4-2-3 (D) The advantage of the **capacitor** input filter over the choke input filter is:\nA\tbetter filtering action or smaller ripple voltage\nB\timproved voltage regulation\nC\tlower peak rectifier currents\nD\ta **higher** terminal **voltage output**",
"children": [
{
"content": "> Regulation is the change in voltage from no-load to full-load. The first filter element determines the classification. Capacitor-input filters ensure high output voltage but poor regulation: voltage soars to the peak AC value under no load and drops under load. Capacitor-input leads to high peak rectifier current. Choke-input filters limit the soar in voltage through counter-EMF and by opposing capacitor charge current. Peak rectifier current is constrained but output voltage approximates the average value of the AC waveform. Half-wave circuits have the poorest regulation."
}
]
}
]
},
{
"content": "series choke filter - opposes changes in current due to back-EMF",
"children": [
{
"content": "A-4-2-4 (B) With a normal load, the choke input filter will give the:\nA\thighest output voltage\nB\t**best regulated** output\nC\tgreatest percentage of ripple\nD\tgreatest ripple frequency",
"children": [
{
"content": "> Regulation is the change in voltage from no-load to full-load. The first filter element determines the classification. Capacitor-input filters ensure high output voltage but poor regulation: voltage soars to the peak AC value under no load and drops under load. Capacitor-input leads to high peak rectifier current. Choke-input filters limit the soar in voltage through counter-EMF and by opposing capacitor charge current. Peak rectifier current is constrained but output voltage approximates the average value of the AC waveform. Half-wave circuits have the poorest regulation."
}
]
}
]
},
{
"content": "A-4-2-5 (C) There are two types of filters in general use in a power supply. They are called:\nA\tchoke input and capacitor output\nB\tchoke output and capacitor input\nC\tchoke input and capacitor input\nD\tchoke output and capacitor output",
"children": [
{
"content": "> Regulation is the change in voltage from no-load to full-load. The first filter element determines the classification. Capacitor-input filters ensure high output voltage but poor regulation: voltage soars to the peak AC value under no load and drops under load. Capacitor-input leads to high peak rectifier current. Choke-input filters limit the soar in voltage through counter-EMF and by opposing capacitor charge current. Peak rectifier current is constrained but output voltage approximates the average value of the AC waveform. Half-wave circuits have the poorest regulation."
}
]
}
]
},
{
"content": "regulation",
"children": [
{
"content": "A-4-2-2 (D) Which of the following circuits gives the **best regulation**, under similar load conditions?\nA\tA half-wave bridge rectifier with a capacitor input filter\nB\tA half-wave rectifier with a **choke** input **filter**\nC\tA full-wave rectifier with a capacitor input filter\nD\tA full-wave rectifier with a **choke** input **filter**",
"children": [
{
"content": "> Regulation is the change in voltage from no-load to full-load. The first filter element determines the classification. Capacitor-input filters ensure high output voltage but poor regulation: voltage soars to the peak AC value under no load and drops under load. Capacitor-input leads to high peak rectifier current. Choke-input filters limit the soar in voltage through counter-EMF and by opposing capacitor charge current. Peak rectifier current is constrained but output voltage approximates the average value of the AC waveform. Half-wave circuits have the poorest regulation."
}
]
}
]
},
{
"content": "bleeder resistor",
"children": [
{
"content": "A-4-2-6 (B) The main function of the **bleeder resistor** in a power supply is to provide a discharge path for the capacitor in the power supply. But it may also be used for a secondary function, which is to:\nA\tact as a secondary smoothing device in conjunction with the filter\nB\timprove voltage regulation\nC\tprovide a ground return for the transformer\nD\tinhibit the flow of current through the supply",
"children": [
{
"content": "> Regulation is the change in voltage from no-load to full-load. By ensuring a certain minimum current draw on the supply, the bleeder prevents the capacitors from fully charging up to peak AC values when no external load is connected."
}
]
}
]
},
{
"content": "no-load",
"children": [
{
"content": "A-4-2-11 (D) In a properly designed choke input filter power supply, the no-load voltage across the filter capacitor will be about nine-tenths of the AC RMS voltage; yet it is advisable to use capacitors rated at the peak transformer voltage. Why is this large safety margin suggested?\nA\tResonance can be set up in the filter producing high voltages\nB\tUnder heavy load, high currents and voltages are produced\nC\tUnder no-load conditions, the current could reach a high level\nD\tUnder **no-load** conditions and a **burned-out bleeder**, voltages could reach the peak transformer voltage",
"children": [
{
"content": "> Inductors oppose changes in current. If no current at all is drawn from a choke-input filter, the effect of the inductor vanishes: no more counter-EMF or opposition to peak capacitor charging current. Subsequent capacitors are allowed to fully charge to peak AC values. [ nine tenths the RMS: RMS is 0.707 times peak, average is 0.637 times peak, 0.637 is nine tenths of 0.707 ]"
}
]
}
]
},
{
"content": "resonance",
"children": [
{
"content": "A-4-2-9 (C) In the design of a power supply, the designer must be careful of **resonance effects** because the ripple voltage could build up to a high value. The components that must be carefully selected are:\nA\tfirst capacitor and second capacitor\nB\tfirst choke and second capacitor\nC\tfirst **choke** and first **capacitor**\nD\tthe bleeder resistor and the first choke",
"children": [
{
"content": "> Series resonance in the first choke and first capacitor across the rectifier may cause excessive rectifier peak current and abnormally high peak reverse voltages on the diodes."
}
]
},
{
"content": "A-4-2-10 (B) Excessive rectifier peak current and abnormally high peak inverse voltages can be caused in a power supply by the filter forming a:\nA\ttuned inductance in the filter choke\nB\t**series resonant circuit** with the first choke and first capacitor\nC\tshort circuit across the bleeder\nD\tparallel resonant circuit with the first choke and second capacitor",
"children": [
{
"content": "> Series resonance in the first choke and first capacitor across the rectifier may cause excessive rectifier peak current and abnormally high peak reverse voltages on the diodes."
}
]
}
]
},
{
"content": "linear regulator",
"children": [
{
"content": "A-4-3-1 (C) What is one characteristic of a linear electronic voltage regulator?\nA\tA pass transistor switches from its \"on\" state to its \"off\" state\nB\tThe control device is switched on or off, with the duty cycle proportional to the line or load conditions\nC\tThe conduction of a control element is varied in direct proportion to the line voltage or load current\nD\tIt has a ramp voltage at its output\n> In a 'linear' voltage regulator, a voltage higher than necessary is first produced; this voltage is brought down through a voltage dropping component. A regulator circuit (e.g., a Zener in a shunt configuration) may draw more or less current through a passive resistor to compensate for external changes. The dropping element, in a series configuration, may be a tube or transistor whose conduction may be varied. In a switching regulator, the incoming DC is switched on and off; the on time is varied so that the average DC output is maintained regardless of current draw."
},
{
"content": "A-4-3-3 (C) What device is typically used as a stable reference voltage in a linear voltage regulator?\nA\tA varactor diode\nB\tA junction diode\nC\tA Zener diode\nD\tAn SCR\n> Remember your Basic Qualification? Zener diodes maintain a constant voltage across their terminals."
},
{
"content": "A-4-3-4 (C) What type of linear regulator is used in applications requiring efficient utilization of the primary power source?\nA\tA constant current source\nB\tA shunt current source\nC\tA series regulator\nD\tA shunt regulator\n> Key word: EFFICIENT. A linear regulator with an active series dropping device (tube or transistor) wastes less energy as dropping resistance is adjusted to whatever current is drawn. A linear regulator with a passive dropping resistor and a control device in a shunt configuration (Zener, tube or transistor) is wasteful because a fixed amount of current is needed to maintain a given drop in voltage regardless of load current; the device draws less when load current increases and vice-versa. The shunt configuration may be needed if the unregulated source demands a constant load."
},
{
"content": "A-4-3-5 (C) What type of linear voltage regulator is used in applications requiring a constant load on the unregulated voltage source?\nA\tA shunt current source\nB\tA series regulator\nC\tA shunt regulator\nD\tA constant current source\n> Key words: CONSTANT LOAD. A linear regulator with an active series dropping device (tube or transistor) wastes less energy as dropping resistance is adjusted to whatever current is drawn. A linear regulator with a passive dropping resistor and a control device in a shunt configuration (Zener, tube or transistor) is wasteful because a fixed amount of current is needed to maintain a given drop in voltage regardless of load current; the device draws less when load current increases and vice-versa. The shunt configuration may be needed if the unregulated source demands a constant load."
},
{
"content": "A-4-3-6 (C) How is remote sensing accomplished in a linear voltage regulator?\nA\tA load connection is made outside the feedback loop\nB\tBy wireless inductive loops\nC\tA feedback connection to an error amplifier is made directly to the load\nD\tAn error amplifier compares the input voltage to the reference voltage\n> Key word: REMOTE. Voltage regulation relies on comparing the output voltage to a set reference and using the error to adjust conduction in the control element of the regulator. Sensing the voltage at the load rather than at the output terminals of the power supply compensates for losses all the way out to the load."
}
]
},
{
"content": "switching regulator",
"children": [
{
"content": "duty cycle is proportional to load",
"children": [
{
"content": "A-4-3-2 (B) What is one characteristic of a **switching** voltage regulator?\nA\tIt gives a ramp voltage at its output\nB\tThe control device is switched on and off, with the **duty cycle proportional** to the line or **load conditions**\nC\tThe conduction of a control element is varied in direct proportion to the line voltage or load current\nD\tIt provides more than one output voltage",
"children": [
{
"content": "> In a 'linear' voltage regulator, a voltage higher than necessary is first produced; this voltage is brought down through a voltage dropping component. A regulator circuit (e.g., a Zener in a shunt configuration) may draw more or less current through a passive resistor to compensate for external changes. The dropping element, in a series configuration, may be a tube or transistor whose conduction may be varied. In a switching regulator, the incoming DC is switched on and off; the on time is varied so that the average DC output is maintained regardless of current draw."
}
]
}
]
}
]
},
{
"content": "three terminal regulator",
"children": [
{
"content": "consists of:\n* voltage reference, \n* error amplifier, \n* sensing resistors and transistors, and\n* a pass element",
"children": [
{
"content": "A-4-3-9 (A) What type of voltage regulator contains a voltage reference, error amplifier, sensing resistors and transistors, and a pass element in one package?\nA\tA **three-terminal regulator**\nB\tAn op-amp regulator\nC\tA switching regulator\nD\tA Zener regulator",
"children": [
{
"content": "> A three-terminal regulator is a single integrated circuit comprising a voltage reference, a comparator, an error amplifier, sensing resistors and a pass transistor. Some include thermal shutdown, current foldback and over-voltage protection. The three terminals are: unregulated DC input, regulated DC output and ground. Specifications include: maximum output current, maximum output voltage, maximum input voltage and minimum input voltage (because a minimum voltage differential is needed to maintain regulation, the drop-out voltage)."
}
]
},
{
"content": "A-4-3-7 (C) What is a **three-terminal regulator**?\nA\tA regulator containing three error amplifiers and sensing transistors\nB\tA regulator that supplies three voltages with variable current\nC\tA regulator containing a voltage reference, error amplifier, sensing resistors and transistors, and a pass element\nD\tA regulator that supplies three voltages at a constant current",
"children": [
{
"content": "> A three-terminal regulator is a single integrated circuit comprising a voltage reference, a comparator, an error amplifier, sensing resistors and a pass transistor. Some include thermal shutdown, current foldback and over-voltage protection. The three terminals are: unregulated DC input, regulated DC output and ground. Specifications include: maximum output current, maximum output voltage, maximum input voltage and minimum input voltage (because a minimum voltage differential is needed to maintain regulation, the drop-out voltage)."
}
]
}
]
},
{
"content": "rated by output votlage, and (maximum) output current",
"children": [
{
"content": "A-4-3-8 (B) In addition to an input voltage range what are the important characteristics of a three-terminal regulator?\nA\tOutput voltage and minimum output current\nB\t**Output voltage** and **maximum output current**\nC\tMaximum output voltage and minimum output current\nD\tMinimum output voltage and maximum output current",
"children": [
{
"content": "> A three-terminal regulator is a single integrated circuit comprising a voltage reference, a comparator, an error amplifier, sensing resistors and a pass transistor. Some include thermal shutdown, current foldback and over-voltage protection. The three terminals are: unregulated DC input, regulated DC output and ground. Specifications include: maximum output current, maximum output voltage, maximum input voltage and minimum input voltage (because a minimum voltage differential is needed to maintain regulation, the drop-out voltage)."
}
]
}
]
},
{
"content": "A-4-3-11 (A) A modern type of regulator, which features a reference, high-gain amplifier, temperature-compensated voltage sensing resistors and transistors as well as a pass element is commonly referred to as a:\nA\t**three-terminal regulator**\nB\tnine-pin terminal regulator\nC\ttwenty-four pin terminal\nD\tregulator six-terminal regulator",
"children": [
{
"content": "> A three-terminal regulator is a single integrated circuit comprising a voltage reference, a comparator, an error amplifier, sensing resistors and a pass transistor. Some include thermal shutdown, current foldback and over-voltage protection. The three terminals are: unregulated DC input, regulated DC output and ground. Specifications include: maximum output current, maximum output voltage, maximum input voltage and minimum input voltage (because a minimum voltage differential is needed to maintain regulation, the drop-out voltage)."
}
]
}
]
},
{
"content": "types of regulators",
"children": [
{
"content": "Two types of regulators:\n* linear\n* switching",
"children": [
{
"content": "A-4-3-10 (D) When extremely low ripple is required, or when the voltage supplied to the load must remain constant under conditions of large fluctuations of current and line voltage, a closed-loop amplifier is used to regulate the power supply. There are two main categories of electronic regulators. They are:\nA\tnon-linear and switching\nB\tlinear and non-linear\nC\tstiff and switching\nD\t**linear** and **switching**",
"children": [
{
"content": "> In a 'linear' voltage regulator, a voltage higher than necessary is first produced; this voltage is brought down through a voltage dropping component. A regulator circuit (e.g., a Zener in a shunt configuration) may draw more or less current through a passive resistor to compensate for external changes. The dropping element, in a series configuration, may be a tube or transistor whose conduction may be varied. In a switching regulator, the incoming DC is switched on and off; the on time is varied so that the average DC output is maintained regardless of current draw."
}
]
}
]
},
{
"content": "A-4-4-2 (D) In any regulated power supply, the output is cleanest and the regulation is best:\nA\tacross the secondary of the pass transistor\nB\tacross the load\nC\tat the output of the pass transistor\nD\tat the point where the **sampling network** or **error amplifier** is connected",
"children": [
{
"content": "> A voltage regulator maintains a stable output by comparing a sample of the output voltage with a reference and adjusting conduction in the pass transistor accordingly. The corrective action is only accurate for the precise point where the measurement is taken. Because of losses, the load itself may find itself at a lower voltage: this is the reason for 'remote sensing' in certain applications."
}
]
}
]
},
{
"content": "series-regulated",
"children": [
{
"content": "A-4-4-1 (D) In a series-regulated power supply, the power dissipation of the **pass transistor** is:\nA\tthe inverse of the load current and the input/output voltage differential\nB\tdependent upon the peak inverse voltage appearing across the Zener diode\nC\tindirectly proportional to the load voltage and the input/output voltage differential\nD\tdirectly **proportional** to the load **current** and the input/output voltage differential",
"children": [
{
"content": "> The pass transistor is the device acting as a variable resistor to drop the unregulated DC source down to the regulated output. Power is voltage times current: in this case, the difference in voltage from input to output times the current drawn by the load."
}
]
}
]
},
{
"content": "regulation",
"children": [
{
"content": "The exam distinguished between \"static\" and \"dynamic\" regulation; that is, the response to fast or slow changes in load",
"children": [
{
"content": "A-4-4-4 (A) The regulation of **long-term** changes in the load resistance of a power supply is called:\nA\t**static regulation**\nB\tactive regulation\nC\tanalog regulation\nD\tdynamic regulation",
"children": [
{
"content": "> Key words: LONG-TERM. Regulation is the change in voltage from no-load to full-load. Static regulation relates to the supply's performance in relation with long-term changes in load resistance or line variations (AC source). Dynamic regulation is required when the current draw varies as a Morse key is pressed (CW) or with each syllable (SSB) in a final amplifier. A large output capacitor, the last in the filter configuration, can improve dynamic regulation."
}
]
}
]
},
{
"content": "A-4-4-5 (A) The regulation of **short-term** changes in the load resistance of a power supply is called:\nA\tdynamic regulation\nB\tstatic regulation\nC\tanalog regulation\nD\tactive regulation",
"children": [
{
"content": "> Key words: SHORT-TERM. Regulation is the change in voltage from no-load to full-load. Static regulation relates to the supply's performance in relation with long-term changes in load resistance or line variations (AC source). Dynamic regulation is required when the current draw varies as a Morse key is pressed (CW) or with each syllable (SSB) in a final amplifier. A large output capacitor, the last in the filter configuration, can improve dynamic regulation."
}
]
},
{
"content": "A-4-4-6 (C) The **dynamic regulation** of a power supply is improved by increasing the value of:\nA\tthe input capacitor\nB\tthe bleeder resistor\nC\tthe **output capacitor**\nD\tthe choke",
"children": [
{
"content": "> Regulation is the change in voltage from no-load to full-load. Static regulation relates to the supply's performance in relation with long-term changes in load resistance or line variations (AC source). Dynamic regulation is required when the current draw varies as a Morse key is pressed (CW) or with each syllable (SSB) in a final amplifier. A large output capacitor, the last in the filter configuration, can improve dynamic regulation."
}
]
},
{
"content": "A-4-4-7 (D) The **output** capacitor, in a power supply filter used to provide power for an SSB or CW transmitter, will give better dynamic regulation if:\nA\tthe negative terminal of the electrolytic capacitor is connected to the positive and the positive terminal to ground\n~~B\ta battery is placed in series with the output capacitor~~\nC\tit is placed in series with other capacitors\nD\tthe output capacitance is **increased**",
"children": [
{
"content": "> Regulation is the change in voltage from no-load to full-load. Static regulation relates to the supply's performance in relation with long-term changes in load resistance or line variations (AC source). Dynamic regulation is required when the current draw varies as a Morse key is pressed (CW) or with each syllable (SSB) in a final amplifier. A large output capacitor, the last in the filter configuration, can improve dynamic regulation."
}
]
}
]
},
{
"content": "load resistance",
"children": [
{
"content": "The voltage and current drawn by the load can be expressed as a resistance",
"children": [
{
"content": "A-4-4-3 (A) When discussing a power supply the_______ resistance is equal to the **output voltage** divided by the **total current** drawn, including the current drawn by the bleeder resistor:\nA\tload\nB\tideal\nC\trectifier\nD\tdifferential",
"children": [
{
"content": "> Per Ohm's Law, resistance is voltage divided by current. Output voltage and total current drawn describe the load placed on the power supply."
}
]
}
]
}
]
},
{
"content": "reverse voltage protection",
"children": [
{
"content": "A-4-4-11 (A) In a regulated power supply, a **diode** connected across the input and output terminals of a regulator is used to:\nA\tprotect the regulator from **reverse voltages**\nB\tprovide an RF by-pass for the voltage control\nC\tprovide additional capacity\nD\tprotect the regulator from voltage fluctuations in the primary of the transformer",
"children": [
{
"content": "> A fast reverse-biased diode between the output and input terminals prevents a large capacitor following the three-terminal regulator from discharging through the regulator if the input was ever short-circuited."
}
]
}
]
}
]
},
{
"content": "\n{L05} Amplifiers, Mixers and Frequency Multipliers.",
"children": [
{
"content": "There are four [*classes* of amplifer](https://www.typesnuses.com/different-types-of-amplifiers/), distinguished by the conduction angle of their transistors, and efficiency. They are:\n\n* Class A (full-cycle, linear, inefficient)\n* Class B (half-cycle)\n* Class AB (compromise for SSB)\n* Class C (FM, RTTY, CW, mixer)\n\n![](https://www.typesnuses.com/wp-content/uploads/Power-Amplifiers-Summary.gif)\n\nThe performance metrics of interest are:\n* linearity,\n* distortion, and \n* efficiency. ",
"children": [
{
"content": "* [**Class A**](https://www.electronics-tutorials.ws/amplifier/amp_5.html) amplifiers operate over a full cycle and have good linearity and distortion characteristics, but are inefficient.\n![](https://www.typesnuses.com/wp-content/uploads/Class-A-Amplifier.gif)",
"children": [
{
"content": "The transistor in a Class A amplifier operates over a *full* cycle.",
"children": [
{
"content": "A-2-6-1 (A) For what portion of a signal cycle does a Class A amplifier operate?\nA\tThe entire cycle\nB\tExactly 180 degrees\nC\tMore than 180 degrees but less than 360 degrees\nD\tLess than 180 degrees",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
},
{
"content": "A-2-6-10 (C) Which class of amplifier operates over the full cycle?\nA\tClass B\nB\tClass C\nC\tClass A\nD\tClass AB",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
},
{
"content": "Consequently, they have *low distortion*.\n\nThey also have *high linearity*.",
"children": [
{
"content": "A-2-6-2 (A) Which class of amplifier has the highest linearity and least distortion?\nA\tClass A\nB\tClass AB\nC\tClass B\nD\tClass C",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
},
{
"content": "They are least efficient.",
"children": [
{
"content": "A-2-6-8 (B) Which class of amplifier provides the least efficiency?\nA\tClass AB\nB\tClass A\nC\tClass C\nD\tClass B",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
}
]
},
{
"content": "* [**Class B**](https://www.electronics-tutorials.ws/amplifier/amp_6.html) amplifiers operate for a half-cycle.\n![](https://www.typesnuses.com/wp-content/uploads/Class-B-Amplifier.gif)",
"children": [
{
"content": "Class B amplifer consists of two amplifying elements in a \"push-pull\" configuration. Each transistor conducts for a **half-cycle**.",
"children": [
{
"content": "A-2-6-4 (A) For what portion of a cycle does a Class B amplifier operate?\nA\t180 degrees\nB\tLess than 180 degrees\nC\tMore than 180 degrees but less than 360 degrees\nD\tThe entire cycle",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
}
]
},
{
"content": "* In Between Class A and Class B are [**Class AB**](https://www.electronics-tutorials.ws/amplifier/class-ab-amplifier.html) amplifiers, which operate for somewhat more than a cycle.\n![](https://www.typesnuses.com/wp-content/uploads/Class-AB-Amplifier.gif)",
"children": [
{
"content": "The transistors in a Class AB amplifiers operate for *more* than half-a-cycle, but less than a full cycle.",
"children": [
{
"content": "A-2-6-3 (D) For what portion of a cycle does a Class AB amplifier operate?\nA\tExactly 180 degrees\nB\tThe entire cycle\nC\tLess than 180 degrees\nD\tMore than 180 degrees but less than 360 degrees",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
},
{
"content": "Most-often used for ham linear power amplifiers, as the amplitude of e.g. an SSB or AM signal varies in amplitude over a wide dynamic range."
}
]
},
{
"content": "* **Class C** amplifiers operate for less than half-a-cycle, but are relatively efficient.\n\n![](https://www.typesnuses.com/wp-content/uploads/Class-C-Amplifier.gif)",
"children": [
{
"content": "**Class C** amplifiers also operate for less than half-a-cycle.",
"children": [
{
"content": "A-2-6-5 (C) For what portion of a signal cycle does a Class C amplifier operate?\nA\tThe entire cycle\nB\t180 degrees\nC\tLess than 180 degrees\nD\tMore than 180 degrees but less than 360 degrees",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
},
{
"content": "A-2-6-11 (A) Which class of amplifier operates over less than 180 degrees of the cycle?\nA\tClass C\nB\tClass AB\nC\tClass A\nD\tClass B",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
},
{
"content": "Because the resulting waveform is very much not sinusoidal, they have **high distortion** (lots of harmonics).\n\nBecause they are **non-linear** they bad for signals with a varying amplitude, and *good* for signals at a *constant* amplitude (like **CW**, **FM**, and **RTTY**.)",
"children": [
{
"content": "A-2-6-9 (A) Which class of amplifier has the poorest linearity and the most distortion?\nA\tClass C\nB\tClass AB\nC\tClass A\nD\tClass B",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
},
{
"content": "However, they have high efficiency.",
"children": [
{
"content": "A-2-6-6 (B) Which of the following classes of amplifier provides the highest efficiency?\nA\tClass B\nB\tClass C\nC\tClass A\nD\tClass AB",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
},
{
"content": "A-2-6-7 (A) Which of the following classes of amplifier would provide the highest efficiency in the output stage of a CW, RTTY or FM transmitter?\nA\tClass C\nB\tClass AB\nC\tClass B\nD\tClass A",
"children": [
{
"content": "> Class A: 360 degrees, best linearity, least distortion, poor efficiency [25 to 30%]. Class AB: significantly more than 180 but less than 360 degrees, very acceptable linearity, medium efficiency [50 to 60%]. Class B: 180 degrees, acceptable linearity, medium efficiency [up to 65%]. Class C: much less than 180 degrees, poor linearity, high distortion, best efficiency [up to 80%]. Usable with constant amplitude signals (CW,FM) where 'flywheel' effect in tank circuit maintains the waveform. Harmonic-rich output is useful in frequency multiplier."
}
]
}
]
}
]
},
{
"content": "Efficiency in this contact refers to DC power input compared to RF power output."
}
]
},
{
"content": "There are three [FET amplifier configurations](https://www.electronics-notes.com/articles/analogue_circuits/fet-field-effect-transistor/fet-circuit-configurations.php) of interest:\n* common source\n* common gate\n* common drain",
"children": [
{
"content": "In the **[common source](https://www.electronics-notes.com/articles/analogue_circuits/fet-field-effect-transistor/common-source-amplifier-circuit.php)** amplifer, the source terminal is common to input and output.\n\nThe gate is the input terminal.\n\nThe drain is the output terminal.\n\n![common source configuration](https://www.electronics-notes.com/images/transistor-fet-configuration-common-source-summary-01.svg)\n",
"children": [
{
"content": "The **gate biasing network** (R1 and R2 in the schamtic below) determines the **input impedance**.",
"children": [
{
"content": "A-2-7-1 (B) What determines the input impedance of a FET common-source amplifier?\nA\tThe input impedance is essentially determined by the resistance between the drain and substrate\nB\tThe input impedance is essentially determined by the gate biasing network\nC\tThe input impedance is essentially determined by the resistance between the source and substrate\nD\tThe input impedance is essentially determined by the resistance between the source and the drain",
"children": [
{
"content": "> The Junction FET is considered a high impedance device. Because the Gate in a Junction FET is always reversed-biased, its input impedance is very high; the input impedance of the whole circuit is determined by the external Gate bias resistor. The output impedance is determined primarily by the resistor acting as a load in the Drain circuit."
}
]
}
]
},
{
"content": "![common source schematic](https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/amplifier-amp14.gif)"
},
{
"content": "The **drain resistor** (R_D) determines the **output impedance**.",
"children": [
{
"content": "A-2-7-2 (A) What determines the output impedance of a FET common-source amplifier?\nA\tThe output impedance is essentially determined by the drain resistor\nB\tThe output impedance is essentially determined by the drain supply voltage\nC\tThe output impedance is essentially determined by the gate supply voltage\nD\tThe output impedance is essentially determined by the input impedance of the FET",
"children": [
{
"content": "> The Junction FET is considered a high impedance device. Because the Gate in a Junction FET is always reversed-biased, its input impedance is very high; the input impedance of the whole circuit is determined by the external Gate bias resistor. The output impedance is determined primarily by the resistor acting as a load in the Drain circuit."
}
]
}
]
},
{
"content": "The BJT [**common-emitter**](https://www.electronics-tutorials.ws/amplifier/amp_2.html) configuration is similar to the FET common-source configuration.",
"children": [
{
"content": "A-2-7-9 (A) The FET amplifier common source circuit is similar to which of the following bipolar transistor amplifier circuits?\nA\tCommon emitter\nB\tCommon collector\nC\tCommon base\nD\tCommon mode",
"children": [
{
"content": "> Remember your Basic Qualification? Source, Gate, Drain in the FET compare to Emitter, Base, Collector in the bipolar."
}
]
}
]
},
{
"content": "The input and output are 180 degrees out of phase.",
"children": [
{
"content": "A-2-7-6 (D) In the common emitter amplifier, when the input and output signals are compared:\nA\tthe output signal leads the input signal by 90 degrees\nB\tthe output signal lags the input signal by 90 degrees\nC\tthe signals are in phase\nD\tthe signals are 180 degrees out of phase",
"children": [
{
"content": "> Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching."
}
]
}
]
}
]
},
{
"content": "[common-base amplifier](https://www.electronics-tutorials.ws/amplifier/common-base-amplifier.html)\n\n![common-base configuration](https://www.electronics-notes.com/images/transistor-configuration-common-base-summary-01.svg)",
"children": [
{
"content": "The input and output signals are in phase.",
"children": [
{
"content": "A-2-7-4 (B) In the common base amplifier, when the input and output signals are compared:\nA\tthe signals are 180 degrees out of phase\nB\tthe signals are in phase\nC\tthe output signal lags the input signal by 90 degrees\nD\tthe output signals leads the input signal by 90 degrees",
"children": [
{
"content": "> Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching."
}
]
}
]
},
{
"content": "The input impedance is very low.\n>The common gate or grounded gate circuit configuration is used for VHF and UHF RF amplifiers where the low input impedance allows accurate matching to the feeder impedance which is typically 50Ω or 75Ω. [(Source)](view-source:https://www.electronics-notes.com/articles/analogue_circuits/fet-field-effect-transistor/common-gate-amplifier-circuit.php)",
"children": [
{
"content": "A-2-7-5 (C) In the common base amplifier, the input impedance, when compared to the output impedance is:\nA\tonly slightly lower\nB\tvery high\nC\tvery low\nD\tonly slightly higher",
"children": [
{
"content": "> Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching."
}
]
}
]
},
{
"content": "The FET equivalent is the [common gate](https://www.electronics-notes.com/articles/analogue_circuits/fet-field-effect-transistor/common-gate-amplifier-circuit.php) configuration.\n![common base configuration](https://www.electronics-notes.com/images/transistor-fet-configuration-common-gate-summary-01.svg)",
"children": [
{
"content": "A-2-7-11 (B) The FET amplifier common gate circuit is similar to which of the following bipolar transistor amplifier circuits?\nA\tCommon emitter\nB\tCommon base\nC\tCommon mode\nD\tCommon collector",
"children": [
{
"content": "> Remember your Basic Qualification? Source, Gate, Drain in the FET compare to Emitter, Base, Collector in the bipolar."
}
]
}
]
}
]
},
{
"content": "common-collector amplifier",
"children": [
{
"content": "The FET common drain and the BJT common collector amplifers are similar. ",
"children": [
{
"content": "A-2-7-10 (B) The FET amplifier common drain circuit is similar to which of the following bipolar transistor amplifier circuits?\nA\tCommon mode\nB\tCommon collector\nC\tCommon emitter\nD\tCommon base\n> Remember your Basic Qualification? Source, Gate, Drain in the FET compare to Emitter, Base, Collector in the bipolar."
}
]
},
{
"content": "The common-drain is also called a source-follower.",
"children": [
{
"content": "A-2-7-8 (C) The FET amplifier source follower circuit is another name for:\nA\tcommon mode circuit\nB\tcommon gate circuit\nC\tcommon drain circuit\nD\tcommon source circuit\n> In a source follower stage, the Source constitutes the output; the Drain, by opposition, must be tied to a common reference (a zero reference for signals): hence the expression, common drain."
}
]
},
{
"content": "The input and output are **in phase**.",
"children": [
{
"content": "A-2-7-7 (A) In the common collector amplifier, when the input and output signals are compared:\nA\tthe signals are in phase\nB\tthe output signal leads the input signal by 90 degrees\nC\tthe output signal lags the input signal by 90 degrees\nD\tthe signals are 180 degrees out of phase",
"children": [
{
"content": "> Common Emitter: low input Z, medium output Z, 180-degrees phase shift. Common Base: very low input Z, high output Z, no phase shift. Common Collector (Common Drain, Common Plate): high input Z, low output Z, no phase shift, also known as Emitter (Source, Cathode) follower, used for isolation or impedance matching."
}
]
}
]
}
]
}
]
},
{
"content": "A [**Darlington pair**](https://www.electronics-notes.com/articles/analogue_circuits/transistor/darlington-pair.php) amplifier consists of two well-behaving cascaded transistors.",
"children": [
{
"content": "![](https://www.electronics-notes.com/images/transistor-darlington-01.svg)\n\nConsequently, it has high gain, and good input and output impedance (high and low).",
"children": [
{
"content": "A-2-7-3 (C) What are the advantages of a Darlington pair audio amplifier?\nA\tMutual gain, low input impedance and low output impedance\nB\tLow output impedance, high mutual impedance and low output current\nC\tHigh gain, high input impedance and low output impedance\nD\tMutual gain, high stability and low mutual inductance",
"children": [
{
"content": "> The Darlington pair cascades two direct-coupled emitter-follower stages; Beta parameters multiply one another. The emitter follower, just like the cathode follower or the source follower features high input impedance and low output impedance. The Darlington configuration features high gain, high input impedance and low output impedance. \"High gain\" is enough to identify the correct answer."
}
]
}
]
}
]
},
{
"content": "**Frequency multipliers** make use of the harmonics produced by Class C amplifiers.\n\n`need work here`",
"children": [
{
"content": "A multiplier is simply a class C amplifier. The (low-frequency) input. The output signal is rich in harmonics, with images at multiples of the input frequency.",
"children": [
{
"content": "A-2-9-5 (A) A **frequency multiplier** circuit must be operated in:\nA\t**class C**\nB\tclass AB\nC\tclass B\nD\tclass A",
"children": [
{
"content": "> A Frequency-Multiplier stage relies on harmonics produced by a gain device operated in Class C. The output circuit is tuned to an exact multiple of the input frequency (harmonic, typically two to four times). If greater multiplication is required, a chain of stages will be used."
}
]
}
]
},
{
"content": "The output incorporates a tuned circuit.\n\nThis could be a tank circuit, with a high impedance at the frequency of interest, shunting unwanted signals away, leaving signals at the frequency of interest.",
"children": [
{
"content": "A-2-9-9 (B) In a circuit where the components are tuned to resonate at a **higher** frequency than applied, the circuit is most likely a:\nA\ta frequency divider\nB\ta **frequency multiplier**\nC\ta VHF/UHF amplifier\nD\ta linear amplifier",
"children": [
{
"content": "> A Frequency-Multiplier stage relies on harmonics produced by a gain device operated in Class C. The output circuit is tuned to an exact multiple of the input frequency (harmonic, typically two to four times). If greater multiplication is required, a chain of stages will be used."
}
]
},
{
"content": "A-2-9-6 (A) In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in **series** between VCC+ and ground. The collector of a transistor is connected to a tap on L1. The purpose of the variable capacitor is to:\nA\t**tune** L1 to the desired harmonic\nB\tby-pass RF\nC\ttune L1 to the frequency applied to the base\nD\tprovide positive feedback",
"children": [
{
"content": "> A tuned circuit is present in the output of a frequency multiplier to select the desired harmonic and reject unwanted signals."
}
]
},
{
"content": "A-2-9-7 (C) In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in series between VCC+ and ground. The collector of a transistor is connected to a tap on L1. A fixed capacitor (C3) is connected between the VCC+ side of L1 and ground. The purpose of C3 is to:\nA\tresonate with L1\nB\tby-pass any audio components\nC\tprovide an **RF ground** at the VCC connection point of L1\nD\tform a pi filter with L1 and C2",
"children": [
{
"content": "> A capacitor between the supply and ground is a **\"bypass\"** capacitor, it serves two purposes: it provides a low-impedance path to complete the AC circuit and it keeps AC signals out of the supply line (through which they could affect other stages). This being a frequency multiplier, the capacitor is an RF bypass."
}
]
},
{
"content": "A-2-9-8 (B) In a **frequency multiplier** circuit, an inductance (L1) and a variable capacitor (C2) are connected in **series** between VCC+ and ground. The collector of a transistor is connected to a tap on L1. **C2 in conjunction with L1** operate as a:\nA\tvoltage doubler\nB\t**frequency multiplier**\nC\tfrequency divider\nD\tvoltage divider",
"children": [
{
"content": "> A tuned circuit is present in the output of a frequency multiplier to select the desired harmonic and reject unwanted signals."
}
]
}
]
},
{
"content": "Input coupled to base through DC blocking capacitor.",
"children": [
{
"content": "A-2-9-4 (D) In a frequency multiplier circuit, the **input** signal is coupled to the base of a transistor through a **capacitor**. A radio frequency choke is connected between the base of the transistor and ground. The capacitor is:\nA\tpart of the input tuned circuit\nB\ta by-pass for the circuit\nC\tpart of the output tank circuit\nD\ta **DC blocking capacitor**",
"children": [
{
"content": "> A capacitor used for coupling let AC signals through but blocks DC."
}
]
},
{
"content": "A-2-9-10 (D) In a frequency multiplier circuit, an inductance (L1) and a variable capacitor (C2) are connected in series between VCC+ and ground. The collector of a transistor is connected to a tap on L1. A fixed capacitor (C3) is connected between the VCC+ side of L1 and ground. C3 is a:\nA\tDC blocking capacitor\nB\ttuning capacitor\nC\t**coupling capacitor**\nD\tRF by-pass capacitor",
"children": [
{
"content": "> A capacitor between the supply and ground is a \"bypass\" capacitor, it serves two purposes: it provides a low-impedance path to complete the AC circuit and it keeps AC signals out of the supply line (through which they could affect other stages). This being a frequency multiplier, the capacitor is an RF bypass."
}
]
}
]
}
]
},
{
"content": "**Mixers** upconvert and downconvert signals in a way that the frequencies are additive and subtractive.",
"children": [
{
"content": "Mixers combine two input signals, with the outputs consisting of both the orignal signals, and signals at the sum and difference of the input frequncies.",
"children": [
{
"content": "A-2-9-1 (C) What is the mixing process?\nA\tThe recovery of intelligence from a modulated signal\nB\tThe elimination of noise in a wideband receiver by phase comparison\nC\tThe combination of two signals to produce **sum and difference** frequencies\nD\tThe elimination of noise in a wideband receiver by phase differentiation",
"children": [
{
"content": "> A Mixer receives two inputs. They combine within the Mixer to produce two new frequencies: the sum of the inputs and the difference between the inputs. Four frequencies are present at the output: the sum, the difference and the two original frequencies. If a Mixer is driven into non-linearity by excessively strong signals, spurious responses will be produced."
}
]
},
{
"content": "A-2-9-2 (A) What are the principal frequencies that appear at the output of a mixer circuit?\nA\tThe original frequencies and the **sum and difference** frequencies\nB\t1.414 and 0.707 times the input frequencies\nC\tThe sum, difference and square root of the input frequencies\nD\tTwo and four times the original frequency",
"children": [
{
"content": "> A Mixer receives two inputs. They combine within the Mixer to produce two new frequencies: the sum of the inputs and the difference between the inputs. Four frequencies are present at the output: the sum, the difference and the two original frequencies. If a Mixer is driven into non-linearity by excessively strong signals, spurious responses will be produced."
}
]
}
]
},
{
"content": "To transform singals to frequencies that are not multiples of each other, mixers are used.\n\nFor example, 5.3 MHz input + 9 MHz IF = 14.3 MHz output",
"children": [
{
"content": "A-2-9-11 (C) What stage in a transmitter would change a 5.3-MHz input signal to 14.3 MHz?\nA\tA frequency multiplier\nB\tA beat frequency oscillator\nC\tA **mixer**\nD\tA linear translator",
"children": [
{
"content": "> The second frequency is not a multiple of the first, this excludes the multiplier. A Frequency Multiplier stage relies on harmonics produced by a gain device operated in Class C. The output circuit is tuned to an exact multiple of the input frequency (harmonic, typically two to four times). If greater multiplication is required, a chain of stages will be used."
}
]
}
]
},
{
"content": "When mixers are overdriven, **nonlinearity** and results in **spurious signals**.",
"children": [
{
"content": "A-2-9-3 (B) What occurs when an excessive amount of signal energy reaches the mixer circuit?\nA\tMixer blanking occurs\nB\t**Spurious signals** are generated\nC\tAutomatic limiting occurs\nD\tA beat frequency is generated",
"children": [
{
"content": "> A Mixer receives two inputs. They combine within the Mixer to produce two new frequencies: the sum of the inputs and the difference between the inputs. Four frequencies are present at the output: the sum, the difference and the two original frequencies. If a Mixer is driven into **non-linearity** by excessively strong signals, spurious responses will be produced."
}
]
}
]
}
]
},
{
"content": "**Op amps** are used to amplify and filter small signals. They do not exhibit loss.",
"children": [
{
"content": "An op-amp is a differential amplifier.\n\nThe inputs and outputs are **directly** coupled (as opposed to capacitive or inductive coupling, with vacuum tube amplifers).\n\nExternal components determine the amplifier characteristics, such as gain.",
"children": [
{
"content": "A-2-8-1 (C) What is an operational amplifier (op-amp)?\nA\tAn amplifier used to increase the average output of frequency modulated amateur signals to the legal limit\nB\tA program subroutine that calculates the gain of an RF amplifier\nC\tA high-gain, direct-coupled differential amplifier whose characteristics are determined by components mounted externally\nD\tA high-gain, direct-coupled audio amplifier whose characteristics are determined by internal components of the device",
"children": [
{
"content": "> An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The \"ideal\" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance."
}
]
},
{
"content": "A-2-8-11 (B) What term is most appropriate for a high gain, direct-coupled differential amplifier whose characteristics are determined by components mounted externally?\nA\tSumming amplifier\nB\tOperational amplifier\nC\tDifference amplifier\nD\tHigh gain audio amplifier",
"children": [
{
"content": "> An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The \"ideal\" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance."
}
]
}
]
},
{
"content": "The ideal characterisitcs are:\n* infinite gain\n* flat frequency response\n* infinite input impedance\n* zero output impedance\n",
"children": [
{
"content": "A-2-8-2 (D) What would be the characteristics of the ideal op-amp?\nA\tZero input impedance, zero output impedance, infinite gain, and flat frequency response\nB\tInfinite input impedance, infinite output impedance, infinite gain and flat frequency response\nC\tZero input impedance, infinite output impedance, infinite gain, and flat frequency response\nD\tInfinite input impedance, zero output impedance, infinite gain, and flat frequency response",
"children": [
{
"content": "> An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The \"ideal\" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance."
}
]
}
]
},
{
"content": "The **input** impedance is ideally very *high*, and the **output** impedance very *low*.\n\nPractically, this means that they sink very little current and do not significantly load the signal source.",
"children": [
{
"content": "A-2-8-6 (D) What is the output impedance of a theoretically ideal op-amp?\nA\tVery high\nB\tExactly 100 ohms\nC\tExactly 1000 ohms\nD\tVery low",
"children": [
{
"content": "> An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The \"ideal\" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance."
}
]
},
{
"content": "A-2-8-5 (A) What is the input impedance of a theoretically ideal op-amp?\nA\tVery high\nB\tVery low\nC\tExactly 100 ohms\nD\tExactly 1000 ohms",
"children": [
{
"content": "> An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The \"ideal\" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance."
}
]
}
]
},
{
"content": "The **gain** of an op-amp is determined by an external **feedback network**.",
"children": [
{
"content": "A-2-8-3 (C) What determines the gain of a closed-loop op-amp circuit?\nA\tThe voltage applied to the circuit\nB\tThe collector-to-base capacitance of the PNP stage\nC\tThe external feedback network\nD\tThe PNP collector load",
"children": [
{
"content": "> An Operational Amplifier is a high gain, direct-coupled differential amplifier whose characteristics are determined mainly by external components. For example, circuit gain is determined by the feedback network from output to input. The \"ideal\" Op-Amp would have infinite gain, infinite bandwidth (i.e., constant gain at any frequency), infinite input impedance and zero output impedance."
}
]
}
]
},
{
"content": "The **offset voltage** is the potential between the input terminals in a closed-loop condition.",
"children": [
{
"content": "A-2-8-4 (D) What is meant by the term op-amp offset voltage?\nA\tThe difference between the output voltage of the op-amp and the input voltage required for the next stage\nB\tThe potential between the amplifier input terminals of the op-amp in an open-loop condition\nC\tThe output voltage of the op-amp minus its input voltage\nD\tThe potential between the amplifier input terminals of the op-amp in a closed-loop condition",
"children": [
{
"content": "> \"Offset voltage is the potential between the amplifier input terminals in the closed-loop condition. Ideally, this voltage would be zero. Offset results from imbalance between the differential input transistors (ARRL Handbook)\"."
}
]
}
]
},
{
"content": "In an **inverting** configuration, the output is a half-cycle *out of phase* from the input.",
"children": [
{
"content": "A-2-8-9 (B) What is an inverting op-amp circuit?\nA\tAn operational amplifier circuit connected such that the input impedance is held to zero, while the output impedance is high\nB\tAn operational amplifier circuit connected such that the input and output signals are 180 degrees out of phase\nC\tAn operational amplifier circuit connected such that the input and output signals are in phase\nD\tAn operational amplifier circuit connected such that the input and output signals are 90 degrees out of phase",
"children": [
{
"content": "> An \"inverting\" Op-Amp circuit introduces a 180-degrees shift: when the input goes up, the output comes down and vice-versa. With the \"non-inverting\" Op-Amp circuit, the output is in phase with the input."
}
]
}
]
},
{
"content": "In a **non-inverting** configuration, the output is *in-phase* with the input.",
"children": [
{
"content": "output is in-phase with the oA-2-8-10 (D) What is a non-inverting op-amp circuit?\nA\tAn operational amplifier circuit connected such that the input and output signals are 90 degrees out of phase\nB\tAn operational amplifier circuit connected such that the input impedance is held low, and the output impedance is high\nC\tAn operational amplifier circuit connected such that the input and output signals are 180 degrees out of phase\nD\tAn operational amplifier circuit connected such that the input and output signals are in phase",
"children": [
{
"content": "> An \"inverting\" Op-Amp circuit introduces a 180-degrees shift: when the input goes up, the output comes down and vice-versa. With the \"non-inverting\" Op-Amp circuit, the output is in phase with the input."
}
]
}
]
},
{
"content": "Op-amp **filters** are used in audio circuits, because they do not introduce loss, unlike passive filters.",
"children": [
{
"content": "A-2-8-8 (D) What are the principal uses of an op-amp RC active filter in amateur circuitry?\nA\tOp-amp circuits are used as low-pass filters at the output of transmitters\nB\tOp-amp circuits are used as filters for smoothing power supply output\nC\tOp-amp circuits are used as high-pass filters to block RFI at the input of receivers\nD\tOp-amp circuits are used as audio filters for receivers",
"children": [
{
"content": "> Inductors and Capacitors are passive components; they inevitably introduce loss. Op-Amps used in filter applications can provide a controlled amount of gain. Op-Amps are commonly used in active AUDIO filter circuits; all types of responses can be implemented (low-pass, high-pass, bandpass, band-stop, a.k.a., notch)."
}
]
},
{
"content": "A-2-8-7 (D) What are the advantages of using an op-amp instead of LC elements in an audio filter?\nA\tOp-amps are more rugged and can withstand more abuse than can LC elements\nB\tOp-amps are available in more styles and types than are LC elements\nC\tOp-amps are fixed at one frequency\nD\tOp-amps exhibit gain rather than insertion loss",
"children": [
{
"content": "> Inductors and Capacitors are passive components; they inevitably introduce loss. Op-Amps used in filter applications can provide a controlled amount of gain. Op-Amps are commonly used in active AUDIO filter circuits; all types of responses can be implemented (low-pass, high-pass, bandpass, band-stop, a.k.a., notch)."
}
]
}
]
}
]
}
]
},
{
"content": "{L11} Test Equipment and measurements.",
"children": [
{
"content": "peak-to-peak & RMS\n```\nV_rms = 0.707 V_pk\n\nV_pkpk = 2 V_pk\n```",
"children": [
{
"content": "A-3-1-1 (B) What is the easiest amplitude dimension to measure by viewing a pure sine wave on an oscilloscope?\nA\tAverage voltage\nB\t**Peak-to-peak** voltage\nC\tPeak voltage\nD\tRMS voltage\n> Key word: EASIEST. Reading the peak-to-peak amplitude of a waveform is easier than attempting to precisely center the waveform to determine the peak value. RMS and Average values can only be computed from the peak value or peak-to-peak values."
},
{
"content": "A-3-1-2 (B) What is the RMS value of a 340 volt peak-to-peak pure sine wave?\nA\t300 volts\nB\t120 volts\nC\t170 volts\nD\t240 volts\n> Peak is half the peak-to-peak. RMS (or effective) is 0.707 times the peak value. 340 volts divided by 2 times 0.707 = 120 volts RMS."
},
{
"content": "A-3-1-11 (D) A sine wave of 17 volts peak is equivalent to how many volts RMS?\nA\t24 volts\nB\t34 volts\nC\t8.5 volts\nD\t12 volts\n> Peak is half the peak-to-peak. RMS (or effective) is 0.707 times the peak value. 17 volts times 0.707 = 12 volts RMS."
},
{
"content": "A-3-1-10 (D) What is the peak-to-peak voltage of a sine wave that has an RMS voltage of 120 volts?\nA\t84.8 volts\nB\t169.7 volts\nC\t204.8 volts\nD\t339.5 volts\n> Knowing that RMS is peak times 0.707, peak must be RMS divided by 0.707 . Peak-to-peak is twice the peak value. 120 volts RMS divided by 0.707 = 170 volts peak. 170 volts peak times 2 = 340 volts peak-to-peak."
},
{
"content": "A-3-1-6 (D) The effective value of a sine wave of voltage or current is:\nA\t50% of the maximum value\nB\t100% of the maximum value\nC\t63.6% of the maximum value\nD\t70.7% of the maximum value\n> Peak is half the peak-to-peak. RMS (or effective) is 0.707 times the peak value."
},
{
"content": "A-3-1-9 (D) Which AC voltage value will produce the same amount of heat as a DC voltage, when applied to the same resistance?\nA\tThe average value\nB\tThe peak value\nC\tThe peak-to-peak value\nD\tThe RMS value\n> A kettle would bring the same quantity of water to a boil within the same time whether it runs on 120 volts DC or 120 volts RMS AC."
},
{
"content": "A-3-1-5 (D) In applying Ohm's law to AC circuits, current and voltage values are:\nA\taverage values\nB\taverage values times 1.414\nC\tnone of the proposed answers\nD\tpeak values times 0.707\n> Peak is half the peak-to-peak. RMS (or effective) is 0.707 times the peak value."
},
{
"content": "A-3-1-4 (C) If the peak value of a 100 Hz sinusoidal waveform is 20 volts, the RMS value is:\nA\t7.07 volts\nB\t16.38 volts\nC\t14.14 volts\nD\t28.28 volts\n> Peak is half the peak-to-peak. RMS (or effective) is 0.707 times the peak value. 20 volts times 0.707 = 14.14 volts RMS."
},
{
"content": "A-3-1-3 (B) What is the equivalent to the RMS value of an AC voltage?\nA\tThe AC voltage found by taking the square root of the average AC value\nB\tThe AC voltage causing the same heating of a given resistor as a DC voltage of the same value\nC\tThe AC voltage found by taking the square root of the peak AC voltage\nD\tThe DC voltage causing the same heating of a given resistor as the peak AC voltage\n> A kettle would bring the same quantity of water to a boil within the same time whether it runs on 120 volts DC or 120 volts RMS AC."
}
]
},
{
"content": "peak envelope power\n\nPeak Envelope Power (PEP) is distinct from RMS power.",
"children": [
{
"content": "A-3-2-10 (C) What is the output PEP from a transmitter, if an oscilloscope measures 800 volts peak-to-peak across a 50 ohm dummy load connected to the transmitter output?\nA\t6400 watts\nB\t3200 watts\nC\t1600 watts\nD\t800 watts\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage. In this example, 800 divided by 2 = 400 volts peak ; (400 times 0.707) squared = 80 000 ; 80 000 divided by 50 = 1600 watts PEP."
},
{
"content": "A-3-2-11 (A) An oscilloscope measures 500 volts peak-to-peak across a 50 ohm dummy load connected to the transmitter output during unmodulated carrier conditions. What would an average-reading power meter indicate under the same transmitter conditions?\nA\t625 watts\nB\t427.5 watts\nC\t884 watts\nD\t442 watts\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage. In this example, 500 divided by 2 = 250 volts peak ; (250 times 0.707) squared = 31 240 ; 31 240 divided by 50 = 625 watts PEP."
},
{
"content": "A-3-2-9 (C) What is the output PEP from a transmitter, if an oscilloscope measures 400 volts peak-to-peak across a 50 ohm dummy load connected to the transmitter output?\nA\t600 watts\nB\t1000 watts\nC\t400 watts\nD\t200 watts\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage. In this example, 400 divided by 2 = 200 volts peak ; (200 times 0.707) squared = 20 000 ; 20 000 divided by 50 = 400 watts PEP."
},
{
"content": "A-3-2-8 (C) What is the output PEP of an unmodulated carrier transmitter if a wattmeter connected to the transmitter output indicates an average reading of 1060 watts?\nA\t1500 watts\nB\t530 watts\nC\t1060 watts\nD\t2120 watts\n> Key word: UNMODULATED. This is a catch. There would be no difference between output power and PEP in the absence of modulation. [ With modulation, the answer would have been different. Some wattmeters are calibrated to read peak power. ]"
},
{
"content": "A-3-2-7 (C) What is the output PEP from a transmitter if an oscilloscope measures 500 volts peak-to-peak across a 50-ohm dummy load connected to the transmitter output?\nA\t2500 watts\nB\t500 watts\nC\t625 watts\nD\t1250 watts\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage. In this example, 500 divided by 2 = 250 volts peak ; (250 times 0.707) squared = 31 240 ; 31 240 divided by 50 = 625 watts PEP."
},
{
"content": "A-3-2-6 (D) What is the output PEP from a transmitter if an oscilloscope measures 200 volts peak-to-peak across a 50-ohm dummy load connected to the transmitter output?\nA\t400 watts\nB\t1000 watts\nC\t200 watts\nD\t100 watts\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage. In this example, 200 divided by 2 = 100 volts peak ; (100 times 0.707) squared = 5000 ; 5000 divided by 50 = 100 watts PEP."
},
{
"content": "A-3-2-5 (B) How is the output Peak-Envelope Power of a transmitter calculated if an oscilloscope is used to measure the Peak-Envelope Voltage across a dummy resistive load (where PEP = Peak-Envelope Power, PEV = Peak-Envelope Voltage, Vp = peak-voltage, RL = load resistance)?\nA\tPEP = [(1.414 PEV)(1.414 PEV)] / RL\nB\tPEP = [(0.707 PEV)(0.707 PEV)] / RL\nC\tPEP = [(Vp)(Vp)] / (RL)\nD\tPEP = (Vp)(Vp)(RL)\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage."
},
{
"content": "Instantaneous power is given by\n```\n E^2\nP = ---\n R\n```",
"children": [
{
"content": "A-3-2-4 (D) The formula to be used to calculate the power output of a transmitter into a resistor load using a voltmeter is:\nA\tP = EI/R\nB\tP = EI cos 0\nC\tP = IR\nD\tP = (E exponent 2) / R\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage."
}
]
},
{
"content": "Peak envelope power is given by:\n```\n 2 2\n (0.707 * V_pk) V_rms\nPEP = -------------- = ------\n R 2\n```",
"children": [
{
"content": "A-3-2-3 (B) Peak-Envelope Power (PEP) for SSB transmission is:\nA\ta hypothetical measurement\nB\t**Peak-Envelope Voltage (PEV) multiplied by 0.707, squared and divided by the load resistance**\nC\tpeak-voltage multiplied by peak current\nD\tequal to the RMS power\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage."
}
]
},
{
"content": "A-3-2-2 (B) To compute one of the following, multiply the peak-envelope voltage by 0.707 to obtain the RMS value, square the result and divide by the load resistance. Which is the correct answer?\nA\tpower factor\nB\t**PEP**\nC\tPIV\nD\tERP",
"children": [
{
"content": "> PIV = Peak Inverse Voltage (diode rating). ERP = Effective Radiated Power (transmit power minus line losses plus antenna gain). Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage."
}
]
},
{
"content": "A-3-2-1 (D) The power supplied to the antenna transmission line by a transmitter during an RF cycle at the highest crest of the modulation envelope is known as:\nA\tmean power\nB\tcarrier power\nC\tfull power\nD\tpeak-envelope power\n> Peak Envelope Power (PEP) in SSB is defined as the power during one cycle on a modulation peak. Knowing that P = E squared divided by R, that peak voltage is half the peak-to-peak value and that RMS voltage is peak times 0.707 . PEP can be computed as ((peak voltage times 0.707) squared ) divided by R. When given peak-to-peak, first divide by 2 to obtain peak voltage."
}
]
},
{
"content": "A (grid) **dip meter** is a tunable oscillator with a feedback current meter. ",
"children": [
{
"content": "They work best for parallel tuned circuits. The are fixed amplutuidwe with no moduilation. Interactio between the (tu ned) oscillator and the (resonant) circuit under test. Frequency must be checked with an external receiver or coutner. Only tells you presence or absence of resonance; no other quantities."
},
{
"content": "A-3-3-5 (D) A dip meter may not be used directly to:\nA\talign transmitter-tuned circuits\nB\tdetermine the frequency of oscillations\nC\talign receiver-tuned circuits\nD\tmeasure the value of capacitance or inductance\n> Key word: DIRECTLY. A 'Dip Meter' cannot measure inductance or capacitance DIRECTLY but if an unknown component is first attached to a known inductance or capacitance, the unknown value can be computed once the resonant frequency of the combination is obtained. The oscillator in a dip meter can usually be disabled to turn the instrument into an absorption wavemeter."
},
{
"content": "A-3-3-4 (B) A dip meter supplies the radio frequency energy which enables you to check:\nA\tthe adjustment of an inductor\nB\tthe resonant frequency of a circuit\nC\tthe calibration of an absorption-type wavemeter\nD\tthe impedance mismatch in a circuit",
"children": [
{
"content": "> A 'Dip Meter' is an instrument incorporating a Variable Frequency Oscillator whose resonant circuit can be placed near circuits to be tested. The oscillator's activity is monitored with a built-in meter. When the external circuit's resonant frequency matches the oscillator's frequency, energy is absorbed and a dip is observed on the meter. It works best on parallel-tuned circuits. It can be used to test antenna traps and tuned circuits in static conditions (i.e., not operating). Overcoupling, hand capacity and stray capacity all introduce errors."
}
]
},
{
"content": "A-3-3-3 (C) What two ways could a dip meter be used in an amateur station?\nA\tTo measure antenna resonance and percentage modulation\nB\tTo measure resonant frequency of antenna traps and percentage modulation\nC\tTo measure resonant frequencies of antenna **traps** and to measure a **tuned circuit** resonant frequency\nD\tTo measure antenna resonance and impedance",
"children": [
{
"content": "> A 'Dip Meter' is an instrument incorporating a Variable Frequency Oscillator whose resonant circuit can be placed near circuits to be tested. The oscillator's activity is monitored with a built-in meter. When the external circuit's resonant frequency matches the oscillator's frequency, energy is absorbed and a dip is observed on the meter. It works best on parallel-tuned circuits. It can be used to test antenna traps and tuned circuits in static conditions (i.e., not operating). Overcoupling, hand capacity and stray capacity all introduce errors."
}
]
},
{
"content": "A-3-3-2 (A) What does a dip meter do?\nA\tIt gives an **indication of the resonant frequency** of a circuit\nB\tIt measures transmitter output power accurately\nC\tIt measures field strength accurately\nD\tIt measures frequency accurately",
"children": [
{
"content": "> A 'Dip Meter' is an instrument incorporating a Variable Frequency Oscillator whose resonant circuit can be placed near circuits to be tested. The oscillator's activity is monitored with a built-in meter. When the external circuit's resonant frequency matches the oscillator's frequency, energy is absorbed and a dip is observed on the meter. It works best on parallel-tuned circuits. It can be used to test antenna traps and tuned circuits in static conditions (i.e., not operating). Overcoupling, hand capacity and stray capacity all introduce errors."
}
]
},
{
"content": "A-3-3-1 (C) What is a dip meter?\nA\tA marker generator\nB\tA field-strength meter\nC\tA variable frequency **oscillator** with metered feedback current\nD\tAn SWR meter",
"children": [
{
"content": "> A 'Dip Meter' is an instrument incorporating a Variable Frequency Oscillator whose resonant circuit can be placed near circuits to be tested. The oscillator's activity is monitored with a built-in meter. When the external circuit's resonant frequency matches the oscillator's frequency, energy is absorbed and a dip is observed on the meter. It works best on parallel-tuned circuits. It can be used to test antenna traps and tuned circuits in static conditions (i.e., not operating). Overcoupling, hand capacity and stray capacity all introduce errors."
}
]
},
{
"content": "A-3-3-8 (C) A dip meter:\nA\tmay be used only with series tuned circuits\nB\taccurately measures frequencies\nC\tshould be loosely coupled to the circuit under test\nD\tshould be tightly coupled to the circuit under test\n> A 'Dip Meter' is an instrument incorporating a Variable Frequency Oscillator whose resonant circuit can be placed near circuits to be tested. The oscillator's activity is monitored with a built-in meter. When the external circuit's resonant frequency matches the oscillator's frequency, energy is absorbed and a dip is observed on the meter. It works best on parallel-tuned circuits. It can be used to test antenna traps and tuned circuits in static conditions (i.e., not operating). Overcoupling, hand capacity and stray capacity all introduce errors."
},
{
"content": "A-3-3-11 (B) Which of the following is not a factor affecting the frequency accuracy of a dip meter?\nA\tOver coupling\nB\tTransmitter power output\nC\tHand capacity\nD\tStray capacity\n> A 'Dip Meter' is an instrument incorporating a Variable Frequency Oscillator whose resonant circuit can be placed near circuits to be tested. The oscillator's activity is monitored with a built-in meter. When the external circuit's resonant frequency matches the oscillator's frequency, energy is absorbed and a dip is observed on the meter. It works best on parallel-tuned circuits. It can be used to test antenna traps and tuned circuits in static conditions (i.e., not operating). Overcoupling, hand capacity and stray capacity all introduce errors."
}
]
},
{
"content": "AC voltmeter",
"children": [
{
"content": "A-3-1-8 (B) An AC voltmeter is calibrated to read the:\nA\tpeak value\nB\teffective value\nC\tpeak-to-peak value\nD\taverage value\n> Voltmeters normally read the RMS (or effective) value; i.e., 0.707 times the peak value."
},
{
"content": "A-3-1-7 (D) AC voltmeter scales are usually calibrated to read:\nA\tpeak voltage\nB\tinstantaneous voltage\nC\taverage voltage\nD\tRMS voltage\n> Voltmeters normally read the RMS (or effective) value; i.e., 0.707 times the peak value."
}
]
},
{
"content": "Signal generator",
"children": [
{
"content": "A-3-3-7 (C) What is a signal generator?\nA\tA low-stability oscillator used to inject a signal into a circuit under test\nB\tA high-stability oscillator which generates reference signals at exact frequency intervals\nC\tA high-stability oscillator which can produce a wide range of frequencies and amplitudes\nD\tA low-stability oscillator which sweeps through a range of frequencies\n> A 'Signal Generator' is an instrument capable of producing any of a wide range of frequencies (RF frequencies for radio work). Signal generators sometimes include a calibrated output attenuator so a given amplitude can be produced (e.g., a certain number of microvolts). Calibration in that case is only accurate if the generator feeds a circuit with the expected impedance. An instrument which \"generates reference signals at exact frequency intervals\" is a marker generator or crystal calibrator."
},
{
"content": "A-3-3-6 (B) The dial calibration on the output attenuator of a signal generator:\nA\treads half the true output when the attenuator is properly terminated\nB\treads accurately only when the attenuator is properly terminated\nC\talways reads the true output of the signal generator\nD\treads twice the true output when the attenuator is properly terminated\n> A 'Signal Generator' is an instrument capable of producing any of a wide range of frequencies (RF frequencies for radio work). Signal generators sometimes include a calibrated output attenuator so a given amplitude can be produced (e.g., a certain number of microvolts). Calibration in that case is only accurate if the generator feeds a circuit with the expected impedance. An instrument which \"generates reference signals at exact frequency intervals\" is a marker generator or crystal calibrator."
},
{
"content": "A-3-3-10 (C) The dip meter is most directly applicable to:\nA\tdigital logic circuits\nB\tseries tuned circuits\nC\tparallel tuned circuits\nD\toperational amplifier circuits\n> A 'Dip Meter' is an instrument incorporating a Variable Frequency Oscillator whose resonant circuit can be placed near circuits to be tested. The oscillator's activity is monitored with a built-in meter. When the external circuit's resonant frequency matches the oscillator's frequency, energy is absorbed and a dip is observed on the meter. It works best on parallel-tuned circuits. It can be used to test antenna traps and tuned circuits in static conditions (i.e., not operating). Overcoupling, hand capacity and stray capacity all introduce errors."
}
]
},
{
"content": "SINAD is a measurement applicable to FM receivers.",
"children": [
{
"content": "A-3-3-9 (C) Which two instruments are needed to measure FM receiver sensitivity for a 12 dB SINAD ratio (signal + noise + distortion over noise + distortion)?\nA\tOscilloscope and spectrum analyzer\nB\tReceiver noise bridge and total harmonic distortion analyser\nC\tCalibrated RF **signal generator** with FM tone modulation and **total harmonic distortion** (THD) analyzer\nD\tRF signal generator with FM tone modulation and a deviation meter",
"children": [
{
"content": "> The SINAD (signal + noise + distortion over noise + distortion) ratio takes the SNR (signal + noise over noise ratio) one step further by including distortion. A 12 dB SINAD ratio ensures that speech remains intelligible. Sensitivity expressed in those terms is the lowest RF level that will produce a usable message. The RF signal generator must be calibrated so the number of microvolts is precisely determined. Total Harmonic Distortion compares unwanted harmonic components added to the desired fundamental frequency, an audio tone in this instance."
}
]
},
{
"content": "```\nSINAD = Signal + Noise + Distortion\n ---------------------------\n Noise + Distortion\n```\nMicrovolts for 12 dB quieting",
"children": [
{
"content": "A-6-3-5 (C) How is receiver sensitivity often expressed for UHF FM receivers?\nA\tNoise Figure in decibels\nB\tOverall gain in decibels\nC\tRF level for 12 dB SINAD\nD\tRF level for a given Bit Error Rate (BER)",
"children": [
{
"content": "> The SINAD (signal + noise + distortion over noise + distortion) ratio takes the SNR (signal + noise over noise ratio) one step further by including distortion. A 12 dB SINAD ratio ensures that speech remains intelligible. Sensitivity expressed in those terms is the lowest RF level that will produce a usable message. The RF signal generator must be calibrated so the number of microvolts is precisely determined. Total Harmonic Distortion compares unwanted harmonic components added to the desired fundamental frequency, an audio tone in this instance."
}
]
}
]
}
]
},
{
"content": "Frequency counter",
"children": [
{
"content": "A-3-4-1 (C) What does a frequency counter do?\nA\tIt generates broad-band white noise for calibration\nB\tIt produces a reference frequency\nC\tIt makes frequency measurements\nD\tIt measures frequency deviation\n> Two methods exist for determining frequency: counting the number of cycles in a fixed time interval or counting the time interval for some integer number of input cycles. In both cases, the instrument relies on an internal time base ( a crystal reference oscillator ). The accuracy of the measurement depends on the accuracy and stability (short and long-term) of the time base. Speed limitations in the logic circuitry limit the frequency range for a given instrument."
},
{
"content": "A-3-4-2 (A) What factors limit the accuracy, frequency response and stability of a frequency counter?\nA\tTime base accuracy, speed of the logic, and time base stability\nB\tTime base accuracy, temperature coefficient of the logic and time base stability\nC\tNumber of digits in the readout, speed of the logic, and time base stability\nD\tNumber of digits in the readout, external frequency reference and temperature coefficient of the logic\n> Two methods exist for determining frequency: counting the number of cycles in a fixed time interval or counting the time interval for some integer number of input cycles. In both cases, the instrument relies on an internal time base ( a crystal reference oscillator ). The accuracy of the measurement depends on the accuracy and stability (short and long-term) of the time base. Speed limitations in the logic circuitry limit the frequency range for a given instrument."
},
{
"content": "A-3-4-3 (C) How can the accuracy of a frequency counter be improved?\nA\tBy using faster digital logic\nB\tBy improving the accuracy of the frequency response\nC\tBy increasing the accuracy of the time base\nD\tBy using slower digital logic\n> Two methods exist for determining frequency: counting the number of cycles in a fixed time interval or counting the time interval for some integer number of input cycles. In both cases, the instrument relies on an internal time base ( a crystal reference oscillator ). The accuracy of the measurement depends on the accuracy and stability (short and long-term) of the time base. Speed limitations in the logic circuitry limit the frequency range for a given instrument."
},
{
"content": "A-3-4-4 (D) If a frequency counter with a time base accuracy of +/- 0.1 PPM (parts per million) reads 146 520 000 Hz, what is the most that the actual frequency being measured could differ from that reading?\nA\t0.1 MHz\nB\t1.4652 Hz\nC\t1.4652 kHz\nD\t14.652 Hz\n> The reading can be off by as much as the time base accuracy in Parts Per Million times the measured frequency in megahertz: 1 part per million is one hertz per megahertz. [ In reality, an added error of plus or minus 1 count exists as the last digit displayed may have been rounded up or down. ]"
},
{
"content": "A-3-4-5 (B) If a frequency counter, with a time base accuracy of 10 PPM (parts per million) reads 146 520 000 Hz, what is the most the actual frequency being measured could differ from that reading?\nA\t1465.2 kHz\nB\t1465.2 Hz\nC\t146.52 Hz\nD\t146.52 kHz\n> The reading can be off by as much as the time base accuracy in Parts Per Million times the measured frequency in megahertz: 1 part per million is one hertz per megahertz. [ In reality, an added error of plus or minus 1 count exists as the last digit displayed may have been rounded up or down. ]"
},
{
"content": "A-3-4-6 (A) The clock in a frequency counter normally uses a:\nA\tcrystal oscillator\nB\tself-oscillating Hartley oscillator\nC\tmechanical tuning fork\nD\tfree-running multivibrator\n> Two methods exist for determining frequency: counting the number of cycles in a fixed time interval or counting the time interval for some integer number of input cycles. In both cases, the instrument relies on an internal time base ( a crystal reference oscillator ). The accuracy of the measurement depends on the accuracy and stability (short and long-term) of the time base. Speed limitations in the logic circuitry limit the frequency range for a given instrument."
},
{
"content": "A-3-4-7 (D) The frequency accuracy of a frequency counter is determined by:\nA\tthe size of the frequency counter\nB\ttype of display used in the counter\nC\tthe number of digits displayed\nD\tthe characteristics of the internal time-base generator\n> Two methods exist for determining frequency: counting the number of cycles in a fixed time interval or counting the time interval for some integer number of input cycles. In both cases, the instrument relies on an internal time base ( a crystal reference oscillator ). The accuracy of the measurement depends on the accuracy and stability (short and long-term) of the time base. Speed limitations in the logic circuitry limit the frequency range for a given instrument."
}
]
},
{
"content": "A **marker generator** produces a harmonic series of signals used to calibrate receiver dials.",
"children": [
{
"content": "A-3-4-8 (D) Which device relies on a stable low-frequency oscillator, with harmonic output, to facilitate the frequency calibration of receiver dial settings?\nA\tSignal generator\nB\tHarmonic calibrator\nC\tFrequency counter\nD\t**Frequency-marker generator**\n> A frequency marker generator (or crystal calibrator) is a relatively stable and precise oscillator rich in harmonics. It is typically used to calibrate analog station receivers by providing reference signals at known intervals on the dial. For an HF receiver, harmonics may be generated every 25, 50 or 100 kHz throughout the HF spectrum. For microwave work, harmonics of 144 MHz are useful for 432 MHz (3x), 1296 (9x), 2304 (16x), 3456 (24x), 5760 (40x), 10368 (72x) and 24192 MHz (168x). The \"harmonic calibrator\" is a bogus answer."
}
]
},
{
"content": "Zero-beat",
"children": [
{
"content": "A-3-4-9 (D) What is the traditional way of verifying the accuracy of a crystal calibrator?\nA\tCompare the oscillator with your transmitter\nB\tUse a dip-meter to determine the oscillator's fundamental frequency\nC\tCompare the oscillator with your receiver\nD\tZero-beat the crystal oscillator against a standard frequency station such as WWV\n> One way to calibrate a crystal calibrator (frequency marker generator) is to turn it on so it is heard while receiving a standard frequency station on shortwave. \"Zero beating\", which can be done audibly, is bringing, through adjustment, the difference between two frequencies down to zero. When two RF signals (calibrator and reference station) are nearly at the same frequency, they produce a heterodyne (beat) which falls in the audio range; the lower the beat note, the closer the match."
},
{
"content": "A-3-4-11 (D) You want to calibrate your station frequency reference to the WWV signal on your receiver. The resulting **beat tone** must be:\nA\ta combined frequency above both\nB\tthe mathematical mean of both frequencies\nC\tat the highest audio frequency possible\nD\tof a frequency as **low** as possible and with a period as **long** as possible",
"children": [
{
"content": "> One way to calibrate a crystal calibrator (frequency marker generator) is to turn it on so it is heard while receiving a standard frequency station on shortwave. \"Zero beating\", which can be done audibly, is bringing, through adjustment, the difference between two frequencies down to zero. When two RF signals (calibrator and reference station) are nearly at the same frequency, they produce a heterodyne (beat) which falls in the audio range; the lower the beat note, the closer the match. [ Station WWV broadcasts time and frequency information from Fort Collins, Colorado; it is maintained by the Physical Measurement Laboratory (PML) of the National Institute of Standards and Technology (NIST). ]"
}
]
}
]
},
{
"content": "VXCO",
"children": [
{
"content": "A-3-4-10 (C) Out of the following oscillators, one is NOT, by itself, considered a high-stability reference:\nA\toven-controlled crystal oscillator (OCXO)\nB\tGPS disciplined oscillator (GPSDO)\nC\tvoltage-controlled crystal oscillator (VCXO)\nD\ttemperature compensated crystal oscillator (TCXO)\n> Key word: NOT. The voltage-controlled crystal oscillator (VCXO) is always part of a larger ensemble, its stability is not controlled, but can be controlled by an external circuit. The temperature compensated crystal oscillator (TCXO) relies on a temperature sensor and some circuitry (analog or digital) to correct (compensate) the frequency. The oven-controlled crystal oscillator (OCXO) maintains the crystal at a precise and constant temperature well above ambient temperature. The GPS disciplined oscillator (GPSDO) uses a GPS (Global Positioning System) receiver to synchronize an oscillator with the highly accurate reference signals from the satellites."
}
]
},
{
"content": "Lissajous figures",
"children": [
{
"content": "Used to determine the harmonic relationship between signals at different frequencies."
},
{
"content": "```\n 100 : 150\n 2 : 3\n```",
"children": [
{
"content": "A-3-5-1 (A) If a 100 Hz signal is fed to the horizontal input of an oscilloscope and a 150 Hz signal is fed to the vertical input, what type of pattern should be displayed on the screen?\nA\tA looping pattern with **3** horizontal loops, and **2** vertical loops\nB\tA rectangular pattern 100 mm wide and 150 mm high\nC\tAn oval pattern 100 mm wide and 150 mm high\nD\tA looping pattern with 100 horizontal loops and 150 vertical loops",
"children": [
{
"content": "> Using the horizontal and vertical inputs on an oscilloscope, it is possible to compare the frequency of two sine waves or the phase relationship of two signals of equal frequency. The resulting pattern is called a \"Lissajous Figure\". Apply a known signal to the horizontal input. The ratio of the number of loops on the horizontal edge to the number on the vertical edge equals the ratio of the vertical frequency Y divided by horizontal frequency X: the number of cycles the Y frequency covers during one horizontal cycle. [French mathematician Jules-Antoine Lissajous]"
}
]
}
]
},
{
"content": "```\n 5 : 2\n100 kHz : 40 kHz\n```",
"children": [
{
"content": "A-3-5-8 (D) A 100-kHz signal is applied to the horizontal channel of an oscilloscope. A signal of unknown frequency is applied to the vertical channel. The resultant wave form has 5 loops displayed vertically and 2 loops horizontally. The unknown frequency is:\nA\t20 kHz\nB\t50 kHz\nC\t30 kHz\nD\t**40 kHz**",
"children": [
{
"content": "> Using the horizontal and vertical inputs on an oscilloscope, it is possible to compare the frequency of two sine waves or the phase relationship of two signals of equal frequency. The resulting pattern is called a \"Lissajous Figure\". Apply a known signal to the horizontal input. The ratio of the number of loops on the horizontal edge to the number on the vertical edge equals the ratio of the vertical frequency Y divided by horizontal frequency X: the number of cycles the Y frequency covers during one horizontal cycle. In this example, the unknown frequency is two fifths the known frequency. [French mathematician Jules-Antoine Lissajous]"
}
]
}
]
},
{
"content": "Also used to determine the phase relationship between signals of the same frequency.\n\nSignals that are in-phase display as a diagonal line, and approach a circle as the move out of phase.",
"children": [
{
"content": "A-3-5-7 (A) When using Lissajous figures to determine phase differences, an indication of **zero or 180 degrees** is represented on the screen of an oscilloscope by:\nA\ta **diagonal straight line**\nB\ta horizontal straight line\nC\tan ellipse\nD\ta circle",
"children": [
{
"content": "> Two in-phase signals of the same frequency applied to the X and Y amplifiers will grow exactly at the same rate: equal deflection on the X and Y create a trace at a 45 degree angle. Ponder these X and Y values: 1 and 1, 2 and 2, 3 and 3, etc. A precise 180 degree phase difference has a similar effect except the trace appears in the other two quadrants. Ponder these X and Y values: 1 and -1, 2 and -2, 3 and -3, etc. [other angles correspond to the sine function of the ratio of Y as the ellipse crosses the vertical centre axis to the maximum Y value.]"
}
]
}
]
}
]
},
{
"content": "oscilloscopes",
"children": [
{
"content": "Time-base accuracy and amplifier bandwidth determine scope performance.",
"children": [
{
"content": "A-3-5-2 (B) What factors limit the accuracy, frequency response and stability of an oscilloscope?\nA\tTube face voltage increments and deflection amplifier voltages\nB\tAccuracy of the **time base** and the **linearity** and **bandwidth** of the deflection amplifiers\nC\tDeflection amplifier output impedance and tube face frequency increments\nD\tAccuracy and linearity of the time base and tube face voltage increments",
"children": [
{
"content": "> Similarly to the frequency counter, the accuracy and stability of the time base responsible for sweeping on the horizontal axis are paramount. The top frequency is limited by the highest horizontal sweep rate and bandwidth of the horizontal and vertical deflection amplifiers."
}
]
}
]
},
{
"content": "Frequency response (range) can be increased by using a faster timebase, and increasing the deflection amplifier ",
"children": [
{
"content": "A-3-5-3 (B) How can the frequency response of an oscilloscope be improved?\nA\tBy using triggered sweep and a crystal oscillator for the timebase\nB\tBy increasing the horizontal **sweep rate** and the **vertical amplifier frequency response**\nC\tBy using a crystal oscillator as the time base and increasing the vertical sweep rate\nD\tBy increasing the vertical sweep rate and the horizontal amplifier frequency response",
"children": [
{
"content": "> Similarly to the frequency counter, the accuracy and stability of the time base responsible for sweeping on the horizontal axis are paramount. The top frequency is limited by the highest horizontal sweep rate and bandwidth of the horizontal and vertical deflection amplifiers."
}
]
}
]
},
{
"content": "Dual trace is a thing",
"children": [
{
"content": "A-3-5-4 (D) You can use an oscilloscope to display the input and output of a circuit at the same time by:\nA\tmeasuring the input on the X axis and the output on the Y axis\nB\tmeasuring the input on the X axis and the output on the Z axis\nC\tmeasuring the input on the Y axis and the output on the X axis\nD\tutilizing a **dual trace oscilloscope**",
"children": [
{
"content": "> A dual-trace oscilloscope has two distinct vertical channels. They can be used to take simultaneous measurements at different points in a circuit."
}
]
}
]
},
{
"content": "Not good for measuring FM deviation.",
"children": [
{
"content": "A-3-5-5 (C) An oscilloscope cannot be used to:\nA\tmeasure DC voltage\nB\tdetermine the amplitude of complex voltage wave forms\nC\tdetermine **FM** carrier **deviation** directly\nD\tmeasure frequency",
"children": [
{
"content": "> Measuring frequency is a matter of using the horizontal sweep rate and number of divisions to determine the period of one cycle of the waveform. Measuring deviation requires a deviation meter."
}
]
}
]
},
{
"content": "Scope \"bandwidth\" is the highest frequency it can display.",
"children": [
{
"content": "A-3-5-6 (B) The bandwidth of an oscilloscope is:\nA\ta function of the time-base accuracy\nB\tthe **highest frequency** signal the scope can display\nC\tdirectly related to gain compression\nD\tindirectly related to screen persistence",
"children": [
{
"content": "> Similarly to the frequency counter, the accuracy and stability of the time base responsible for sweeping on the horizontal axis are paramount. The top frequency is limited by the highest horizontal sweep rate and bandwidth of the horizontal and vertical deflection amplifiers."
}
]
}
]
},
{
"content": "A-3-5-9 (A) An oscilloscope probe must be compensated:\nA\tevery time the probe is used with a different oscilloscope\nB\twhen measuring a sine wave\nC\tthrough the addition of a high-value series resistor\nD\twhen measuring a signal whose frequency varies",
"children": [
{
"content": "> \"Probe compensation is the process of adjusting the probe's RC network divider so that the probe maintains its attenuation ratio over the probe's rated bandwidth. Most scopes have a square wave reference signal available on the front panel to use for compensating the probe. You can attach the probe tip to the probe compensation terminal and connect the probe to an input of the scope. Viewing the square wave reference signal, make the proper adjustments on the probe using a small screw driver so that the square waves on the scope screen look square\" (Jae-yong Chang, Agilent Technologies). Given that the input circuitry cannot be identical between instruments, adjustment must be made every time a high-impedance probe is used with a different scope."
}
]
},
{
"content": "Best way to check CW & sideband signals, by displaying waveform.",
"children": [
{
"content": "A-3-5-10 (C) What is the best instrument to use to check the signal quality of a CW or single-sideband phone transmitter?\nA\tA signal tracer and an audio amplifier\nB\tA field-strength meter\nC\tAn **oscilloscope**\nD\tA sidetone monitor",
"children": [
{
"content": "> An oscilloscope of sufficient bandwidth permits visualizing the transmitter's output. The sidetone monitor merely produces a tone when a CW transmitter is keyed. The field-strength meter reports relative field strength in proximity to antennas. The signal tracer permits troubleshooting audio circuitry."
}
]
}
]
},
{
"content": "Transmitter output checked using a sampler",
"children": [
{
"content": "A-3-5-11 (C) What is the best signal source to connect to the vertical input of an oscilloscope for checking the quality of a transmitted signal?\nA\tThe IF output of a monitoring receiver\nB\tThe audio input of the transmitter\nC\tThe **RF output** of the transmitter through a **sampling** device\nD\tThe RF signals of a nearby receiving antenna",
"children": [
{
"content": "> The most accurate representation of a transmitted signal can be viewed at the RF output of a transmitter. The correct method supposes the use of a \"sampler\" in the transmission line. That way, proper impedance match is maintained, instruments are protected from large voltages and extraneous signals are minimized."
}
]
}
]
}
]
},
{
"content": "Voltmeters & Ammeters",
"children": [
{
"content": "Meters are based on a d'Arsonval movement. A moving coil is in series with two fixed coils on either side. Passing a current through all the coils, the fields tend to align - deflecting the moving coil."
},
{
"content": "The **sensitivity** of an ammeter is the amount of current that causes full-scale deflection.",
"children": [
{
"content": "A-3-6-4 (A) The sensitivity of an ammeter is an expression of:\nA\tthe amount of current causing **full-scale deflection**\nB\tthe resistance of the meter\nC\tthe loading effect the meter will have on a circuit\nD\tthe value of the shunt resistor",
"children": [
{
"content": "> Ammeter sensitivity is the current needed for a full-scale deflection."
}
]
}
]
},
{
"content": "To decrease the sensitivity (increase the range), shunt resistors in parallel with the meter's internal resistance are used.\n\nAmmeters have a low overall resistance to reduce the impact on the circuit under test.",
"children": [
{
"content": "A-3-6-7 (D) The range of a DC ammeter can easily be extended by:\nA\tconnecting an external resistance in series with the internal resistance\nB\tchanging the internal inductance of the meter\nC\tchanging the internal capacitance of the meter to resonance\nD\tconnecting an external resistance in **parallel** with the internal resistance",
"children": [
{
"content": "> Extending the range of an ammeter supposes placing a shunt resistor across the meter movement to divert part of the current: the shunt resistor = internal resistance divided by the multiplication factor from which we will first have deducted a quantity of one."
}
]
},
{
"content": "A-3-6-1 (B) A meter has a full-scale deflection of 40 microamperes and an internal resistance of 96 ohms. You want it to read 0 to 1 mA. The value of the shunt to be used is:\nA\t40 ohms\nB\t4 ohms\nC\t24 ohms\nD\t16 ohms",
"children": [
{
"content": "> Extending the range of an ammeter supposes placing a shunt resistor across the meter movement to divert part of the current: the shunt resistor = internal resistance divided by the multiplication factor from which we will first have deducted a quantity of one. For example, making a 40 microamperes movement, with a 96 ohms internal resistance, read 1000 microamperes at full scale is a factor of 25: the shunt = 96 ohms divided by 24 (i.e., 25 minus 1) = 4 ohms. Method B: you could have computed voltage across the meter as 40 times 96 = 3840 microvolts ; and then, computed the shunt resistor as 3840 microvolts divided by 960 microamperes = 4 ohms."
}
]
},
{
"content": "A-3-6-9 (B) How can the range of an ammeter be increased?\nA\tBy adding resistance in series with the meter\nB\tBy adding resistance in parallel with the meter\nC\tBy adding resistance in series with the circuit under test\nD\tBy adding resistance in parallel with the circuit under test",
"children": [
{
"content": "> Extending the range of an ammeter supposes placing a shunt resistor across the meter movement to divert part of the current: the shunt resistor = internal resistance divided by the multiplication factor from which we will first have deducted a quantity of one."
}
]
}
]
},
{
"content": "The sensitivity of voltmeters are expressed in ohms per volt, where the resistance refers to .",
"children": [
{
"content": "A-3-6-5 (A) Voltmeter sensitivity is usually expressed in ohms per volt. This means that a voltmeter with a **sensitivity** of 20 kilohms per volt would be a:\nA\t50 microampere meter\nB\t1 milliampere meter\nC\t50 milliampere meter\nD\t100 milliampere meter",
"children": [
{
"content": "> Voltmeter sensitivity in ohms per volt: i.e., the full-scale reading times the sensitivity yields total instrument resistance. Given **sensitivity**, the current needed for full-scale voltmeter reading follows Ohm's Law: e.g., a voltmeter with a sensitivity of 20 000 ohms per volt uses a 50 microampere movement ( I = 1 volt divided by 20 000 = 50 microamperes )."
}
]
},
{
"content": "A-3-6-6 (B) The sensitivity of a voltmeter, whose **resistance** is 150 000 ohms on the 150-volt range, is:\nA\t150 ohms per volt\nB\t1000 ohms per volt\nC\t100 000 ohms per volt\nD\t10 000 ohms per volt",
"children": [
{
"content": "> Voltmeter sensitivity in ohms per volt: i.e., the full-scale reading times the sensitivity yields total instrument resistance. Given total resistance, sensitivity can be computed as resistance divided by full-scale voltage reading: e.g., a total of 150 000 ohms for a voltmeter reading 150 volts is a sensitivity of 1000 ohms per volt.."
}
]
}
]
},
{
"content": "**Voltmeters** use large **bias resistors** in series with the movement to reduce the load of the meter on the circuit under test.\n\nTo *increase* the range of a voltmeter, a *greater* bias resistance is used to reduce the current flow to a value within the meter's range.",
"children": [
{
"content": "A-3-6-3 (D) A **voltmeter** having a range of 150 volts and an internal resistance of 150 000 ohms is to be extended to read 750 volts. The required multiplier resistor would have a value of:\nA\t1 500 ohms\nB\t750 000 ohms\nC\t1 200 000 ohms\nD\t600 000 ohms",
"children": [
{
"content": "> Extending the range of a voltmeter supposes placing a suitable multiplier resistor in series with the instrument: the multiplier resistance = total internal resistance times the multiplication factor from which we will first have deducted a quantity of one. For example, to turn a 150 volts meter, with an internal resistance of 150 000 ohms, to read 750 volts full scale is an increase of 5 times: the multiplier resistor = 150 000 times 4 (i.e., 5 minus 1) = 600 000 ohms. Method B: current for full-scale reading = 150 volts divided by 150 000 ohms = 1 milliampere. The total resistance that would allow 1 milliampere under 750 volts = 750 000 ohms. Deduct the internal resistance from this value to determine the multiplier resistor."
}
]
},
{
"content": "A-3-6-2 (C) A moving-coil milliammeter having a full-scale deflection of 1 mA and an internal resistance of 0.5 ohms is to be converted to a **voltmeter** of 20 volts full-scale deflection. It would be necessary to insert a:\nA\tshunt resistance of 19 999.5 ohms\nB\tshunt resistance of 19.5 ohms\nC\tseries resistance of 19 999.5 ohms\nD\tseries resistance of 1 999.5 ohms",
"children": [
{
"content": "> Turning an ammeter into a voltmeter supposes inserting a suitable resistor in series with the instrument. For a current of 1 milliampere to flow under 20 volts, Ohm's Law tells us that a total resistance of 20 000 ohms is required. Subtract the internal resistance from that number and the actual series resistance needed is 19 999.5 ohms."
}
]
},
{
"content": "A-3-6-8 (B) What happens inside a multimeter when you switch it from a lower to a higher **voltage** range?\nA\tResistance is added in parallel with the meter\nB\tResistance is **added** in **series** with the meter\nC\tResistance is reduced in series with the meter\nD\tResistance is reduced in parallel with the meter",
"children": [
{
"content": "> Extending the range of a voltmeter supposes placing a suitable multiplier resistor in series with the instrument; the higher the series resistance, the higher the voltage needed to obtain full-scale deflection on the meter."
}
]
}
]
}
]
},
{
"content": "Wattmeters measure power.",
"children": [
{
"content": "Wattmeters inductively with a torroidal coil surroundnign the feedline. The sampled signal is rectified down to DC, and the resulting voltage/current shown on a meter."
},
{
"content": "RF wattmeters are connected at the transmitter output.",
"children": [
{
"content": "A-3-6-10 (D) Where should an RF wattmeter be connected for the most accurate readings of transmitter output power?\nA\tOne-half wavelength from the transmitter output\nB\tOne-half wavelength from the antenna feed point\nC\tAt the antenna feed point\nD\tAt the **transmitter output** connector\n> Measuring right at the transmitter output connector removes any line losses from the measurement."
}
]
},
{
"content": "They must have the same **impedance** as the rest of the signal chain; typically 50 ohms.",
"children": [
{
"content": "A-3-6-11 (D) At what line impedance do most RF wattmeters usually operate?\nA\t25 ohms\nB\t100 ohms\nC\t300 ohms\nD\t50 ohms\n> In-line RF wattmeters are designed to work with the most common Characteristic Impedance in radio work: 50 ohms."
}
]
}
]
}
]
},
{
"content": "{L07} Oscillators.",
"children": [
{
"content": "Oscillators depend on **positive feedback** to reinforce a signal at a single frequency.",
"children": [
{
"content": "A-5-1-9 (C) A circuit depending on positive feedback for its operation would be a:\nA\tdetector\nB\taudio amplifier\nC\tvariable-frequency **oscillator**\nD\tmixer",
"children": [
{
"content": "> An oscillator, fixed or variable, is an amplifier with a positive feedback path from output to input used to start and maintain oscillation."
}
]
}
]
},
{
"content": "The exam deals with three types of oscillators. These are:\n* The **Hartley** oscillator, which is distinguished by a **tapped coil** (inductive divider),\n* the **Colpitts** oscillator, distinguished by a **capacitive divider**, and also\n* the **Pierce** oscillator, which uses a **crystal** with capacitive feedback. ",
"children": [
{
"content": "The Hartley and Colpitts oscillators both use a resonant [LC tank circuit](https://www.electronics-tutorials.ws/oscillator/oscillators.html).\n* The Hartley oscillator uses a tapped coil in the tank circuit.\n* The Colpitts oscillator uses capacitive divider for feedback coupling.",
"children": [
{
"content": "In a [Hartley oscillator](https://www.electronics-tutorials.ws/oscillator/hartley.html), the feedback is coupled back in to the input through a tapped coil.\n\n![](https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/oscillator-osc6.gif)\n",
"children": [
{
"content": "A-5-1-1 (C) How is the positive feedback coupled to the input in a Hartley oscillator?\nA\tThrough link coupling\nB\tThrough a neutralizing capacitor\nC\tThrough a **tapped coil**\nD\tThrough a capacitive divider",
"children": [
{
"content": "> Hartley = a tap on the inductor of the tuned circuit permits inserting positive feedback from output to input. Colpitts = the inductor tap of the Hartley is replaced by two series capacitors in a capacitive divider configuration. Relatively large capacitor values, when compared to the Hartley, mean less influence from internal capacitance changes in the device, hence stability. Pierce = derived from the Colpitts, a piezoelectric crystal replaces the tuned circuit. Capacitive coupling maintains oscillation."
}
]
}
]
},
{
"content": "A [Colpitts oscillator](https://www.electronics-tutorials.ws/oscillator/colpitts.html) uses a capacitive divider.\n![](https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/oscillator-osc13.gif)",
"children": [
{
"content": "A-5-1-6 (D) Positive feedback from a **capacitive divider** indicates the oscillator type is:\nA\tPierce\nB\tHartley\nC\tMiller\nD\tColpitts",
"children": [
{
"content": "> Hartley = a tap on the inductor of the tuned circuit permits inserting positive feedback from output to input. Colpitts = the inductor tap of the Hartley is replaced by two series capacitors in a capacitive divider configuration. Relatively large capacitor values, when compared to the Hartley, mean less influence from internal capacitance changes in the device, hence stability. Pierce = derived from the Colpitts, a piezoelectric crystal replaces the tuned circuit. Capacitive coupling maintains oscillation."
}
]
},
{
"content": "A-5-1-2 (B) How is positive feedback coupled to the input in a Colpitts oscillator?\nA\tThrough a link coupling\nB\tThrough a **capacitive divider**\nC\tThrough a tapped coil\nD\tThrough a neutralizing capacitor",
"children": [
{
"content": "> Hartley = a tap on the inductor of the tuned circuit permits inserting positive feedback from output to input. Colpitts = the inductor tap of the Hartley is replaced by two series capacitors in a capacitive divider configuration. Relatively large capacitor values, when compared to the Hartley, mean less influence from internal capacitance changes in the device, hence stability. Pierce = derived from the Colpitts, a piezoelectric crystal replaces the tuned circuit. Capacitive coupling maintains oscillation."
}
]
}
]
}
]
},
{
"content": "A [Pierce oscillator](https://www.electronics-tutorials.ws/oscillator/crystal.html) replaces the LC tank circuit with a **crystal**. It uses series **capacitive** feedback coupling.\n\n",
"children": [
{
"content": "![](https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/oscillator-osc32.gif)\n"
},
{
"content": "A-5-1-11 (A) In an oscillator where positive feedback is provided through a capacitor in series with a **crystal**, that type of oscillator is a:\nA\t**Pierce**\nB\tColpitts\nC\tHartley\nD\tFranklin",
"children": [
{
"content": "> Hartley = a tap on the inductor of the tuned circuit permits inserting positive feedback from output to input. Colpitts = the inductor tap of the Hartley is replaced by two series capacitors in a capacitive divider configuration. Relatively large capacitor values, when compared to the Hartley, mean less influence from internal capacitance changes in the device, hence stability. Pierce = derived from the Colpitts, a piezoelectric crystal replaces the tuned circuit. Capacitive coupling maintains oscillation."
}
]
},
{
"content": "A-5-1-8 (D) In an oscillator circuit where positive feedback is obtained through a single capacitor in series with the **crystal**, the type of oscillator is:\nA\tColpitts\nB\tHartley\nC\tMiller\nD\t**Pierce**",
"children": [
{
"content": "> Hartley = a tap on the inductor of the tuned circuit permits inserting positive feedback from output to input. Colpitts = the inductor tap of the Hartley is replaced by two series capacitors in a capacitive divider configuration. Relatively large capacitor values, when compared to the Hartley, mean less influence from internal capacitance changes in the device, hence stability. Pierce = derived from the Colpitts, a piezoelectric crystal replaces the tuned circuit. Capacitive coupling maintains oscillation."
}
]
},
{
"content": "A-5-1-3 (A) How is positive feedback coupled to the input in a **Pierce** oscillator?\nA\tThrough **capacitive** coupling\nB\tThrough a neutralizing capacitor\nC\tThrough link coupling\nD\tThrough a tapped coil",
"children": [
{
"content": "> Hartley = a tap on the inductor of the tuned circuit permits inserting positive feedback from output to input. Colpitts = the inductor tap of the Hartley is replaced by two series capacitors in a capacitive divider configuration. Relatively large capacitor values, when compared to the Hartley, mean less influence from internal capacitance changes in the device, hence stability. Pierce = derived from the Colpitts, a piezoelectric crystal replaces the tuned circuit. Capacitive coupling maintains oscillation."
}
]
}
]
},
{
"content": "**Crystal oscillators** are very stable narrow bandwidth, and high Q",
"children": [
{
"content": "Very frequency stable.",
"children": [
{
"content": "A-2-11-4 (C) The main advantage of a crystal oscillator over a tuned LC oscillator is:\nA\tfreedom from harmonic emissions\nB\tsimplicity\nC\tmuch greater frequency **stability**\nD\tlonger life under severe operating use",
"children": [
{
"content": "> Piezoelectric crystals behave like tuned circuits with an extremely high \"Q\" (\"Quality Factor\", in excess of 25 000). Their accuracy and stability are outstanding."
}
]
}
]
},
{
"content": "Multiples of the crystal frequency can be exploited as overtone oscilator",
"children": [
{
"content": "A-2-11-8 (B) **Crystals** are sometimes used in a circuit which has an output close to an integral **multiple** of the crystal frequency. This circuit is called:\nA\ta crystal ladder\nB\tan **overtone oscillator**\nC\ta crystal multiplier\nD\ta crystal lattice",
"children": [
{
"content": "> Key word: MULTIPLE. Crystals are capable of resonance either at a fundamental frequency depending on their physical dimensions or at overtone frequencies near odd-integer multiples (3rd, 5th, 7th, etc.) of the fundamental. In a filter, crystals are used at their fundamental frequencies; the crystal lattice filter and the crystal ladder filter are two typical configurations. Crystal oscillators can be designed to work on a fundamental or overtone resonance; crystals are manufactured accordingly."
}
]
}
]
},
{
"content": "Not a source of high power signals.",
"children": [
{
"content": "A-2-11-9 (B) Which of the following properties does **not** apply to a crystal when used in an oscillator circuit?\nA\tGood frequency accuracy\nB\t**High power output**\nC\tGood frequency stability\nD\tVery low noise because of high Q",
"children": [
{
"content": "> The piezoelectric property of quartz is two-fold: apply mechanical stress to a crystal and it produces a small electrical field; subject quartz to an electrical field and the crystal changes dimensions slightly. Crystals are capable of resonance either at a fundamental frequency depending on their physical dimensions or at overtone frequencies near odd-integer multiples (3rd, 5th, 7th, etc.). Piezoelectric crystals can serve as filters because of their extremely high \"Q\" (> 25 000) or as stable, noise-free and accurate frequency references."
}
]
}
]
}
]
}
]
},
{
"content": "The purpose of an oscillator is to provide a **stable** signal that is free of frequency drift."
},
{
"content": "* Colpitts oscillators use **large** capacitors in the capacitance divider that exhibit comparatively little variation over temperature.",
"children": [
{
"content": "A-5-1-4 (D) Why is the **Colpitts** oscillator circuit commonly used in a **VFO**?\nA\tIt can be used with or without crystal lock-in\nB\tThe frequency is a linear function with load impedance\nC\tIt has high output power\nD\tIt is **stable**",
"children": [
{
"content": "> Hartley = a tap on the inductor of the tuned circuit permits inserting positive feedback from output to input. Colpitts = the inductor tap of the Hartley is replaced by two series capacitors in a capacitive divider configuration. Relatively large capacitor values, when compared to the Hartley, mean less influence from internal capacitance changes in the device, hence stability. Pierce = derived from the Colpitts, a piezoelectric crystal replaces the tuned circuit. Capacitive coupling maintains oscillation."
}
]
}
]
},
{
"content": "* *Reference* oscillators that feed [phase-locked loops](https://www.electronics-notes.com/articles/radio/pll-phase-locked-loop/tutorial-primer-basics.php) must **stable** to reduce the [phase noise](https://www.analog.com/media/en/analog-dialogue/volume-52/number-3/phase-locked-loop-pll-fundamentals.pdf) produced.",
"children": [
{
"content": "A-5-1-5 (C) Why must a very **stable** reference oscillator be used as part of a phase-locked loop (PLL) frequency synthesizer?\nA\tAny amplitude variations in the reference oscillator signal will prevent the loop from changing frequency\nB\tAny amplitude variations in the reference oscillator signal will prevent the loop from locking to the desired signal\nC\tAny phase variations in the reference oscillator signal will produce phase noise in the synthesizer output\nD\tAny phase variations in the reference oscillator signal will produce harmonic distortion in the modulating signal",
"children": [
{
"content": "> Key words: PHASE-LOCKED. As the name implies, a PLL synthesizer includes a voltage-controlled oscillator (VCO) whose output is constantly compared to a stable crystal reference. If the phase of the output signal begins to lead or lag the reference (a phase error), a correction is applied to the oscillator tuning. If the reference is noisy or subject to phase jitter, the output is similarly corrupted."
}
]
}
]
},
{
"content": "* Where feedback is capacitively coupled, [**mica** capacitors](https://www.google.com/search?tbm=isch&source=hp&biw=1280&bih=734&ei=kgUaXtX4IIfV-gSX1Ko4&q=mica+capacitor+radio&oq=mica+capacitor+radio&gs_l=img.3...2003.4557..4667...0.0..0.154.2004.3j16......0....1..gws-wiz-img.......0j0i131j0i24.Cs5j6CUcKQQ&ved=0ahUKEwjViZ38iPzmAhWHqp4KHReqCgcQ4dUDCAY&uact=5) are used for [stability over temperature](https://www.electronics-notes.com/articles/electronic_components/capacitors/silver-mica.php).",
"children": [
{
"content": "A-5-1-7 (D) In an RF oscillator circuit designed for high stability, the positive feedback is drawn from two capacitors connected in series. These two capacitors would most likely be:\nA\tceramic\nB\telectrolytics\nC\tMylar\nD\tsilver mica",
"children": [
{
"content": "> In an oscillator, stability is paramount. Silver Mica, NP0 (N-P-Zero, negative-positive-zero) ceramic and polystyrene capacitors are temperature-stable. The electrolytic is suitable as a filter or audio bypass. The plain ceramic capacitor is good for coupling or RF bypass."
}
]
}
]
}
]
},
{
"content": "{L09} Transmitters.\n",
"children": [
{
"content": "In the grounded grid triode amplifier"
},
{
"content": "final tubes",
"children": [
{
"content": "A-5-2-2 (B) The purpose of using a **centre-tap** return connection on the secondary of transmitting tube's **filament transformer** is to:\nA obtain optimum power output\nB prevent **modulation** of the emitted wave by the alternating current **filament supply**\nC reduce the possibility of harmonic emissions\nD keep the output voltage constant with a varying load",
"children": [
{
"content": "> When the cathode is simply the filament (a \"directly-heated cathode\"), the voltage drop across the filament (e.g., 6.3 volts AC) is in series with the cathode DC reference voltage: as an example, while one side of the filament might be at a certain DC voltage, the other extremity is at some other value, a value influenced by the AC voltage impressed on the filament. Electron flow is affected by an AC variation, hum results."
}
]
}
]
},
{
"content": "In the **grounded grid triode amplifier** ...\n\nAs the name suggests, the grid (screen) is connected to ground. Similar to a common-base BJT configuration.",
"children": [
{
"content": "![schematic from https://www.w8ji.com/grounded_grid_amplifiers.htm](https://www.w8ji.com/images/Amplifier/Tunedinput/tuned_5.gif) [enlarge](https://www.w8ji.com/images/Amplifier/Tunedinput/tuned_5.gif)"
},
{
"content": "[schematic](http://www.9h1mrl.org/ukrae/arc_cd/full/gfx/dwg/f4-17.gif)\n\n[from here](http://www.9h1mrl.org/ukrae/arc_cd/full/html/c4-1-13.htm)"
},
{
"content": "The **plate** is connected to the high voltage supply.",
"children": [
{
"content": "A-5-2-5 (C) In a grounded grid amplifier using a triode vacuum tube, the **plate** is connected to a radio frequency choke. The other end of the radio frequency choke connects to the:\nA\tground\nB\tB- (bias)\nC\t**B+ (high voltage)**\nD\tfilament voltage",
"children": [
{
"content": "> A grounded-grid amplifier runs with the grid at ground potential. The **cathode** is **above** RF ground and serves as the input. A DC bias is applied to the cathode via an RF choke. Positive voltage (B+) is supplied to the plate via an RF choke. The plate is the output, a blocking capacitor passes the RF out to the matching network. A transformer provides AC filament voltage. The heater (in an indirectly-heated cathode tube) is bypassed to ground so radiofrequency does not stray out on the filament supply lines. [ If a tube is directly-heated (no separate cathode), filament voltage is brought through a filament choke. The side of the choke connected to the transformer is bypassed to ground with two capacitors. ]"
}
]
}
]
},
{
"content": "The input is applied to the Cathode",
"children": [
{
"content": "A-5-2-3 (A) In a grounded grid amplifier using a triode vacuum tube, the input signal is applied to:\nA the cathode\nB the plate\nC the control grid\nD the filament leads",
"children": [
{
"content": "> A grounded-grid amplifier runs with the grid at ground potential. The cathode is above RF ground and serves as the input. A DC bias is applied to the cathode via an RF choke. Positive voltage (B+) is supplied to the plate via an RF choke. The plate is the output, a blocking capacitor passes the RF out to the matching network. A transformer provides AC filament voltage. The heater (in an indirectly-heated cathode tube) is bypassed to ground so radiofrequency does not stray out on the filament supply lines. [ If a tube is directly-heated (no separate cathode), filament voltage is brought through a filament choke. The side of the choke connected to the transformer is bypassed to ground with two capacitors. ]"
}
]
}
]
},
{
"content": "The plate (output) is connected via a (DC) blocking capacitor to the Pi network.",
"children": [
{
"content": "A-5-2-4 (B) In a grounded grid amplifier using a triode vacuum tube, the plate is connected to the pi-network through a:\nA\telectrolytic capacitor\nB\tblocking capacitor\nC\tby-pass capacitor\nD\ttuning capacitor",
"children": [
{
"content": "> A grounded-grid amplifier runs with the grid at ground potential. The cathode is above RF ground and serves as the input. A DC bias is applied to the cathode via an RF choke. Positive voltage (B+) is supplied to the plate via an RF choke. The plate is the output, a blocking capacitor passes the RF out to the matching network. A transformer provides AC filament voltage. The heater (in an indirectly-heated cathode tube) is bypassed to ground so radiofrequency does not stray out on the filament supply lines. [ If a tube is directly-heated (no separate cathode), filament voltage is brought through a filament choke. The side of the choke connected to the transformer is bypassed to ground with two capacitors. ]"
}
]
}
]
},
{
"content": "The filament is bridged by an RF bypass caps.",
"children": [
{
"content": "A-5-2-9 (C) In a grounded grid amplifier using a triode vacuum tube, each side of the **filament** is connected to a capacitor whose other end is connected to ground. These are:\nA\telectrolytic capacitors\nB\tblocking capacitors\nC\t**by-pass capacitors**\nD\ttuning capacitors",
"children": [
{
"content": "> A grounded-grid amplifier runs with the grid at ground potential. The cathode is above RF ground and serves as the input. A DC bias is applied to the cathode via an RF choke. Positive voltage (B+) is supplied to the plate via an RF choke. The plate is the output, a blocking capacitor passes the RF out to the matching network. A transformer provides AC filament voltage. The heater (in an indirectly-heated cathode tube) is bypassed to ground so radiofrequency does not stray out on the filament supply lines. [ If a tube is directly-heated (no separate cathode), filament voltage is brought through a filament choke. The side of the choke connected to the transformer is bypassed to ground with two capacitors. ]"
}
]
}
]
},
{
"content": "The plate voltage can be determined using the relation shiop betwwen voltage, current, and power; taking into account efficiency.\n\nFor example, P = V I so V = P / I",
"children": [
{
"content": "A-5-2-8 (D) In a grounded grid amplifier using a triode vacuum tube, what would be the approximate B+ voltage required for an output of 400 watts at 400 mA with approximately 50 percent efficiency?\nA\t500 volts\nB\t3000 volts\nC\t1000 volts\nD\t**2000 volts**",
"children": [
{
"content": "> 400 watts out at 50% efficiency supposes that 800 watts DC are needed. Power is voltage times current ; thus, voltage is power divided by current ; 800 watts divided by 0.4 ampere = 2000 volts."
}
]
}
]
},
{
"content": "The filament (heater) voltage is provided by a transformer.",
"children": [
{
"content": "A-5-2-7 (B) In a grounded grid amplifier using a triode vacuum tube, the secondary winding of a transformer is connected directly to the vacuum tube. This transformer provides:\nA\tScreen voltage\nB\t**filament voltage**\nC\tB- (bias)\nD\tB+ (high voltage)",
"children": [
{
"content": "> A grounded-grid amplifier runs with the grid at ground potential. The cathode is above RF ground and serves as the input. A DC bias is applied to the cathode via an RF choke. Positive voltage (B+) is supplied to the plate via an RF choke. The plate is the output, a blocking capacitor passes the RF out to the matching network. A transformer provides AC filament voltage. The heater (in an indirectly-heated cathode tube) is bypassed to ground so radiofrequency does not stray out on the filament supply lines. [ If a tube is directly-heated (no separate cathode), filament voltage is brought through a filament choke. The side of the choke connected to the transformer is bypassed to ground with two capacitors. ]"
}
]
}
]
},
{
"content": "The cathode is negative-biased using the **B-** supply.",
"children": [
{
"content": "A-5-2-6 (A) In a grounded grid amplifier using a triode vacuum tube, the **cathode** is connected to a radio frequency choke. The other end of the radio frequency choke connects to the:\nA\t**B- (bias)**\nB\tground\nC\tfilament voltage\nD\tB+ (high voltage)",
"children": [
{
"content": "> A grounded-grid amplifier runs with the grid at ground potential. The cathode is above RF ground and serves as the input. A DC bias is applied to the cathode via an RF choke. Positive voltage (B+) is supplied to the plate via an RF choke. The plate is the output, a blocking capacitor passes the RF out to the matching network. A transformer provides AC filament voltage. The heater (in an indirectly-heated cathode tube) is bypassed to ground so radiofrequency does not stray out on the filament supply lines. [ If a tube is directly-heated (no separate cathode), filament voltage is brought through a filament choke. The side of the choke connected to the transformer is bypassed to ground with two capacitors. ]"
}
]
}
]
}
]
},
{
"content": "The **final matching network** matches the impedance of the tubes to the impedance of the antenna system for efficient power transfer.",
"children": [
{
"content": "A-5-2-1 (D) The output tuning controls on a transmitter power amplifier with an adjustable PI network:\nA allow switching to different antennas\nB reduce the possibility of cross-modulation in adjunct receivers\nC are involved with frequency multiplication in the previous stage\nD allow efficient transfer of power to the antenna",
"children": [
{
"content": "> Tube power amplifiers always include a matching network to match the high impedance of the tube to the antenna system impedance. As always, impedance match is all about maximum power transfer."
}
]
}
]
},
{
"content": "simple 2-stage CW transmitter",
"children": [
{
"content": "A CW transmimtter consists of an oscillator stage and a power amplifier stage.",
"children": [
{
"content": "A-5-1-10 (A) An apparatus with an oscillator and a class C amplifier would be:\nA\ta two-stage CW transmitter\nB\ta fixed-frequency single-sideband transmitter\nC\ta two-stage frequency-modulated transmitter\nD\ta two-stage regenerative receiver",
"children": [
{
"content": "> A simple two-stage CW transmitter comprises an oscillator and a Class-C power amplifier. A transformer at the output of the oscillator serves the dual purpose of tuned circuit and coupling to the next stage. The DC supply to the final amplifier is bypassed to ground with a capacitor and decoupled through an RF choke so RF is kept out of the supply."
}
]
}
]
},
{
"content": "![](https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1946/07/page16/fig1.jpg)\n\n[schematic](https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1946/07/page16/fig1.jpg), [source](https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1946/07/page16/index.html)"
},
{
"content": "The first stage is an oscillator."
},
{
"content": "The second stage is a power amplifier.",
"children": [
{
"content": "A-5-3-3 (C) In a simple 2 stage CW transmitter, the transistor in the **second stage** would act as:\nA\tthe master oscillator\nB\tan audio oscillator\nC\ta **power amplifier**\nD\ta frequency multiplier",
"children": [
{
"content": "> A simple two-stage CW transmitter comprises an oscillator and a Class-C power amplifier. A transformer at the output of the oscillator serves the dual purpose of tuned circuit and coupling to the next stage. The DC supply to the final amplifier is bypassed to ground with a capacitor and decoupled through an RF choke so RF is kept out of the supply."
}
]
}
]
},
{
"content": "Note the LC pi-network after the amplifer stage. This is a low-pass filter.",
"children": [
{
"content": "A-5-3-2 (A) In a simple 2 stage CW transmitter, current to the collector of the transistor in the class C **amplifier stage** flows through a radio frequency choke (RFC) and a tapped inductor. The RFC, on the tapped inductor side, is also connected to **grounded capacitors**. The purpose of the RFC and capacitors is to:\nA\tform a **low-pass filter**\nB\tprovide negative feedback\nC\tform a key-click filter\nD\tform a RF-tuned circuit",
"children": [
{
"content": "> A simple two-stage CW transmitter comprises an oscillator and a Class-C power amplifier. A transformer at the output of the oscillator serves the dual purpose of tuned circuit and coupling to the next stage. The DC supply to the final amplifier is bypassed to ground with a capacitor and decoupled through an RF choke so RF is kept out of the supply."
}
]
}
]
},
{
"content": "there is a tuned circuit that is inductively coupled",
"children": [
{
"content": "A-5-3-1 (C) In a simple 2 stage CW transmitter circuit, the oscillator stage and the class C amplifier stage are **inductively coupled** by a RF transformer. Another role of the RF transformer is to:\nA\tprovide the necessary feedback for oscillation\nB\tact as part of a balanced mixer\nC\tbe part of a tuned circuit\nD\tact as part of a pi filter",
"children": [
{
"content": "> A simple two-stage CW transmitter comprises an oscillator and a Class-C power amplifier. A transformer at the output of the oscillator serves the dual purpose of tuned circuit and coupling to the next stage. The DC supply to the final amplifier is bypassed to ground with a capacitor and decoupled through an RF choke so RF is kept out of the supply."
}
]
}
]
},
{
"content": "A **buffer stage** may be incorporated between the oscillator and PA stages to eliminate chirp, which is caused by perturbation of the oscillator frequency as its loaded down by the PA. ",
"children": [
{
"content": "A-5-3-4 (A) An advantage of keying the buffer stage in a transmitter is that:\nA\tchanges in oscillator frequency are less likely\nB\tkey clicks are eliminated\nC\tthe radiated bandwidth is restricted\nD\thigh RF voltages are not present",
"children": [
{
"content": "> Keying a subsequent stage provides the oscillator with a fairly constant load (isolation) and allows it to run continuously for better stability."
}
]
}
]
},
{
"content": "Furthermore, **tuned circuit filters** may be used between stages to prevent the passage of **unwanted harmonics**.",
"children": [
{
"content": "A-5-2-11 (C) Harmonics produced in an early stage of a transmitter may be reduced in a later stage by:\nA\tgreater input to the final stage\nB\ttransistors instead of tubes\nC\t**tuned circuit coupling** between stages\nD\tlarger value coupling capacitors",
"children": [
{
"content": "> Key words: STAGES. Resonant circuits in the coupling between stages help convey only the operating frequency. Larger coupling capacitors would pass the harmonics more readily."
}
]
}
]
}
]
},
{
"content": "In a power amplifier, there may be some feedback from the output to the input. This feedback may cause \"parasitic\" oscillation in the absence of a neutralizing circuit to cancel it out.",
"children": [
{
"content": "Unwanted, **parasitic** oscillations may occur if the feedback is resonant at these frequencies.",
"children": [
{
"content": "A-5-3-9 (A) **Parasitic oscillations** would tend to occur mostly in:\nA\t**RF power output stages**\nB\thigh gain audio output stages\nC\thigh voltage rectifiers\nD\tmixer stages",
"children": [
{
"content": "> Undesired positive feedback in an RF amplifier causes parasitic oscillations: the amplifier becomes an oscillator. Inter-electrode capacitance (e.g., plate-to-grid), coupling from output to input, stray inductance or capacitance can start up oscillations. Neutralization is the process of cancelling positive-feedback paths. To test a tube amplifier for parasitic oscillations, connect nothing to the input and output terminals, apply DC power, monitor grid and plate current while slowly varying the controls on the output tuning network; if grid current develops or plate current changes, oscillations are present."
}
]
},
{
"content": "A-5-3-8 (B) **Parasitic oscillations** are usually generated due to:\nA\ta mismatch between power amplifier and transmission line\nB\t**accidental resonant frequencies** in the power amplifier\nC\tharmonics from some earlier multiplier stage\nD\texcessive drive or excitation to the power amplifier",
"children": [
{
"content": "> Undesired positive feedback in an RF amplifier causes parasitic oscillations: the amplifier becomes an oscillator. Inter-electrode capacitance (e.g., plate-to-grid), coupling from output to input, stray inductance or capacitance can start up oscillations. Neutralization is the process of cancelling positive-feedback paths. To test a tube amplifier for parasitic oscillations, connect nothing to the input and output terminals, apply DC power, monitor grid and plate current while slowly varying the controls on the output tuning network; if grid current develops or plate current changes, oscillations are present."
}
]
},
{
"content": "A-5-3-11 (B) **Parasitic oscillations** in an RF power amplifier may be caused by:\nA\texcessive harmonic production\nB\tlack of **neutralization**\nC\toverdriven stages\nD\tpoor voltage regulation",
"children": [
{
"content": "> Undesired positive feedback in an RF amplifier causes parasitic oscillations: the amplifier becomes an oscillator. Inter-electrode capacitance (e.g., plate-to-grid), coupling from output to input, stray inductance or capacitance can start up oscillations. Neutralization is the process of cancelling positive-feedback paths. To test a tube amplifier for parasitic oscillations, connect nothing to the input and output terminals, apply DC power, monitor grid and plate current while slowly varying the controls on the output tuning network; if grid current develops or plate current changes, oscillations are present."
}
]
}
]
},
{
"content": "A **neutralizing circuit** cancels unwanted feedback signals coupled from the output of power amplifier to the input.",
"children": [
{
"content": "A-5-3-7 (C) What is the reason for **neutralizing** the final amplifier stage of a transmitter?\nA\tTo cut off the final amplifier during standby periods\nB\tTo keep the carrier on frequency\nC\tTo eliminate **parasitic oscillations**\nD\tTo limit the modulation index",
"children": [
{
"content": "> Undesired positive feedback in an RF amplifier causes parasitic oscillations: the amplifier becomes an oscillator. Inter-electrode capacitance (e.g., plate-to-grid), coupling from output to input, stray inductance or capacitance can start up oscillations. Neutralization is the process of cancelling positive-feedback paths. To test a tube amplifier for parasitic oscillations, connect nothing to the input and output terminals, apply DC power, monitor grid and plate current while slowly varying the controls on the output tuning network; if grid current develops or plate current changes, oscillations are present."
}
]
},
{
"content": "A-5-3-6 (D) What does a **neutralizing circuit** do in an RF amplifier?\nA\tIt eliminates AC hum from the power supply\nB\tIt reduces incidental grid modulation\nC\tIt controls differential gain\nD\tIt **cancels** the effects of positive **feedback**",
"children": [
{
"content": "> Undesired positive feedback in an RF amplifier causes parasitic oscillations: the amplifier becomes an oscillator. Inter-electrode capacitance (e.g., plate-to-grid), coupling from output to input, stray inductance or capacitance can start up oscillations. Neutralization is the process of cancelling positive-feedback paths. To test a tube amplifier for parasitic oscillations, connect nothing to the input and output terminals, apply DC power, monitor grid and plate current while slowly varying the controls on the output tuning network; if grid current develops or plate current changes, oscillations are present."
}
]
},
{
"content": "A-5-3-5 (D) As a power amplifier is tuned, what reading on its grid current meter indicates the best neutralization?\nA\tMinimum grid current\nB\tMaximum grid current\nC\tA maximum change in grid current as the output circuit is changed\nD\tA minimum change in grid current as the output circuit is changed",
"children": [
{
"content": "> Undesired positive feedback in an RF amplifier causes parasitic oscillations: the amplifier becomes an oscillator. Inter-electrode capacitance (e.g., plate-to-grid), coupling from output to input, stray inductance or capacitance can start up oscillations. Neutralization is the process of cancelling positive-feedback paths. To test a tube amplifier for parasitic oscillations, connect nothing to the input and output terminals, apply DC power, monitor grid and plate current while slowly varying the controls on the output tuning network; if grid current develops or plate current changes, oscillations are present."
}
]
},
{
"content": "A-5-3-10 (D) Why is neutralization necessary for some vacuum-tube amplifiers?\nA\tTo reduce grid-to-cathode leakage\nB\tTo cancel AC hum from the filament transformer\nC\tTo reduce the limits of loaded Q\nD\tTo cancel oscillation caused by the effects of interelectrode capacitance",
"children": [
{
"content": "> Undesired positive feedback in an RF amplifier causes parasitic oscillations: the amplifier becomes an oscillator. Inter-electrode capacitance (e.g., plate-to-grid), coupling from output to input, stray inductance or capacitance can start up oscillations. Neutralization is the process of cancelling positive-feedback paths. To test a tube amplifier for parasitic oscillations, connect nothing to the input and output terminals, apply DC power, monitor grid and plate current while slowly varying the controls on the output tuning network; if grid current develops or plate current changes, oscillations are present."
}
]
}
]
}
]
},
{
"content": "safety",
"children": [
{
"content": "A-5-2-10 (B) After you have opened a VHF power amplifier to make internal tuning adjustments, what should you do before you turn the amplifier on?\nA\tRemove all amplifier shielding to ensure maximum cooling\nB\tBe certain all amplifier shielding is fastened in place\nC\tMake sure that the power interlock switch is bypassed so you can test the amplifier\nD\tBe certain no antenna is attached so that you will not cause any interference",
"children": [
{
"content": "> Running a VHF or UHF power amplifier without shielding presents a safety risk in terms of RF exposure."
}
]
}
]
},
{
"content": "SSB",
"children": [
{
"content": "balanced modulator",
"children": [
{
"content": "The balmod suppresses the carrier, and produces double-sideband.",
"children": [
{
"content": "A-5-4-1 (C) What type of signal does a balanced modulator produce?\nA\tFull carrier\nB\tSingle sideband, suppressed carrier\nC\t**Double sideband**, **suppressed carrier**\nD\tFM with balanced deviation",
"children": [
{
"content": "> One method of producing SSB is a Balanced Modulator followed by a filter. The modulator takes in a fixed-frequency RF signal and mixes it with audio from the speech amplifier. The modulator is said to be balanced because the two original inputs are not present at the output: carrier suppression has taken place. Present, however, are a lower and upper sideband. A subsequent filter selects one of the sidebands to complete the creation of a single sideband suppressed-carrier signal. Note that there is no RF output when no audio is applied."
}
]
},
{
"content": "A-5-4-3 (B) Carrier suppression in a single-sideband transmitter takes place in:\nA\tthe frequency multiplier stage\nB\tthe **balanced modulator** stage\nC\tthe carrier decouple stage\nD\tthe mechanical filter",
"children": [
{
"content": "> One method of producing SSB is a Balanced Modulator followed by a filter. The modulator takes in a fixed-frequency RF signal and mixes it with audio from the speech amplifier. The modulator is said to be balanced because the two original inputs are not present at the output: carrier suppression has taken place. Present, however, are a lower and upper sideband. A subsequent filter selects one of the sidebands to complete the creation of a single sideband suppressed-carrier signal. Note that there is no RF output when no audio is applied."
}
]
}
]
},
{
"content": "A following filter remoevs the unwanted sideband.",
"children": [
{
"content": "A-5-4-2 (C) How can a single-sideband phone signal be produced?\nA\tBy using a loop modulator followed by a mixer\nB\tBy using a reactance modulator followed by a mixer\nC\tBy using a balanced modulator followed by a **filter**\nD\tBy driving a product detector with a DSB signal",
"children": [
{
"content": "> One method of producing SSB is a Balanced Modulator followed by a filter. The modulator takes in a fixed-frequency RF signal and mixes it with audio from the speech amplifier. The modulator is said to be balanced because the two original inputs are not present at the output: carrier suppression has taken place. Present, however, are a lower and upper sideband. A subsequent filter selects one of the sidebands to complete the creation of a single sideband suppressed-carrier signal. Note that there is no RF output when no audio is applied."
}
]
}
]
}
]
},
{
"content": "ssb power",
"children": [
{
"content": "Going from AM to SSB results in improvements *both* in terms of effective **transmit gain** (power more concentrated) and **receive gain** (narrower bandwidth signal includes less noise)",
"children": [
{
"content": "A-5-4-4 (C) Transmission with SSB, as compared to conventional AM transmission, results in:\nA\ta greater bandpass requirement in the receiver\nB\t3 dB gain in the transmitter\nC\t6 dB **gain in the transmitter** and 3 dB **gain in the receiver**\nD\t6 dB gain in the receiver",
"children": [
{
"content": "> Under noisy conditions, SSB can bring up to a 9 dB improvement over an AM signal of the same peak power. In AM, the Peak Envelope Power present in one of the two sidebands equals one fourth the carrier power: e.g., a 100-watt AM transmitter only packs 25 watts PEP in each sideband. SSB concentrates all the available power in one sideband alone: a 4 to 1 improvement or 6 dB. Using half the bandwidth on SSB reception, permits taking in only half of the noise at the receiver, an additional 3 dB improvement."
}
]
}
]
},
{
"content": "The carrier must be suppressed, which in practice means 40 dB below (a factor of 10,000).",
"children": [
{
"content": "A-5-4-10 (B) How much is the carrier suppressed below peak output power in a single-sideband phone transmission?\nA\tAt least 60 dB\nB\t**At least 40 dB**\nC\tNo more than 20 dB\nD\tNo more than 30 dB",
"children": [
{
"content": "> \"Most well-designed balanced modulators can provide between 30 and 50 dB of carrier suppression. ...The filter roll-off can be used to obtain an additional 20 dB of carrier suppression.\" (ARRL Handbook 1985)"
}
]
}
]
}
]
},
{
"content": "two-tone test",
"children": [
{
"content": "Two-tone test is a test of linearity for SSB transmissions.",
"children": [
{
"content": "A-5-4-6 (C) What kind of input signal is used to test the amplitude linearity of a single-sideband phone transmitter while viewing the output on an oscilloscope?\nA\tAn audio-frequency square wave\nB\tNormal speech\nC\t**Two audio-frequency sine waves**\nD\tAn audio-frequency sine wave",
"children": [
{
"content": "> A two-tone test permits verifying the linearity of an SSB transmitter. The test requires a generator producing two low-distortion non-harmonically related audio sine waves of equal amplitude. The frequencies must fall within the normal transmitter audio passband: e.g., 700 and 1900 Hz. A sample of the transmitter's output is observed on an oscilloscope while the tones are fed into the microphone input. Feeding an SSB transmitter with two equal-amplitude steady audio tones produces two equal-amplitude RF signals: total power is thus twice the power present in each RF signal."
}
]
},
{
"content": "A-5-4-9 (A) What measurement can be made of a single-sideband phone transmitter's amplifier by performing a **two-tone test** using an oscilloscope?\nA\tIts **linearity**\nB\tIts frequency deviation\nC\tIts percent of carrier phase shift\nD\tIts percent of frequency modulation",
"children": [
{
"content": "> A two-tone test permits verifying the linearity of an SSB transmitter. The test requires a generator producing two low-distortion non-harmonically related audio sine waves of equal amplitude. The frequencies must fall within the normal transmitter audio passband: e.g., 700 and 1900 Hz. A sample of the transmitter's output is observed on an oscilloscope while the tones are fed into the microphone input. Feeding an SSB transmitter with two equal-amplitude steady audio tones produces two equal-amplitude RF signals: total power is thus twice the power present in each RF signal."
}
]
}
]
},
{
"content": "The **peak** power of the output transmission is the integral of power spectrum. So, in the context of the two-tone test, where both input signals are the same power, the output is twice the power of either input signal.",
"children": [
{
"content": "A-5-4-5 (C) The **peak power** output of a single-sideband transmitter, when being tested by a two-tone generator is:\nA\tone-half of the RF peak output power of any of the tones\nB\tone-quarter of the RF peak output power of any of the tones\nC\t**twice** the RF power output of any of the tones\nD\tequal to the RF peak output power of any of the tones",
"children": [
{
"content": "> A two-tone test permits verifying the linearity of an SSB transmitter. The test requires a generator producing two low-distortion non-harmonically related audio sine waves of equal amplitude. The frequencies must fall within the normal transmitter audio passband: e.g., 700 and 1900 Hz. A sample of the transmitter's output is observed on an oscilloscope while the tones are fed into the microphone input. Feeding an SSB transmitter with two equal-amplitude steady audio tones produces two equal-amplitude RF signals: total power is thus twice the power present in each RF signal."
}
]
}
]
},
{
"content": "The test uses two **non-harmonically-related** tones. The output is observed in the time domain, on an **oscilloscope**.",
"children": [
{
"content": "A-5-4-7 (D) When testing the **amplitude linearity** of a single-sideband transmitter what audio tones are fed into the microphone input and on what kind of kind of instrument is the output observed?\nA\tTwo harmonically related tones are fed in, and the output is observed on an oscilloscope\nB\tTwo harmonically related tones are fed in, and the output is observed on a distortion analyzer\nC\tTwo non-harmonically related tones are fed in, and the output is observed on a distortion analyzer\nD\tTwo **non-harmonically** related tones are fed in, and the output is observed on an **oscilloscope**",
"children": [
{
"content": "> A two-tone test permits verifying the linearity of an SSB transmitter. The test requires a generator producing two low-distortion non-harmonically related audio sine waves of equal amplitude. The frequencies must fall within the normal transmitter audio passband: e.g., 700 and 1900 Hz. A sample of the transmitter's output is observed on an oscilloscope while the tones are fed into the microphone input. Feeding an SSB transmitter with two equal-amplitude steady audio tones produces two equal-amplitude RF signals: total power is thus twice the power present in each RF signal."
}
]
}
]
},
{
"content": "Any two audio tones may be used, but they must be within the transmitter audio passband, and should **not be harmonically related**",
"children": [
{
"content": "A-5-4-8 (A) What audio frequencies are used in a two-tone test of the linearity of a single-sideband phone transmitter?\nA\tAny two audio tones may be used, but they must be within the transmitter audio passband, and should **not be harmonically related**\nB\t20 Hz and 20 kHz tones must be used\nC\t1200 Hz and 2400 Hz tones must be used\nD\tAny two audio tones may be used, but they must be within the transmitter audio passband, and must be harmonically related",
"children": [
{
"content": "> A two-tone test permits verifying the linearity of an SSB transmitter. The test requires a generator producing two low-distortion non-harmonically related audio sine waves of equal amplitude. The frequencies must fall within the normal transmitter audio passband: e.g., 700 and 1900 Hz. A sample of the transmitter's output is observed on an oscilloscope while the tones are fed into the microphone input. Feeding an SSB transmitter with two equal-amplitude steady audio tones produces two equal-amplitude RF signals: total power is thus twice the power present in each RF signal."
}
]
}
]
}
]
},
{
"content": "ALC is a type of RF signal processing that prevents \"flat-topping\" of the transmitted signal due to over-driving the power amplifier.",
"children": [
{
"content": "A-5-4-11 (B) What is meant by **\"flat topping\"** in a single-sideband phone transmission?\nA\tThe transmitter's carrier is properly suppressed\nB\tSignal distortion caused by **excessive drive**\nC\tSignal distortion caused by insufficient collector current\nD\tThe transmitter's automatic level control is properly adjusted",
"children": [
{
"content": "> Flattening of the peaks is an extreme form of distortion where the output of the transmitter is incapable of reproducing the original pattern of the audio input on voice peaks. This is generally caused by excessive audio input to the transmitter: too much audio causes the amplifier stage to exceed its linear operation range. The purpose of the ALC (Automatic Level Control) is to prevent overdrive."
}
]
},
{
"content": "A-5-7-1 (A) Maintaining the peak RF output of a SSB transmitter at a relatively constant level requires a circuit called the:\nA\t**automatic level control (ALC)**\nB\tautomatic gain control (AGC)\nC\tautomatic output control (AOC)\nD\tautomatic volume control (AVC)",
"children": [
{
"content": "> Automatic Level Control (ALC) serves to prevent overdriving an amplifier. The ALC circuit samples the envelope (peak) of the RF output to develop a DC control voltage used to control the gain of an earlier stage. AGC and AVC are receiver circuits."
}
]
},
{
"content": "A-5-7-11 (B) Automatic Level Control (ALC) is another name for:\nA\tAF clipping\nB\t**RF compression**\nC\tAF compression\nD\tRF clipping",
"children": [
{
"content": "> Clipping places a hard limit on voltage swings. Compression is a reduction in gain when signal exceed a certain threshold. The ALC circuit samples the envelope (peak) of the RF output and produces a DC control voltage used to control the gain of an earlier stage when the output reaches a certain level."
}
]
}
]
}
]
},
{
"content": "Analog Signal processing",
"children": [
{
"content": "Audio signal processing takes place after the audio amp, and before the modulator.",
"children": [
{
"content": "A-5-6-9 (A) In most modern FM transmitters, to produce a better sound, a **compressor** and a **clipper** are placed:\nA\tbetween the **audio amplifier** and the **modulator**\nB\tbetween the multiplier and the PA\nC\tbetween the modulator and the oscillator\nD\tin the microphone circuit, before the audio amplifier",
"children": [
{
"content": "> In this context, compression and clipping are AUDIO processes aimed at maintaining high average deviation without exceeding a given peak value. Two answers can be readily scratched as they pertain to radiofrequency (RF) paths. The microphone circuit is not suitable as the audio level at that point is too low for a simple clipper."
}
]
}
]
},
{
"content": "The consequence of "
},
{
"content": "**Clipping**, or **peak-limiting** is a simple example of AF signal processing.",
"children": [
{
"content": "peak limiting",
"children": [
{
"content": "A-5-7-8 (B) Which of the following is **not** a method used for **peak limiting**, in a signal processor?\nA\tAF clipping\nB\t**Frequency clipping**\nC\tRF clipping\nD\tCompression",
"children": [
{
"content": "> The expression \"peak limiting\" entails limiting the amplitude. Compression, AF clipping and RF clipping are valid operations. There is no such thing as frequency clipping."
}
]
}
]
},
{
"content": "A-5-7-9 (B) What is the undesirable result of **AF clipping** in a speech processor?\nA\tReduction in peak amplitude\nB\tIncreased **harmonic distortion**\nC\tReduced average power\nD\tIncreased average power",
"children": [
{
"content": "> Audio frequency clipping abruptly stops voltage excursions at a certain level. This gives the audio a square wave appearance; square waves are rich in harmonics. AF clippers need to be followed by a low-pass filter to prevent harmonics from entering modulation stages. You may also eliminate the bad answers: \"reduction in peak amplitude\" is the object of clipping, \"increased average power\" is a result of clipping (softer passages are no longer dwarfed by the peaks), \"increased average power\" simply contradicts the previous answer."
}
]
},
{
"content": "A-5-7-10 (C) Which description is not correct? You are planning to build a speech processor for your transceiver. Compared to AF clipping, **RF clipping**:\nA\tis more expensive to implement\nB\tis more difficult to implement\nC\tis **easier to implement**\nD\thas less distortion",
"children": [
{
"content": "> Working at radio-frequencies is evidently more difficult and thus more expensive than dealing with audio frequencies. RF clipping is generally presumed to induce less distortion because any harmonics generated through clipping automatically end up outside the passband of subsequent filters. At audio frequencies, harmonics of the lower speech frequencies fall within the audio passband and can muddle the audio signal."
}
]
}
]
},
{
"content": "**Speech compression** makes the amplitude response non-linear; bringing up the bottom rather than limiting the top.",
"children": [
{
"content": "A-5-7-2 (C) Speech compression associated with SSB transmission implies:\nA\ta lower signal-to-noise ratio\nB\tcircuit level instability\nC\tfull amplification of low level signals and reducing or eliminating amplification of high level signals\nD\tfull amplification of high level signals and reducing or eliminating signals amplification of low level",
"children": [
{
"content": "> Audio compression maintains a high voice level despite variations in the voice signal incoming from a microphone. To produce a high average output without exceeding a certain peak value, low level signals need to be amplified while high level signals are passed along with little or no gain. [ compression is the automatic reduction of gain as the signal level increases beyond a pre-set level known as the threshold. ]"
}
]
}
]
},
{
"content": "A-5-7-7 (B) Which principle is **not** associated with **analog** signal processing?\nA\tClipping\nB\t**Frequency division**\nC\tCompression\nD\tBandwidth limiting",
"children": [
{
"content": "> Key words: NOT ASSOCIATED WITH ANALOG. Compression, bandwidth limiting and clipping can all be performed as analog processes. Frequency division requires a numerical computation."
}
]
}
]
},
{
"content": "FM",
"children": [
{
"content": "[About FM signals](https://www.electronics-notes.com/articles/radio/modulation/frequency-modulation-fm-sidebands-bandwidth.php)"
},
{
"content": "For the transmitted RF signal, the three important parameters to optimize together are \n* power, \n* deviation, and \n* stability.",
"children": [
{
"content": "A-5-6-10 (D) Three important parameters to be verified in an FM transmitter are:\nA\tdistortion, bandwidth and sideband power\nB\tmodulation, pre-emphasis and carrier suppression\nC\tfrequency stability, de-emphasis and linearity\nD\t**power**, frequency **deviation** and frequency **stability**",
"children": [
{
"content": "> Stability is paramount in all transmitters, frequency deviation ultimately determines bandwidth while linearity (absence of distortion) minimizes out-of-channel emissions. Carrier Suppression is a concern with SSB, pre-emphasis (FM transmitter) and de-emphasis (FM receiver) are simple resistor-capacitor networks."
}
]
}
]
},
{
"content": "When there is no modulation, the carrier sits at the at the **Center frequency**.",
"children": [
{
"content": "A-5-5-5 (B) When the transmitter is not modulated, or the amplitude of the modulating signal is zero, the frequency of the carrier is called its:\nA\tmodulating frequency\nB\t**centre frequency**\nC\tfrequency deviation\nD\tfrequency shift",
"children": [
{
"content": "> Centre Frequency is the transmitter output frequency in the absence of modulation. Frequency deviation and frequency shift both are synonyms for the offset in carrier frequency caused by modulation at a given instant. Modulating frequency relates to the audio frequency used for modulation."
}
]
}
]
},
{
"content": "**Deviation meters** multiply the modulation frequency by something called the modulation index.",
"children": [
{
"content": "A-5-5-8 (A) Some types of **deviation meters** work on the principle of:\nA\ta carrier null and multiplying the **modulation frequency** by the **modulation index**\nB\tdetecting the frequencies in the sidebands\nC\tthe amplitude of power in the sidebands\nD\ta carrier peak and dividing by the modulation index",
"children": [
{
"content": "> Certain Modulation Index values cause nulls at the centre carrier frequency: e.g., the Bessel function returns zero for the carrier component at Modulation Indices of 2.4048, 5.5201 or 8.6537 . Detecting a carrier null permits determining deviation as Modulation Index times modulating frequency. For example, with a tone of 905 hertz and deviation set at 4996 hertz (nearly 5 kHz), a null in the carrier will be observed because 4996 Hz deviation for a tone of 905 Hz is a Modulation Index of 5.52 . An all-mode receiver with a sharp filter permits observing the carrier component. The procedure could be used to set a transmitter or calibrate a home-made deviation meter.\n' Expressed to 8 decimal places, the first three indices producing Bessel nulls for J(0) are 2.40482556, 5.52007811 and 8.65372791."
}
]
},
{
"content": "A-5-5-9 (B) When using some **deviation meters**, it is important to know:\nA\tpass-band of the IF filter\nB\t**modulating frequency** and the **modulation index**\nC\tmodulation index\nD\tmodulating frequency\n",
"children": [
{
"content": "> Certain Modulation Index values cause nulls at the centre carrier frequency: e.g., the Bessel function returns zero for the carrier component at Modulation Indices of 2.4048, 5.5201 or 8.6537 . Detecting a carrier null permits determining deviation as Modulation Index times modulating frequency. For example, with a tone of 905 hertz and deviation set at 4996 hertz (nearly 5 kHz), a null in the carrier will be observed because 4996 Hz deviation for a tone of 905 Hz is a Modulation Index of 5.52 . An all-mode receiver with a sharp filter permits observing the carrier component. The procedure could be used to set a transmitter or calibrate a home-made deviation meter."
}
]
}
]
},
{
"content": "modulation index is the proportion by which the modulating frequency displaces the carrier frequency. It is given by:\n```\n f_dev\nM = -----\n f_mod\n```",
"children": [
{
"content": "For example, if a deviation of 3000 Hz results from a modulating frequency of 1000 Hz, this is a modulation index of\n`3000/1000 = 3`",
"children": [
{
"content": "A-5-5-1 (D) In an FM phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency, what is the modulation index, when the modulating frequency is 1000 Hz?\nA\t0.3\nB\t3000\nC\t1000\n**D\t3**",
"children": [
{
"content": "> Deviation = the amount of frequency shift, at a given instant, from the centre carrier frequency (e.g., plus or minus 5 kHz). Modulation Index = the ratio of deviation to modulating frequency for a particular audio frequency (both being expressed in the same units): e.g., 3 kHz deviation with 1 kHz audio represents a Modulation Index of 3. Deviation Ratio = the ratio of maximum deviation to the maximum modulating frequency: e.g. maximum deviation of 5 kHz with a highest modulating frequency of 3 kHz is a Deviation Ratio of 1.66 ."
}
]
}
]
},
{
"content": "For example, if there's a deviation of 6 kHz resulting from a modulating frequency of 2 kHz, the modulation index is\n\n`6/2 = 3` times greater than than the modulating frequency",
"children": [
{
"content": "A-5-5-2 (A) What is the modulation index of an FM phone transmitter producing an instantaneous carrier deviation of 6 kHz when modulated with a 2 kHz modulating frequency?\nA\t**3**\nB\t0.333\nC\t2000\nD\t6000",
"children": [
{
"content": "> Deviation = the amount of frequency shift, at a given instant, from the centre carrier frequency (e.g., plus or minus 5 kHz). Modulation Index = the ratio of deviation to modulating frequency for a particular audio frequency (both being expressed in the same units): e.g., 3 kHz deviation with 1 kHz audio represents a Modulation Index of 3. Deviation Ratio = the ratio of maximum deviation to the maximum modulating frequency: e.g. maximum deviation of 5 kHz with a highest modulating frequency of 3 kHz is a Deviation Ratio of 1.66 ."
}
]
}
]
}
]
},
{
"content": "Deviation ratio is basically the same thing, but calculated at the maximum extent of either: \n```\n dev_max\nDR = -------\n mod_max\n```",
"children": [
{
"content": "For example:"
},
{
"content": "If the maximum deviation is 5 kHz, and the maximum modulating signal is 3 kHz, then the deviation ratio is\n\n5/3 = about 1.5 ",
"children": [
{
"content": "A-5-5-3 (A) What is the deviation ratio of an FM phone transmitter having a maximum frequency swing of plus or minus 5 kHz and accepting a maximum modulation rate of 3 kHz?\nA\t1.66\nB\t60\nC\t0.16\nD\t0.6",
"children": [
{
"content": "> Deviation = the amount of frequency shift, at a given instant, from the centre carrier frequency (e.g., plus or minus 5 kHz). Modulation Index = the ratio of deviation to modulating frequency for a particular audio frequency (both being expressed in the same units): e.g., 3 kHz deviation with 1 kHz audio represents a Modulation Index of 3. **Deviation Ratio** = the ratio of maximum deviation to the maximum modulating frequency: e.g. maximum deviation of 5 kHz with a highest modulating frequency of 3 kHz is a Deviation Ratio of 1.66 ."
}
]
}
]
},
{
"content": "The deviation ratio if the maximum deviation is 7.5 kHz and the maximum modulating frequency is 3.5 kHz, then the deviation ratio is\n\n7.5/3.5 = about 2",
"children": [
{
"content": "A-5-5-4 (D) What is the deviation ratio of an FM phone transmitter having a maximum frequency swing of plus or minus 7.5 kHz and accepting a maximum modulation rate of 3.5 kHz?\nA\t0.47\nB\t47\nC\t0.214\nD\t2.14",
"children": [
{
"content": "> Deviation = the amount of frequency shift, at a given instant, from the centre carrier frequency (e.g., plus or minus 5 kHz). Modulation Index = the ratio of deviation to modulating frequency for a particular audio frequency (both being expressed in the same units): e.g., 3 kHz deviation with 1 kHz audio represents a Modulation Index of 3. Deviation Ratio = the ratio of maximum deviation to the maximum modulating frequency: e.g. maximum deviation of 5 kHz with a highest modulating frequency of 3 kHz is a Deviation Ratio of 1.66 ."
}
]
}
]
}
]
},
{
"content": "The deviation is dependent on the amplitude of the modulating frequency.",
"children": [
{
"content": "A-5-5-6 (C) In an FM transmitter system, the amount of deviation from the centre frequency is determined solely by the:\nA\tamplitude and the frequency of the modulating frequency\nB\tmodulating frequency and the amplitude of the centre frequency\nC\t**amplitude** of the modulating frequency\nD\tfrequency of the modulating frequency",
"children": [
{
"content": "> In Frequency Modulation, the amplitude of the modulation is translated into the importance of the deviation, the modulation frequency is reflected in the rhythm of the deviation."
}
]
}
]
},
{
"content": "FM produces sidebands",
"children": [
{
"content": "A-5-5-7 (A) Any FM wave with single-tone modulation has:\nA\tan **infinite** number of sideband frequencies\nB\ttwo sideband frequencies\nC\tfour sideband frequencies\nD\tone sideband frequency",
"children": [
{
"content": "> Unlike AM where a single modulating frequency creates only a pair of side frequencies (one on each side of the carrier), FM creates an infinite number of side frequency pairs; the Modulation Index influences the amplitude of the side frequencies through a mathematical relation known as a Bessel Function. The number of side frequencies with significant amplitude determines the required bandwidth. For certain Modulation Index values, there is zero energy at the centre frequency; the energy is then totally found in the side frequencies."
}
]
}
]
},
{
"content": "Counterintuitively, a **phase** modulator is used to achieve *frequency* modulation of a power amplifier.",
"children": [
{
"content": "A-5-6-5 (A) What type of circuit varies the tuning of an amplifier tank circuit to produce FM signals?\nA\tA **phase modulator**\nB\tA balanced modulator\nC\tA double balanced mixer\nD\tAn audio modulator",
"children": [
{
"content": "> Two methods exist to produce Frequency Modulation. The Direct Method supposes forcing deviation directly on the oscillator; deviation is then multiplied along with the oscillator frequency up to the operating frequency. Phase Modulation is an indirect method whereby the phase of the signal is affected (i.e., retarding/advancing) in step with the modulation by varying a reactance on a stage other than the oscillator."
}
]
}
]
},
{
"content": "emphasis and de-emphasis",
"children": [
{
"content": "A-6-4-1 (B) What audio shaping network is added at an FM receiver to restore proportionally attenuated lower audio frequencies?\nA\tA heterodyne suppressor\nB\tA de-emphasis network\nC\tA pre-emphasis network\nD\tAn audio prescaler",
"children": [
{
"content": "> With \"true\" FM, deviation is independent of modulating frequency, actual deviation is determined solely by the modulating amplitude. With Phase Modulation, deviation depends on the amount of phase shift and its rapidity, increasing modulating frequency results in proportionally more deviation even if amplitude is held constant. Because commercial standards were based on Phase Modulation, an FM transmitter requires an artificial boost in high frequency response so that PM and FM sound the same at the receiver. A pre-emphasis network tailors the frequency response in the FM transmitter. De-emphasis is employed in the receiver to restore a flat audio response."
}
]
}
]
},
{
"content": "FM bandwidth, deviation",
"children": [
{
"content": "A-5-5-10 (D) What is the significant bandwidth of an FM-phone transmission having a +/- 5-kHz deviation and a 3-kHz modulating frequency?\nA\t8 kHz\nB\t5 kHz\nC\t3 kHz\nD\t16 kHz",
"children": [
{
"content": "> Carson's Rule permits estimating the bandwidth of an FM signal: bandwidth equals twice the sum of deviation + modulating frequency, in this example, 5 + 3 = 8, twice 8 = 16. [ Mathematician and engineer John R. Carson (1887-1940) had predicted the approximate bandwidth of an FM signal circa 1922. ]"
}
]
},
{
"content": "A-5-5-11 (D) What is the frequency deviation for a 12.21-MHz reactance-modulated oscillator in a +/- 5-kHz deviation, 146.52-MHz FM-phone transmitter?\nA\t+/- 12 kHz\nB\t+/- 5 kHz\nC\t+/- 41.67 Hz\nD\t+/- 416.7 Hz",
"children": [
{
"content": "> In this example, the frequency multiplication ratio between oscillator and output is 12 ( 146.52 divided by 12.21 = 12 ). Hence, the oscillator needs only be shifted by 416.7 Hz, i.e., 5000 Hz divided by 12.\n\n' -- -- -- --"
}
]
}
]
},
{
"content": "Audio shaping called pre-emphasis is used on FM transmitters.",
"children": [
{
"content": "A-5-6-6 (A) What audio shaping network is added at an FM transmitter to attenuate the lower audio frequencies?\nA\tA **pre-emphasis network**\nB\tAn audio prescaler\nC\tA heterodyne suppressor\nD\tA de-emphasis network",
"children": [
{
"content": "> With direct FM, deviation is independent of modulating frequency, actual **deviation is determined solely by the modulating amplitude**."
},
{
"content": ">With Phase Modulation, deviation depends on the amount of phase shift and its rapidity, increasing modulating frequency results in proportionally more deviation even if amplitude is held constant. Because commercial standards were based on Phase Modulation, an FM transmitter requires an artificial boost in high frequency response so that PM and FM sound the same at the receiver. A pre-emphasis network tailors the frequency response in the FM transmitter. De-emphasis is employed in the receiver to restore a flat audio response."
}
]
},
{
"content": "A-5-6-8 (D) The characteristic difference between a phase modulator and a frequency modulator is:\nA\tthe centre frequency\nB\tde-emphasis\nC\tfrequency inversion\nD\t**pre-emphasis**",
"children": [
{
"content": "> With direct FM, deviation is independent of modulating frequency, actual deviation is determined solely by the modulating amplitude. With Phase Modulation, deviation depends on the amount of phase shift and its rapidity, increasing modulating frequency results in proportionally more deviation even if amplitude is held constant. Because commercial standards were based on Phase Modulation, an FM transmitter requires an artificial boost in high frequency response so that PM and FM sound the same at the receiver. A pre-emphasis network tailors the frequency response in the FM transmitter. De-emphasis is employed in the receiver to restore a flat audio response."
}
]
}
]
}
]
}
]
},
{
"content": "\n{L08} Receivers.",
"children": [
{
"content": "The simplest receiver consists of a tuned front-end and a detector. An example is a crystal receiver."
},
{
"content": "A **tuned-RF** receiver - old - cascaded amplifiers, all operating at the input RF frequency"
},
{
"content": "A **heterodyne** receiver (also called a **direct conversion** design) couples a local oscillator into the front end of a basic receiver; this allows unmodulated (continuous wave) carriers to be detected the their resulting AF beat tone.",
"children": [
{
"content": "All transmitters are now continuous wave; do spark-gap transmitters behave differently when received by crystal sets?"
},
{
"content": "The word \"heterodyne\" is an archaic 1920s marketing term involving the roots *hetero*, meaning different; and *dyne*, evoking automatic transformation. In this context, the word alludes to the two different frequencies present, and the mixed between them."
}
]
},
{
"content": "In this context, the oscillatoris called a beat frequency oscillator or BFO.",
"children": [
{
"content": "A-6-2-2 (A) A superheterodyne receiver designed for SSB reception must have a beat-frequency oscillator (BFO) because:\nA\tthe suppressed carrier must be replaced for detection\nB\tit phases out the unwanted sideband signal\nC\tit reduces the pass-band of the IF stages\nD\tit beats with the receiver carrier to produce the missing sideband",
"children": [
{
"content": "> The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to \"reinsert the carrier\" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain."
}
]
},
{
"content": "A-6-2-5 (B) The BFO is off-set slightly (500 - 1 500 Hz) from the incoming signal to the detector. This is required:\nA\tto protect the incoming signal from interference\nB\tto beat with the incoming signal\nC\tto pass the signal without interruption\nD\tto provide additional amplification",
"children": [
{
"content": "> The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to \"reinsert the carrier\" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain."
}
]
}
]
},
{
"content": "In this context, *direct* refers to the intelligence carried by the RF signal being converted directly from RF to AF."
},
{
"content": "The **super-heterodyne** uses a (tunable) (somewhat-selective) RF filter stage called a per-selector, the output of which is mixed with the output of a local oscillator, to down-convert to a lower frequency called the intermediate frequency. This is followed by an even more selective IF filter. "
},
{
"content": "A single-conversion superheterodyn incorporates a single IF stage; a double-conversion uses two IF stages.\n",
"children": [
{
"content": "The local oscillator mixes with the input frequency; the result must be near the IF frequency\n\n```\nf_LO +/- f_in = f_IF\n```"
},
{
"content": "For example:\n\n```\n16 +/- x = 9\n\nso\n\n-x = 16 - 9 = 7\n\nbut also \nx = 9 - 16 = -7\n\nor\n\nx = \n\nx = 16 - 9 = 7\n```",
"children": [
{
"content": "A-6-1-9 (A) A single conversion receiver with a 9 MHz IF has a local oscillator operating at 16 MHz. The frequency it is tuned to is:\n**A\t7 MHz**\nB\t16 MHz\nC\t21 MHz\nD\t9 MHz",
"children": [
{
"content": "> In a superheterodyne receiver, injection from the Local Oscillator can be above or below the operating frequency. There could be two answers: Local Oscillator minus Intermediate Frequency or Local Oscillator plus Intermediate Frequency."
}
]
}
]
}
]
},
{
"content": "[image rejection](https://www.electronics-notes.com/articles/radio/radio-receiver-selectivity/image-rejection-response.php)\n\nThe process of mixing the wideband input signal with the local oscillator, and accepting a given IF passband, results in the reception of **image signals**; which are due to the nature of the mixing transformation.\n\nA pre-selector is a passband filter in front of the RF amp that increases the empty gap between the IF band and the image band.\n\nThe location of the IF passband determines the location of the **image band**. Graphical methods are recommended here.",
"children": [
{
"content": "A-6-5-1 (C) What part of a superheterodyne receiver determines the image rejection ratio of the receiver?\nA\tAGC loop\nB\tIF filter\nC\tRF amplifier **pre-selector**\nD\tProduct detector",
"children": [
{
"content": "> The Image is the other frequency that can successfully mix with the Local Oscillator and produce an output out of the Mixer at the Intermediate frequency. Selectivity ahead of the Mixer must be employed to prevent that signal from reaching the Mixer."
}
]
},
{
"content": "A-6-5-6 (D) Which of the following is an important reason for using a VHF intermediate frequency in an HF receiver?\nA\tTo provide a greater tuning range\nB\tTo tune out cross-modulation distortion\nC\tTo prevent the generation of spurious mixer products\nD\tTo move the **image response** far away from the filter passband",
"children": [
{
"content": "> Whether injection from the Local Oscillator is above or below the operating frequency, the Image Frequency is always separated from the operating frequency by twice the Intermediate Frequency. A very high Intermediate Frequency moves the Image well out of the preselector bandpass."
}
]
}
]
},
{
"content": "double-conversion",
"children": [
{
"content": "The incorporate two cascaded IF stages, each fed by a dedicated local oscillator.",
"children": [
{
"content": "A-6-1-10 (D) A double conversion receiver designed for SSB reception has a beat frequency oscillator and:\nA\tone IF stage and one local oscillator\nB\ttwo IF stages and three local oscillators\nC\ttwo IF stages and one local oscillator\nD\t**two** IF stages and **two** local oscillators\n> Key words: DOUBLE CONVERSION. Double conversion entails two Mixers, two Local Oscillators and two Intermediate Frequency chains."
}
]
},
{
"content": "A-6-1-11 (B) The advantage of a double conversion receiver over a single conversion receiver is that it:\nA\tproduces a louder audio signal\nB\tsuffers less from **image interference** for a given front end sensitivity\nC\tdoes not drift off frequency\nD\tis a more sensitive receiver",
"children": [
{
"content": "> Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators."
}
]
},
{
"content": "The first IF stage is optimized for image rejection, and the second IF stage is optimized for selectivity. ",
"children": [
{
"content": "A-6-1-6 (C) In a dual-conversion superheterodyne receiver what are the respective aims of the first and second conversion:\nA\tselectivity and dynamic range\nB\timage rejection and noise figure\nC\timage rejection and selectivity\nD\tselectivity and image rejection",
"children": [
{
"content": "> The first conversion to a high IF places the image frequency far away from the operating frequency so it can be optimally rejected by the front-end filtering. The second conversion to a low IF performs the traditional function of ensuring selectivity to protect the receiver from adjacent channels."
}
]
}
]
},
{
"content": "Recall that mixing is a non-linear process, with many moving parts. With two mixing stages, the resulting mixing products may be all over the place, waiting to suck.",
"children": [
{
"content": "When it works, we call it mixing; when it does not work, we call it intermodulation."
},
{
"content": "A-6-1-5 (A) A multiple conversion superheterodyne receiver is more susceptible to spurious responses than a single-conversion receiver because of the:\nA\tadditional oscillators and mixing frequencies involved in the design\n~~B\tpoorer selectivity in the IF caused by the multitude of frequency changes\nC\tgreater sensitivity introducing higher levels of RF to the receiver\nD\tAGC being forced to work harder causing the stages concerned to overload~~",
"children": [
{
"content": "> Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators."
}
]
}
]
},
{
"content": "A-6-1-3 (D) One of the greatest advantages of the double-conversion over the single-conversion receiver is that it:\nA\tis much more stable\nB\tis much more sensitive\nC\tproduces a louder signal at the output\nD\tgreater reduction of image interference for a given front end selectivity",
"children": [
{
"content": "> Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators."
}
]
}
]
},
{
"content": "The front-end consists of an (optional) rf amplifier, and the first mixer",
"children": [
{
"content": "A-6-1-7 (B) Which stage of a receiver has its input and output circuits tuned to the received frequency?\nA\tThe detector\nB\tThe RF amplifier\nC\tThe local oscillator\nD\tThe audio frequency amplifier\n> Key word: TUNED. Of all the stages listed, only one runs at the operating frequency: the radio-frequency amplifier."
},
{
"content": "A-6-2-8 (C) In a superheterodyne receiver without an RF amplifier, the input to the mixer stage has a variable capacitor in parallel with an inductance. The variable capacitor is for:\nA\ttuning the beat-frequency oscillator\nB\ttuning both the antenna and the local oscillator\nC\ttuning the receiver preselector to the reception frequency\nD\ttuning both the antenna and the beat-frequency oscillator",
"children": [
{
"content": "> In the absence of a radio-frequency amplifier, the input to the Mixer must be an antenna tuning circuit."
}
]
},
{
"content": "A-6-2-10 (D) Which two stages in a superheterodyne receiver have input tuned circuits tuned to the same frequency?\nA\tIF and local oscillator\nB\tRF and IF\nC\tRF and local oscillator\nD\tRF and first mixer\n> Through an elimination process, only one answer makes sense. The input and the output of the radio-frequency amplifier run at the operating frequency. The output of the RF amplifier constitutes the input to the Mixer."
},
{
"content": "A-6-3-3 (A) How much gain should be used in the RF amplifier stage of a receiver?\nA\tSufficient gain to allow weak signals to overcome noise generated in the first mixer stage\nB\tAs much gain as possible, short of self-oscillation\nC\tIt depends on the amplification factor of the first IF stage\nD\tSufficient gain to keep weak signals below the noise of the first mixer stage",
"children": [
{
"content": "> The Radio-Frequency Amplifier should only introduce enough gain to override the internal noise of the subsequent Mixer. Too much gain will degrade Dynamic Range; Dynamic Range is broadly defined as a ratio between the strongest signals that can be tolerated near the passband and the \"Minimum Discernible Signal\"."
}
]
},
{
"content": "A-6-3-4 (B) What is the primary purpose of an RF amplifier in a receiver?\nA\tTo provide most of the receiver gain\nB\tTo improve the receiver noise figure\nC\tTo vary the receiver image rejection by using the AGC\nD\tTo develop the AGC voltage\n> The Intermediate Frequency chain is responsible for the selectivity and a large part of the gain. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver."
}
]
},
{
"content": "IF stage",
"children": [
{
"content": "A-6-3-2 (A) Which of the following is a purpose of the first IF amplifier stage in a receiver?\nA\tTo improve selectivity and gain\nB\tTo tune out cross-modulation distortion\nC\tTo increase dynamic response\nD\tTo improve noise figure performance",
"children": [
{
"content": "> The Intermediate Frequency chain is responsible for the selectivity and a large part of the gain. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver."
}
]
},
{
"content": "A-6-1-4 (A) In a communications receiver, a crystal filter would be located in the:\nA\tIF circuits\nB\tlocal oscillator\nC\taudio output stage\nD\tdetector",
"children": [
{
"content": "> The Intermediate Frequency chain is responsible for most of the selectivity. Crystal filters or mechanical filters can be used at the Intermediate Frequency. Digital Signal Processing (DSP) is used in modern receivers."
}
]
},
{
"content": "A-6-1-2 (C) What factors should be considered when selecting an intermediate frequency?\nA\tInterference to other services\nB\tCross-modulation distortion and interference\nC\tImage rejection and responses to unwanted signals\nD\tNoise figure and distortion",
"children": [
{
"content": "> Two frequencies, one above and one below the Local Oscillator frequency, can produce a mixing result at the Intermediate Frequency. The one resulting in the unwanted product is the Image Frequency. With a low Intermediate Frequency, selectivity and gain are easier to achieve but image rejection suffers. With a high Intermediate Frequency, image rejection is facilitated but selectivity is more difficult to achieve. A Double-conversion receiver deals with image rejection with an initial conversion and restores selectivity with a subsequent down-conversion. Two conversions, however, expose the designer to twice the risk of spurious responses due to spurious oscillations in local oscillators."
}
]
},
{
"content": "A-6-2-4 (C) If the incoming signal to the mixer is 3 600 kHz and the first IF is 9 MHz, at which one of the following frequencies would the local oscillator (LO) operate?\nA\t10 600 kHz\nB\t21 600 kHz\nC\t5 400 kHz\nD\t3 400 kHz",
"children": [
{
"content": "> In a superheterodyne receiver, injection from the Local Oscillator can be above or below the operating frequency. There could be two answers: Intermediate Frequency plus operating frequency or Intermediate Frequency minus operating frequency."
}
]
},
{
"content": "A-6-2-3 (D) The first mixer in the receiver mixes the incoming signal with the local oscillator to produce:\nA\tan audio frequency\nB\ta radio frequency\nC\ta high frequency oscillator (HFO) frequency\nD\tan intermediate frequency",
"children": [
{
"content": "> The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain."
}
]
}
]
},
{
"content": "mixer",
"children": [
{
"content": "A-6-2-9 (A) What receiver stage combines a 14.25-MHz input signal with a 13.795-MHz oscillator signal to produce a 455-kHz intermediate frequency (IF) signal?\nA\tMixer\nB\tBFO\nC\tVFO\nD\tMultiplier",
"children": [
{
"content": "> The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain."
}
]
},
{
"content": "A-6-2-11 (C) The mixer stage of a superheterodyne receiver:\nA\tacts as a buffer stage\nB\tdemodulates SSB signals\nC\tproduces an intermediate frequency\nD\tproduces spurious signals",
"children": [
{
"content": "> The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain."
}
]
}
]
},
{
"content": "Local oscillator",
"children": [
{
"content": "A-6-2-7 (C) In a superheterodyne receiver, a stage before the IF amplifier has a variable capacitor in parallel with a trimmer capacitor and an inductance. The variable capacitor is for:\nA\ttuning of the beat-frequency oscillator (BFO)\nB\ttuning both the antenna and the LO\nC\ttuning of the local oscillator (LO)\nD\ttuning both the antenna and the BFO",
"children": [
{
"content": "> Two stages may require tuning ahead of the Intermediate Frequency amplifier: the preselector and the high-frequency oscillator, commonly known as the Local Oscillator. As the question alludes to one trimmer and one inductance, only one circuit can be tuned."
}
]
},
{
"content": "A-6-2-6 (D) It is very important that the oscillators contained in a superheterodyne receiver are:\nA\tsensitive and selective\nB\tstable and sensitive\nC\tselective and spectrally pure\nD\tstable and spectrally pure",
"children": [
{
"content": "> Oscillators need to be free of drift regardless of voltage and temperature variations or mechanical vibrations. Spectral purity is the absence of harmonics, other spurious oscillations or noise; purity limits spurious responses in the subsequent mixing processes."
}
]
}
]
},
{
"content": "superhet",
"children": [
{
"content": "A-6-2-1 (A) The mixer stage of a superheterodyne receiver is used to:\nA\tchange the frequency of the incoming signal to that of the IF\nB\tallow a number of IF frequencies to be used\nC\tremove image signals from the receiver\nD\tproduce an audio frequency for the speaker",
"children": [
{
"content": "> The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain."
}
]
},
{
"content": "A-6-1-8 (B) Which stage of a superheterodyne receiver lies between a tuneable stage and a fixed tuned stage?\nA\tLocal oscillator\nB\tMixer\nC\tRadio frequency amplifier\nD\tIntermediate frequency amplifier\n> The superheterodyne concept is based on converting the operating frequency to a fixed Intermediate Frequency: the Mixer performs that function by combining the output of the tuneable RF amplifier with the Local Oscillator signal to feed the fixed-tuned Intermediate Frequency chain."
},
{
"content": "A-6-1-1 (C) What are the advantages of the frequency conversion process in a superheterodyne receiver?\nA\tAutomatic soft-limiting and automatic squelching\nB\tAutomatic squelching and increased sensitivity\nC\tIncreased selectivity and optimal tuned circuit design\nD\tAutomatic detection in the RF amplifier and increased sensitivity",
"children": [
{
"content": "> Down-converting the operating frequency to a lower Intermediate Frequency facilitates selectivity: for example, 0.6% of 455 kilohertz is 2.7 kHz, 0.6% of 3.7 megahertz is 22 kHz."
}
]
}
]
},
{
"content": "noise floor",
"children": [
{
"content": "A-6-3-1 (A) What is meant by the noise floor of a receiver?\nA\tThe weakest signal that can be detected above the receiver internal noise\nB\tThe weakest signal that can be detected under noisy atmospheric conditions\nC\tThe minimum level of noise that will overload the receiver RF amplifier stage\nD\tThe amount of noise generated by the receiver local oscillator\n> A receiver's \"Noise Floor\" is the power level at which an incoming signal exhibits a Signal-To-Noise ratio of zero decibel: that is, the signal power equals the internal noise power level. Noise Floor is evaluated while measuring \"Minimum Discernible Signal (MDS)\". The \"Noise Figure\" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver."
},
{
"content": "A-6-3-7 (A) The lower the receiver noise figure becomes, the greater will be the receiver's _________:\nA\tsensitivity\nB\trejection of unwanted signals\nC\tselectivity\nD\tstability\n> The \"Noise Figure\" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver."
},
{
"content": "A-6-3-8 (D) The noise generated in a receiver of good design originates in the:\nA\tdetector and AF amplifier\nB\tBFO and detector\nC\tIF amplifier and detector\nD\tRF amplifier and mixer\n> The \"Noise Figure\" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver."
},
{
"content": "A-6-3-9 (C) Why are very low noise figures relatively unimportant for a high frequency receiver?\nA\tThe use of SSB and CW on the HF bands overcomes the noise\nB\tRegardless of the front end, the succeeding stages when used on HF are very noisy\nC\tExternal HF noise, man-made and natural, are higher than the internal noise generated by the receiver\nD\tIonospheric distortion of the received signal creates high noise levels\n> Below 30 megahertz, the antenna picks-up atmospheric noise and man-made noise at levels far more important than internal noise. As the frequency of operation rises, those types of noise become less prevalent. On Ultra High Frequencies (UHF) and above, the internal noise becomes the limiting factor in receiving weak signals. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver: for weak signal work on 2 metres and up, more attention must be placed on reducing internal noise in the front-end."
}
]
},
{
"content": "dynamic range",
"children": [
{
"content": "A-6-3-6 (C) What is the term used for the decibel difference (or ratio) between the largest tolerable receiver input signal (without causing audible distortion products) and the minimum discernible signal (sensitivity)?\nA\tStability\nB\tNoise figure\nC\tDynamic range\nD\tDesign parameter\n> Dynamic Range is broadly defined as a ratio between the strongest signals that can be tolerated near the passband and the \"Minimum Discernible Signal\". The \"Noise Figure\" of a receiver is a comparison of Signal-to-Noise ratio at the input and Signal-to-Noise ratio at the output; it assesses the degradation in Signal-to-Noise ratio caused by added noise. A low Noise Figure suggests that little noise was added internally and is a hallmark of sensitivity. The front-end of the receiver, where signals are weakest, is responsible for the noise performance of a receiver."
},
{
"content": "A-6-3-10 (B) The term which relates specifically to the amplitude levels of multiple signals that can be accommodated during reception is called:\nA\tnoise figure\nB\tdynamic range\nC\tAGC\nD\tcross-modulation index\n> Dynamic Range is broadly defined as a ratio between the strongest signals that can be tolerated near the passband and the \"Minimum Discernible Signal\". Other related notions include Blocking Dynamic Range and Intermodulation Dynamic Range. Blocking Dynamic Range measures how much of a single strong off-channel signal can be tolerated while receiving a weak signal, it is a measure of desensitization or immunity to overload. Intermodulation Dynamic Range verifies how strong two off-channel signals can be without spurious responses being generated in the receiver, it is a measure of resistance to intermodulation."
},
{
"content": "A-6-5-10 (B) Poor dynamic range of a receiver can cause many problems when a strong signal appears within or near the front-end bandpass. Which of the following is NOT caused as a direct result?\nA\tCross-modulation\nB\tFeedback\nC\tDesensitization\nD\tIntermodulation\n> Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses."
}
]
},
{
"content": "selectivity",
"children": [
{
"content": "A-6-3-11 (B) Normally, front-end selectivity is provided by the resonant networks both before and after the RF stage in a superheterodyne receiver. This whole section of the receiver is often referred to as the:\nA\tpass-selector\nB\tpreselector\nC\tpreamble\nD\tpreamplifier\n> A preselector is a tuned stage which passes a desired range of signals to a receiver: it ensures a certain preliminary selection. It may or may not be amplified; in other words, active or passive."
}
]
},
{
"content": "product detector",
"children": [
{
"content": "A-6-4-2 (C) What does a product detector do?\nA\tIt amplifies and narrows band-pass frequencies\nB\tIt detects cross-modulation products\nC\tIt mixes an incoming signal with a locally generated carrier\nD\tIt provides local oscillations for input to a mixer\n> The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to \"reinsert the carrier\" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain."
}
]
},
{
"content": "distortion",
"children": [
{
"content": "A-6-4-3 (B) Distortion in a receiver that only affects strong signals usually indicates a defect in or mis-adjustment of the:\nA\tRF amplifier\nB\tautomatic gain control (AGC)\nC\tIF amplifier\nD\tAF amplifier\n> \"Distortion that affects only strong signals is the normal symptom of AGC (Automatic Gain Control) failure.\" (ARRL Handbook 1985)"
}
]
},
{
"content": "AGC",
"children": [
{
"content": "A-6-4-4 (C) In a superheterodyne receiver with automatic gain control (AGC), as the strength of the signal increases, the AGC:\nA\tdistorts the signal\nB\tintroduces limiting\nC\treduces the receiver gain\nD\tincreases the receiver gain\n> The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be \"IF-derived\", some say \"RF-Derived\" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or \"AF-derived\" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier."
},
{
"content": "A-6-4-7 (B) The overall output of an AM/CW/SSB receiver can be adjusted by means of manual controls on the receiver or by use of a circuit known as:\nA\tautomatic load control\nB\tautomatic gain control\nC\tautomatic frequency control\nD\tinverse gain control\n> The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be \"IF-derived\", some say \"RF-Derived\" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or \"AF-derived\" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier."
},
{
"content": "A-6-4-8 (A) AGC voltage is applied to the:\nA\tRF and IF amplifiers\nB\tAF and IF amplifiers\nC\tRF and AF amplifiers\nD\tdetector and AF amplifiers\n> The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be \"IF-derived\", some say \"RF-Derived\" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or \"AF-derived\" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier."
},
{
"content": "A-6-4-9 (C) AGC is derived in a receiver from one of two circuits. Depending on the method used, it is called:\nA\tIF derived or RF derived\nB\tdetector derived or audio derived\nC\tIF derived or audio derived\nD\tRF derived or audio derived\n> The AGC (Automatic Gain Control) circuit reduces receiver gain as signal strength increases. AGC can be \"IF-derived\", some say \"RF-Derived\" (a slight misnomer), by sampling the output of the last Intermediate Frequency stage or \"AF-derived\" by sampling the output of the detector. The resulting control voltage is applied to the Intermediate Frequency amplifiers and, sometimes, Radio-Frequency amplifier."
},
{
"content": "A-6-4-10 (D) Which two variables primarily determine the behaviour of an automatic gain control (AGC) loop?\nA\tBlanking level and slope\nB\tSlope and bandwidth\nC\tClipping level and hang time\nD\tThreshold and decay time\n> The AGC threshold is the level in the monitored circuit at which the AGC circuit begins to reduce gain. The AGC decay time determines how quickly gain is restored once the strong signal disappears."
}
]
},
{
"content": "detector",
"children": [
{
"content": "A-6-4-5 (B) The amplified IF signal is applied to the ____________ stage in a superheterodyne receiver:\nA\tLO\nB\tdetector\nC\tRF amplifier\nD\taudio output\n> Remember your Basic Qualification? The Detector follows the Intermediate Frequency amplifier."
},
{
"content": "A-6-4-6 (C) The low-level output of a detector is:\nA\tfed directly to the speaker\nB\tapplied to the RF amplifier\nC\tapplied to the AF amplifier\nD\tgrounded via the chassis\n> Remember your Basic Qualification? The Audio Amplifier follows the Detector."
},
{
"content": "A-6-4-11 (B) What circuit combines signals from an IF amplifier stage and a beat-frequency oscillator (BFO), to produce an audio signal?\nA\tA VFO circuit\nB\tA product detector circuit\nC\tAn AGC circuit\nD\tA power supply circuit\n> The Beat Frequency Oscillator feeds the Product Detector for CW and SSB detection. Mixing the Intermediate Frequency with the BFO signal in the Product Detector produces an audio output. In Single Sideband, it is said to \"reinsert the carrier\" as it recreates a reference at the exact frequency at which the carrier, suppressed at the transmitter, would have appeared out of the Intermediate Frequency chain."
}
]
},
{
"content": "desensitization",
"children": [
{
"content": "A-6-5-2 (A) What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency?\nA\tDesensitization\nB\tCross-modulation interference\nC\tSquelch gain rollback\nD\tQuieting\n> Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses."
},
{
"content": "A-6-5-3 (D) What causes receiver desensitization?\nA\tSquelch gain adjusted too high\nB\tSquelch gain adjusted too low\nC\tAudio gain adjusted too low\nD\tStrong near frequency signals\n> Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses."
},
{
"content": "A-6-5-4 (B) What is one way receiver desensitization can be reduced?\nA\tIncrease the transmitter audio gain\nB\tUse a cavity filter\nC\tDecrease the receiver squelch gain\nD\tIncrease the receiver bandwidth\n> Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses."
}
]
},
{
"content": "intermodulation",
"children": [
{
"content": "A-6-5-5 (A) What causes intermodulation in an electronic circuit?\nA\tNonlinear circuits or devices\nB\tToo little gain\nC\tPositive feedback\nD\tLack of neutralization\n> Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses."
},
{
"content": "A-6-5-7 (B) Intermodulation interference is produced by:\nA\tthe mixing of more than one signal in the first or second intermediate frequency amplifiers of a receiver\nB\tthe mixing of two or more signals in the front-end of a superheterodyne receiver\nC\tthe interaction of products from high-powered transmitters in the area\nD\tthe high-voltage stages in the final amplifier of an amplitude or frequency-modulated transmitter\n> Desensitization is a symptom of front-end overload where a strong adjacent off-channel signal provokes a drop in receiver sensitivity. The only cure for desensitization is to keep the offending signal out of the receiver. Other manifestations of front-end overload are intermodulation and cross-modulation where strong signals push the RF amplifier or Mixer into non-linear operation resulting in spurious responses."
},
{
"content": "A-6-5-11 (B) Which of these measurements is a good indicator of VHF receiver performance in an environment of strong out-of-band signals?\nA\tIntermediate frequency rejection ratio\nB\tTwo-tone Third-Order IMD Dynamic Range, 10 MHz spacing\nC\tThird-Order Intercept Point\nD\tBlocking Dynamic Range",
"children": [
{
"content": "> \"The FM Two-tone, third-order dynamic range, 10-MHz offset ... is a wide-band dynamic-range test on VHF equipment, using two strong signals just outside the amateur band (usually the abode of nearby pager transmitters). (...) This test is a good indicator of relative IMD performance\". (RFI - Intermodulation, ARRL, Ed Hare, W1RFI)"
}
]
}
]
},
{
"content": "frequency stability",
"children": [
{
"content": "A-6-5-8 (A) Which of the following is NOT a direct cause of instability in a receiver?\nA\tDial display accuracy\nB\tMechanical rigidity\nC\tFeedback components\nD\tTemperature variations\n> Key words: NOT A DIRECT CAUSE. Temperature variations, voltage variations and movements due to mechanical stresses will cause changes in frequency. The selection of feedback components, notably their temperature coefficient, is paramount for stability. Dial accuracy is not instability per se."
},
{
"content": "A-6-5-9 (B) Poor frequency stability in a receiver usually originates in the:\nA\tmixer\nB\tlocal oscillator and power supply\nC\tdetector\nD\tRF amplifier\n> Stability is the ability to stay on frequency despite other variations. The Local Oscillator indirectly sets the operating frequency. Temperature variations, voltage variations and movements due to mechanical stresses will cause changes in frequency."
}
]
}
]
},
{
"content": "\n{L13} Digital Signal Processing.",
"children": [
{
"content": "Digital Signal Processors consist of an analog to digital converter, a mathematical transform, a digital to analog converter and a low pass filter.",
"children": [
{
"content": "A-5-7-6 (D) What do you call the circuit which employs an analog to digital converter, a mathematical transform, a digital to analog converter and a low pass filter?\nA\tDigital formatter\nB\tMathematical transformer\nC\tDigital transformer\nD\tDigital signal processor",
"children": [
{
"content": "> Digital Signal Processing first transforms an analog signal to digital via an analog-to-digital converter (ADC), performs mathematical operations to filter or demodulate, for example, and recreates an analog signal through a digital-to-analog converter (DAC). Aliasing is a situation where input frequencies above the sampling rate get erroneously reproduced as lower frequencies; the situation is prevented through the use of an anti-aliasing filter (a low-pass filter)."
}
]
}
]
},
{
"content": "There is no such thing as an aliasing amplifier.",
"children": [
{
"content": "A-5-7-3 (B) Which of the following functions is not included in a typical digital signal processor?\nA\tMathematical transform\nB\t**Aliasing amplifier**\nC\tAnalog to digital converter\nD\tDigital to analog converter",
"children": [
{
"content": "> Digital Signal Processing first transforms an analog signal to digital via an analog-to-digital converter (ADC), performs mathematical operations to filter or demodulate, for example, and recreates an analog signal through a digital-to-analog converter (DAC). Aliasing is a situation where input frequencies above the sampling rate get erroneously reproduced as lower frequencies; the situation is prevented through the use of an anti-aliasing filter (a low-pass filter)."
}
]
}
]
},
{
"content": "In a DAC or ADC, 8 bits gives you **2^8 = 256** levels.",
"children": [
{
"content": "A-5-7-4 (D) How many bits are required to provide 256 discrete levels, or a ratio of 256:1?\nA\t6 bits\nB\t16 bits\nC\t4 bits\nD\t8 bits",
"children": [
{
"content": "> 256 levels in binary data spans the range 0 to 255. Add the value of each bit in an 8-bit binary number, starting with the lowest: 1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255."
}
]
}
]
},
{
"content": "Adding a bit doubles the range; which, for **amplitudes**, is [equivalent to 6 dB](https://en.wikipedia.org/wiki/Decibel).",
"children": [
{
"content": "A-5-7-5 (D) Adding one bit to the word length, is equivalent to adding ____ dB to the dynamic range of the digitizer:\nA\t1 dB\nB\t4 dB\nC\t3 dB\nD\t6 dB",
"children": [
{
"content": "> The number of bits determines the maximum number of distinct values available to represent a signal. For each sample, the analog-to-digital converter selects the closest value to describe the instantaneous value of the input signal. The difference between the real value and its numerical representation is a quantization error: plus or minus half a bit, i.e., 1 bit total. In digital terms, Signal-to-Noise Ratio and Dynamic Range are synonyms specifying the ratio between the largest possible sample value to the quantization error. Dynamic Range for fixed-point processors can be approximated by the data word size: 6 dB times number of bits. Each bit doubles the value, doubling voltage is 6 dB."
}
]
}
]
}
]
},
{
"content": "\n{L06} Basic Digital Techniques.",
"children": [
{
"content": "An OR Gate gives you a 1 when any of the inputs are 1.",
"children": [
{
"content": "A-2-10-2 (C) What is an OR gate?\nA\tA circuit that produces logic \"1\" at its output if all inputs are logic \"0\"\nB\tA circuit that produces a logic \"0\" at its output if any input is logic \"1\"\nC\tA circuit that produces a logic \"1\" at its output if any input is logic \"1\"\nD\tA circuit that produces a logic \"0\" at its output if all inputs are logic \"1\"",
"children": [
{
"content": "> Logic circuitry uses three main operations: \"AND\", \"OR\" and \"NOT\". The \"NOT\" is also called negation, complement or inversion. AND: true if both inputs are true. NAND: AND followed by a NOT, false when both inputs are true (AND, NAND: all inputs have a desired state). OR: true if either input is true. NOR: OR followed by a NOT, false if either input is true (OR,NOR: at least one input has desired state). XOR: true if both inputs are complementary. XNOR: XOR followed by a NOT, false if both inputs are complementary (XOR,XNOR: only one input has a desired state)."
}
]
}
]
},
{
"content": "A NOR gate is an OR gate with the output reversed. You get a zero if any of the inputs are 1.",
"children": [
{
"content": "A-2-10-3 (B) What is a NOR gate?\nA\tA circuit that produces a logic \"1\" at its output if some but not all of its inputs are logic \"1\"\nB\tA circuit that produces a logic \"0\" at its output if any or all inputs are logic \"1\"\nC\tA circuit that produces a logic \"0\" at its output only if all inputs are logic \"0\"\nD\tA circuit that produces a logic \"1\" at its output only if all inputs are logic \"1\"",
"children": [
{
"content": "> Logic circuitry uses three main operations: \"AND\", \"OR\" and \"NOT\". The \"NOT\" is also called negation, complement or inversion. AND: true if both inputs are true. NAND: AND followed by a NOT, false when both inputs are true (AND, NAND: all inputs have a desired state). OR: true if either input is true. NOR: OR followed by a NOT, false if either input is true (OR,NOR: at least one input has desired state). XOR: true if both inputs are complementary. XNOR: XOR followed by a NOT, false if both inputs are complementary (XOR,XNOR: only one input has a desired state)."
}
]
}
]
},
{
"content": "An exclusive OR (XOR) gate gives you a 1 if one (*and only one*) input is 1.",
"children": [
{
"content": "A-2-10-5 (C) What is an EXCLUSIVE OR gate?\nA\tA circuit that produces a logic \"1\" at its output when all of the inputs are logic \"1\"\nB\tA circuit that produces a logic \"1\" at its output when all of the inputs are logic \"0\"\nC\tA circuit that produces a logic \"1\" at its output when only one of the inputs is logic \"1\"\nD\tA circuit that produces a logic \"0\" at its output when only one of the inputs is logic \"1\"",
"children": [
{
"content": "> Logic circuitry uses three main operations: \"AND\", \"OR\" and \"NOT\". The \"NOT\" is also called negation, complement or inversion. AND: true if both inputs are true. NAND: AND followed by a NOT, false when both inputs are true (AND, NAND: all inputs have a desired state). OR: true if either input is true. NOR: OR followed by a NOT, false if either input is true (OR,NOR: at least one input has desired state). XOR: true if both inputs are complementary. XNOR: XOR followed by a NOT, false if both inputs are complementary (XOR,XNOR: only one input has a desired state)."
}
]
}
]
},
{
"content": "An exclusive NOR gate is an XOR in reverse.",
"children": [
{
"content": "A-2-10-6 (D) What is an EXCLUSIVE NOR gate?\nA\tA circuit that produces a logic \"1\" at its output when only one of the inputs is logic \"0\"\nB\tA circuit that produces a logic \"1\" at its output when only one of the inputs are logic \"1\"\nC\tA circuit that produces a logic \"0\" at its output when all of the inputs are logic \"1\"\nD\tA circuit that produces a logic \"1\" at its output when all of the inputs are logic \"1\"",
"children": [
{
"content": "> Logic circuitry uses three main operations: \"AND\", \"OR\" and \"NOT\". The \"NOT\" is also called negation, complement or inversion. AND: true if both inputs are true. NAND: AND followed by a NOT, false when both inputs are true (AND, NAND: all inputs have a desired state). OR: true if either input is true. NOR: OR followed by a NOT, false if either input is true (OR,NOR: at least one input has desired state). XOR: true if both inputs are complementary. XNOR: XOR followed by a NOT, false if both inputs are complementary (XOR,XNOR: only one input has a desired state)."
}
]
}
]
},
{
"content": "A NAND gate is an AND gate, witht he output reversed. You only get a 1 when the inputs are all zero.",
"children": [
{
"content": "A-2-10-1 (D) What is a NAND gate?\nA\tA circuit that produces a logic \"1\" at its output only when all inputs are logic \"1\"\nB\tA circuit that produces a logic \"0\" at its output if some but not all of its inputs are logic \"1\"\nC\tA circuit that produces a logic \"0\" at its output only when all inputs are logic \"0\"\nD\tA circuit that produces a logic \"0\" at its output only when all inputs are logic \"1\"",
"children": [
{
"content": "> Logic circuitry uses three main operations: \"AND\", \"OR\" and \"NOT\". The \"NOT\" is also called negation, complement or inversion. AND: true if both inputs are true. NAND: AND followed by a NOT, false when both inputs are true (AND, NAND: all inputs have a desired state). OR: true if either input is true. NOR: OR followed by a NOT, false if either input is true (OR,NOR: at least one input has desired state). XOR: true if both inputs are complementary. XNOR: XOR followed by a NOT, false if both inputs are complementary (XOR,XNOR: only one input has a desired state)."
}
]
}
]
},
{
"content": "An AND gate gives you a one only if all the inputs are 1.",
"children": [
{
"content": "A-2-10-7 (C) What is an AND gate?\nA\tA circuit that produces a logic \"1\" at its output only if one of its inputs is logic \"1\"\nB\tA circuit that produces a logic \"1\" at its output if all inputs are logic \"0\"\nC\tA circuit that produces a logic \"1\" at its output only if all its inputs are logic \"1\"\nD\tA circuit that produces a logic \"1\" at the output if at least one input is a logic \"0\"",
"children": [
{
"content": "> Logic circuitry uses three main operations: \"AND\", \"OR\" and \"NOT\". The \"NOT\" is also called negation, complement or inversion. AND: true if both inputs are true. NAND: AND followed by a NOT, false when both inputs are true (AND, NAND: all inputs have a desired state). OR: true if either input is true. NOR: OR followed by a NOT, false if either input is true (OR,NOR: at least one input has desired state). XOR: true if both inputs are complementary. XNOR: XOR followed by a NOT, false if both inputs are complementary (XOR,XNOR: only one input has a desired state)."
}
]
}
]
},
{
"content": "A NOT gate inverts the input.",
"children": [
{
"content": "A-2-10-4 (A) What is a NOT gate (also known as an INVERTER)?\nA\tA circuit that produces a logic \"0\" at its output when the input is logic \"1\"\nB\tA circuit that does not allow data transmission when its input is high\nC\tA circuit that allows data transmission only when its input is high\nD\tA circuit that produces a logic \"1\" at its output when the input is logic \"1\"",
"children": [
{
"content": "> Logic circuitry uses three main operations: \"AND\", \"OR\" and \"NOT\". The \"NOT\" is also called negation, complement or inversion. AND: true if both inputs are true. NAND: AND followed by a NOT, false when both inputs are true (AND, NAND: all inputs have a desired state). OR: true if either input is true. NOR: OR followed by a NOT, false if either input is true (OR,NOR: at least one input has desired state). XOR: true if both inputs are complementary. XNOR: XOR followed by a NOT, false if both inputs are complementary (XOR,XNOR: only one input has a desired state)."
}
]
}
]
},
{
"content": "A flip-flop is a **sequential** logic element with **two** output states. They are also called bistable multivibrators, or latches.",
"children": [
{
"content": "A-2-10-8 (B) What is a flip-flop circuit?\nA\tA binary sequential logic element with one stable state\nB\tA binary sequential logic element with two stable states\nC\tA binary sequential logic element with eight stable states\nD\tA binary sequential logic element with four stable states",
"children": [
{
"content": "> The \"flip-flop\" is a bistable multivibrator. The adjective \"bistable\" alludes to two possible stable states, set or reset. The circuit remains in one of the two states until a change is triggered. The terms \"flip-flop\" and \"latch\" are sometimes used interchangeably. Simple logic gates implement Combinational Logic: the output is determined only by the current inputs. In Sequential Logic, the output depends on current inputs and the exact sequence of prior events. [Nowadays, purists will tell you that a latch follows the input levels (transparency) before a final value is locked-in; a flip-flop captures data strictly on a clock transition (edge-triggered).]"
}
]
},
{
"content": "A-2-10-9 (A) What is a bistable multivibrator?\nA\tA flip-flop\nB\tAn OR gate\nC\tAn AND gate\nD\tA clock",
"children": [
{
"content": "> The \"flip-flop\" is a bistable multivibrator. The adjective \"bistable\" alludes to two possible stable states, set or reset. The circuit remains in one of the two states until a change is triggered. The terms \"flip-flop\" and \"latch\" are sometimes used interchangeably. Simple logic gates implement Combinational Logic: the output is determined only by the current inputs. In Sequential Logic, the output depends on current inputs and the exact sequence of prior events. [ Nowadays, purists will tell you that a latch follows the input levels (transparency) before a final value is locked-in; a flip-flop captures data strictly on a clock transition (edge-triggered). ]"
}
]
},
{
"content": "A-2-10-10 (D) What type of digital logic is also known as a latch?\nA\tA decade counter\nB\tAn OR gate\nC\tAn op-amp\nD\tA flip-flop",
"children": [
{
"content": "> The \"flip-flop\" is a bistable multivibrator. The adjective \"bistable\" alludes to two possible stable states, set or reset. The circuit remains in one of the two states until a change is triggered. The terms \"flip-flop\" and \"latch\" are sometimes used interchangeably. Simple logic gates implement Combinational Logic: the output is determined only by the current inputs. In Sequential Logic, the output depends on current inputs and the exact sequence of prior events. [ Nowadays, purists will tell you that a latch follows the input levels (transparency) before a final value is locked-in; a flip-flop captures data strictly on a clock transition (edge-triggered). ]"
}
]
}
]
},
{
"content": "They consist of two transistors wired together. When one of them is in conduction, the other is in cutoff.",
"children": [
{
"content": "A-2-10-11 (D) In a multivibrator circuit, when one transistor conducts, the other is:\nA\tsaturated\nB\treverse-biased\nC\tforward-biased\nD\tcut off\n> The transistors in a multivibrator circuit alternate between two states: conduction and cut-off. The Astable multivibrator can be used as a square-wave generator. The Monostable multivibrator assumes the alternate state for a given period when triggered. The Bistable multivibrator is used in latch and flip-flop circuits."
}
]
}
]
},
{
"content": "\n{L10} Digital Transmission Techniques.",
"children": [
{
"content": "This topic consists mostly of arbitrary trivia."
},
{
"content": "**Baudot and ASCII**",
"children": [
{
"content": "ASCII included lower case. Baudot does not.",
"children": [
{
"content": "A-5-8-4 (A) What is one advantage of using ASCII rather than Baudot code?\nA\tIt includes both upper and lower case text characters in the code\nB\tASCII includes built-in error correction\nC\tASCII characters contain fewer information bits\nD\tThe larger character set allows store-and-forward\n> With 5 bits, Baudot can accommodate 32 combinations ( 2 exponent 5 ) per character set; one set represents uppercase letters A through Z, the other are figures 0 through 9 plus other symbols. The original ASCII (American Standard Code for Information Interchange) used seven bits to accommodate 128 combinations; enough for lowercase and uppercase letters, all digits and other symbols. So called \"extended ASCII\" uses 8 bits for a total of 256 combinations, this adds accented letters."
}
]
},
{
"content": "ASCII uses 8 bits.",
"children": [
{
"content": "A-5-8-11 (A) How many information bits are included in the ISO-8859 extension to the ASCII code?\nA\t8\nB\t7\nC\t6\nD\t5\n> With 5 bits, Baudot can accommodate 32 combinations ( 2 exponent 5 ) per character set; one set represents uppercase letters A through Z, the other are figures 0 through 9 plus other symbols. The original ASCII (American Standard Code for Information Interchange) used seven bits to accommodate 128 combinations; enough for lowercase and uppercase letters, all digits and other symbols. So called \"extended ASCII\" uses 8 bits for a total of 256 combinations, this adds accented letters."
}
]
},
{
"content": "Baudot code uses five bits",
"children": [
{
"content": "A-5-8-10 (A) How many information bits are included in the Baudot code?\nA\t5\nB\t7\nC\t8\nD\t6\n> With 5 bits, Baudot can accommodate 32 combinations ( 2 exponent 5 ) per character set; one set represents uppercase letters A through Z, the other are figures 0 through 9 plus other symbols. The original ASCII (American Standard Code for Information Interchange) used seven bits to accommodate 128 combinations; enough for lowercase and uppercase letters, all digits and other symbols. So called \"extended ASCII\" uses 8 bits for a total of 256 combinations, this adds accented letters."
}
]
}
]
},
{
"content": "As per the name, [varicode](https://en.wikipedia.org/wiki/Varicode) consists of elements having unequal (variable) length.",
"children": [
{
"content": "A-5-8-1 (C) What digital code consists of elements having unequal length?\nA\tBaudot\nB\tASCII\nC\tVaricode\nD\tAX.25",
"children": [
{
"content": "> Varicode is an encoding method where ASCII characters are represented by bit patterns ranging from 1 to 10 bits in length. Varicode is used for PSK31 (\"Phase Shift Keying, 31 Baud\"). ASCII (American Standard Code for Information Interchange) or Baudot (RTTY) rely on a precise number of evenly-timed bits. AX.25 is a protocol used for packet transmission."
}
]
}
]
},
{
"content": "The OSI model : the base layer is the physical layer.",
"children": [
{
"content": "A-5-8-2 (A) Open Systems Interconnection (OSI) model standardizes communications functions as layers within a data communications system. Amateur digital radio systems often follow the OSI model in structure. What is the base layer of the OSI model involving the interconnection of a packet radio TNC to a computer terminal?\nA\tThe physical layer\nB\tThe link layer\nC\tThe network layer\nD\tThe transport layer",
"children": [
{
"content": "> Key words: TNC to COMPUTER INTERCONNECTION. Physical layer (for example, RS-232): the electrical, mechanical, procedural and functional specifications for moving data across a physical medium, including modulation, establishing and terminating connections. The Data Link layer packages data bits into frames, provides error-free transfer of frames including physical addressing, network topology, error notification. The Network layer (for example, Internetwork Protocol) uses logical addresses to route frames through a network of links. The Transport layer (for example, TCP Transmission Control Protocol) provides the end-to-end control, ensures that data is complete and properly sequenced ( e.g., retransmissions )."
}
]
}
]
},
{
"content": "A CRC is an error checking code.",
"children": [
{
"content": "A-5-8-3 (D) What is the purpose of a Cyclic Redundancy Check (CRC)?\nA\tLossy compression\nB\tError correction\nC\tLossless compression\nD\tError detection",
"children": [
{
"content": "> \"A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data\" (Wikipedia). A CRC is computed at the originating end and sent with the message; the receiving end does the same calculation, a mismatch in the CRC indicates that the payload was damaged. The CRC manages error detection, other mechanisms can provide error correction."
}
]
}
]
},
{
"content": "AMTOR ARQ - automatic repeat request",
"children": [
{
"content": "A-5-8-5 (A) What type of error control system is used in AMTOR ARQ (Mode A)?\nA\tThe receiving station automatically requests repeats when needed\nB\tThe receiving station checks the frame check sequence (FCS) against the transmitted FCS\nC\tEach character is sent twice\nD\tMode A AMTOR does not include an error control system",
"children": [
{
"content": "> AMTOR is similar to RTTY but with error correction added; a special 7-bit code is used. Amateur Teleprinting Over Radio (AMTOR) can run under two modes. Mode B ( FEC - Forward Error Correction ): characters are sent twice in groups of five in consecutive blocks. Mode A ( ARQ - Automatic Repeat reQuest ): characters are transmitted in blocks of 3, receiving station returns a positive acknowledgement or a request to resend. [ Frame Check Sequence is part of the AX.25 Packet protocol, no relation to AMTOR ]"
}
]
}
]
},
{
"content": "AMTOR FEC - characters sent twice",
"children": [
{
"content": "A-5-8-6 (B) What error-correction system is used in AMTOR FEC (Mode B)?\nA\tThe receiving station checks the frame check sequence (FCS) against the transmitted FCS\nB\tEach character is sent twice\nC\tMode B AMTOR does not include an error-correction system\nD\tThe receiving station automatically requests repeats when needed",
"children": [
{
"content": "> AMTOR is similar to RTTY but with error correction added; a special 7-bit code is used. Amateur Teleprinting Over Radio (AMTOR) can run under two modes. Mode B ( FEC - Forward Error Correction ): characters are sent twice in groups of five in consecutive blocks. Mode A ( ARQ - Automatic Repeat reQuest ): characters are transmitted in blocks of 3, receiving station returns a positive acknowledgement or a request to resend. [ Frame Check Sequence is part of the AX.25 Packet protocol, no relation to AMTOR ]"
}
]
}
]
},
{
"content": "APRS is for messaging, telemetry, and broadcast. It is not for ALE.",
"children": [
{
"content": "A-5-8-7 (A) APRS (Automatic Packet Reporting System) does NOT support which one of these functions?\nA\tAutomatic link establishment\nB\tTwo-way messaging\nC\tTelemetry\nD\tAmateur-specific local information broadcast\n> Key word: NOT. \"APRS is a digital communications information channel for Ham radio. (...) As a single national channel (...), it gives the mobile ham a place to monitor for 10 to 30 minutes in any area, at any time to capture what is happening in ham radio in the surrounding area. Announcements, Bulletins, Messages, Alerts, Weather, and of course a map of all this activity including objects, satellites, nets, meetings, hamfests, etc. (...) APRS also supports global call sign-to-call sign messaging (...)\" (www.aprs.org Bob Bruninga WB4APR). Automatic Link Establishment (ALE) is a standard for systems capable of automatically selecting a band and frequency from a list of channels for HF communications with a given similarly-equipped station."
}
]
},
{
"content": "CRC use a hash function",
"children": [
{
"content": "A-5-8-8 (C) Which algorithm may be used to create a Cyclic Redundancy Check (CRC)?\nA\tConvolution code\nB\tLempel-Ziv routine\nC\tHash function\nD\tDynamic Huffman code\n> \"A hash function is any algorithm that maps data of arbitrary length to data of a fixed length. (...) The values returned by a hash function are called hash values, hash codes, hash sums, checksums or simply hashes\" (Wikipedia). A convolutional code is a type of error-correcting code (e.g., Viterbi or Reed-Solomon). Lempel-Ziv and Dynamic Huffman coding are lossless data compression algorithms."
}
]
},
{
"content": "AX.25 is used for packet",
"children": [
{
"content": "A-5-8-9 (A) The designator AX.25 is associated with which amateur radio mode?\nA\tpacket\nB\tRTTY\nC\tASCII\nD\tspread spectrum speech\n> Packet radio adheres to the AX.25 protocol. AX.25 is derived from the X.25 networking protocol: one notable difference is the use of call signs as addresses. AX.25 uses a Frame-Check Sequence for error detection. The Frame-Check sequence (FCS) is a sixteen-bit number calculated by both the sending and receiving stations of a frame. Comparing the received FCS with a locally computed one permits detecting corruption in transit."
}
]
},
{
"content": "Spread-Spectrum Frequency-Hopping is a fucking thing",
"children": [
{
"content": "FHSS is a thing",
"children": [
{
"content": "A-5-9-8 (C) What is frequency hopping spread spectrum?\nA\tThe carrier is frequency-companded\nB\tThe carrier is phase-shifted by a fast binary bit stream\nC\tThe carrier frequency is changed in accordance with a pseudo-random list of channels\nD\tThe carrier is amplitude-modulated over a wide range called the spread",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
},
{
"content": "Spead spectrum is a thing",
"children": [
{
"content": "A-5-9-1 (B) What term describes a wide-band communications system in which the RF carrier varies according to some predetermined sequence?\nA\tTime domain frequency modulation\nB\t**Spread spectrum** communication\nC\tAmplitude-companded single sideband\nD\tAMTOR",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
},
{
"content": "It uses a pseuo-random sequence",
"children": [
{
"content": "A-5-9-11 (A) How does the spread-spectrum technique of frequency hopping work?\nA\tThe frequency of an RF carrier is changed very rapidly according to a particular pseudo-random sequence\nB\tIf interference is detected by the receiver, it will signal the transmitter to change frequency\nC\tIf interference is detected by the receiver, it will signal the transmitter to wait until the frequency is clear\nD\tA pseudo-random bit stream is used to shift the phase of an RF carrier very rapidly in a particular sequence",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
},
{
"content": "A-5-9-6 (D) Which type of signal is used to produce a predetermined alteration in the carrier for spread spectrum communication?\nA\tFrequency-companded sequence\nB\tQuantizing noise\nC\tRandom noise sequence\nD\t**Pseudo-random sequence**",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
},
{
"content": "Frequency hopping is a thing",
"children": [
{
"content": "A-5-9-2 (C) What is the term used to describe a spread spectrum communications system where the centre frequency of a conventional carrier is changed many times per second in accordance with a pseudorandom list of channels?\nA\tTime-domain frequency modulation\nB\tFrequency companded spread spectrum\nC\t**Frequency hopping**\nD\tDirect sequence",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
},
{
"content": "A-5-9-4 (C) Frequency hopping is used with which type of transmission?\nA\tPacket\nB\tRTTY\nC\t**Spread spectrum**\nD\tAMTOR",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
},
{
"content": "Direct sequence is a thing",
"children": [
{
"content": "A-5-9-3 (A) What term is used to describe a spread spectrum communications system in which a very fast binary bit stream is used to shift the phase of an RF carrier?\nA\tDirect sequence\nB\tFrequency hopping\nC\tPhase companded spread spectrum\nD\tBinary phase-shift keying",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
},
{
"content": "A-5-9-5 (D) Direct sequence is used with which type of transmission?\nA\tAMTOR\nB\tPacket\nC\tRTTY\nD\t**Spread spectrum**",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
},
{
"content": "It is difficult to monitor",
"children": [
{
"content": "A-5-9-7 (C) Why is it difficult to monitor a spread spectrum transmission?\nA\tIt varies too quickly in amplitude\nB\tThe signal is too distorted for comfortable listening\nC\tYour receiver must be **frequency-synchronized** to the transmitter\nD\tIt requires narrower bandwidth than most receivers have",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
},
{
"content": "direct-sequence is thing",
"children": [
{
"content": "A-5-9-9 (D) What is **direct-sequence** spread spectrum?\nA\tThe carrier is amplitude modulated over a range called the spread\nB\tThe carrier is frequency-companded\nC\tThe carrier is altered in accordance with a pseudo-random list of channels\nD\tThe carrier is phase-shifted by a fast binary bit stream",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
},
{
"content": "they are resistant to interference",
"children": [
{
"content": "A-5-9-10 (B) Why are received spread-spectrum signals so resistant to interference?\nA\tThe high power used by a spread-spectrum transmitter keeps its signal from being easily overpowered\nB\tSignals not using the spectrum-spreading algorithm are suppressed in the receiver\nC\tThe receiver is always equipped with a special digital signal processor (DSP) interference filter\nD\tIf interference is detected by the receiver, it will signal the transmitter to change frequencies",
"children": [
{
"content": "> Spread-spectrum transmission relies on a wide range of frequencies rather than a single one to reduce the effects of noise and interference. It requires several megahertz of bandwidth. Frequency-Hopping Spread-Spectrum changes the carrier frequency a number of times per second in a given pattern. Direct-Sequence Spread-Spectrum uses a pseudo-random bit pattern, many times faster than the data stream, to impress Phase Shift Keying on a carrier. For proper demodulation, the receiver must synchronize itself with the incoming stream. Noise and interference do not follow the same pre-agreed patterns and are thus effectively ignored."
}
]
}
]
}
]
}
]
},
{
"content": "\n{L14} Transmission Lines.",
"children": [
{
"content": "Tuners",
"children": [
{
"content": "there are "
},
{
"content": "A-7-1-1 (D) For an antenna tuner of the \"Transformer\" type, which of the following statements is FALSE?\nA\tThe input is suitable for 50 ohm impedance\nB\tThe output is suitable for impedances from low to high\nC\tThe circuit is known as a transformer-type antenna tuner\nD\tThe circuit is known as a Pi-type antenna tuner",
"children": [
{
"content": "> A tuning circuit using two inductively-coupled windings can readily effect an impedance transformation like a transformer. The coupling may be fixed or variable. Moving a tap on the output coil changes the turns ratio and permits raising or lowering impedance."
}
]
},
{
"content": "A-7-1-2 (C) For an antenna tuner of the \"Series\" type, which of the following statements is false?\nA\tThe output is suitable for impedances from low to high\nB\tThe input is suitable for impedance of 50 ohms\nC\tThe circuit is known as a Pi-type antenna tuner\nD\tThe circuit is known as a Series-type antenna tuner",
"children": [
{
"content": "> A simple series L-C network is one of the ways to couple a random-length antenna, whose impedance can be quite unpredictable, directly to a transmitter. Other options include the L and Pi networks."
}
]
},
{
"content": "L-match",
"children": [
{
"content": "A-7-1-3 (B) For an antenna tuner of the \"L\" type, which of the following statements is false?\nA\tThe circuit is known as an L-type antenna tuner\nB\tThe circuit is suitable for matching to a vertical ground plane antenna\nC\tThe transmitter input is suitable for 50 ohms impedance\nD\tThe antenna output is high impedance",
"children": [
{
"content": "> A resonant vertical ground plane antenna offers an impedance in the range 30 to 50 ohms. A low-pass \"L\" network (series inductor followed by parallel capacitor) is commonly used with a high impedance random wire. With only two variables components, an \"L\" network has a limited range of impedance transformation. [ In reality, four \"L\" configurations are possible, two of which can match to a lower impedance. ]"
}
]
}
]
},
{
"content": "Pi-match",
"children": [
{
"content": "A-7-1-4 (B) For an antenna tuner of the \"Pi\" type, which of the following statements is false?\nA\tThe circuit is a Pi-type antenna tuner\n~~B\tThe circuit is a series-type antenna tuner~~\nC\tThe transmitter input is suitable for impedance of 50 ohms\nD\tThe antenna output is suitable for impedances from low to high",
"children": [
{
"content": "> The \"Pi\" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network."
}
]
}
]
}
]
},
{
"content": "Matching Networks",
"children": [
{
"content": "A-7-1-5 (A) What is a pi-network?\nA\tA network consisting of one inductor and two capacitors or two inductors and one capacitor\nB\tAn antenna matching network that is isolated from ground\nC\tA network consisting of four inductors or four capacitors\nD\tA power incidence network",
"children": [
{
"content": "> The \"Pi\" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network."
}
]
},
{
"content": "A-7-1-6 (D) Which type of network offers the greatest transformation ratio?\nA\tChebyshev\nB\tButterworth\nC\tL-network\nD\tPi-network",
"children": [
{
"content": "> With only two variables components, an \"L\" network has a limited range of impedance transformation. The \"Pi\" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network. The \"Pi-L\" network, where the Pi output capacitor doubles as an input capacitor to a subsequent L section, provides even more harmonic suppression and a greater transformation ratio."
}
]
},
{
"content": "A-7-1-7 (B) Why is an L-network of limited utility in impedance matching?\nA\tIt has limited power handling capability\nB\tIt matches only a small impedance range\nC\tIt is thermally unstable\nD\tIt is prone to self-resonance",
"children": [
{
"content": "> With only two variables components, an \"L\" network has a limited range of impedance transformation. The \"Pi\" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network. The \"Pi-L\" network, where the Pi output capacitor doubles as an input capacitor to a subsequent L section, provides even more harmonic suppression and a greater transformation ratio."
}
]
},
{
"content": "A-7-1-8 (A) How does a network transform one impedance to another?\nA\tIt cancels the reactive part of an impedance and changes the resistive part\nB\tIt produces transconductance to cancel the reactive part of an impedance\nC\tIt introduces negative resistance to cancel the resistive part of an impedance\nD\tNetwork resistances substitute for load resistances",
"children": [
{
"content": "> Within the context of matching the line to a transmitter, the goal is to present a suitable resistive impedance to the final amplifier. Impedance comprises a reactive value and a resistive value. To achieve matching, reactance must be cancelled and resistance transformed."
}
]
},
{
"content": "A-7-1-9 (B) What advantage does a pi-L network have over a pi-network for impedance matching between a vacuum tube linear amplifier and a multiband antenna?\nA\tGreater transformation range\nB\tGreater harmonic suppression\nC\tHigher efficiency\nD\tLower losses",
"children": [
{
"content": "> Key words: MULTIBAND ANTENNA. Such an antenna may radiate harmonics more readily. The added harmonic suppression of the \"Pi-L\" network is advantageous."
}
]
},
{
"content": "A-7-1-10 (D) Which type of network provides the greatest harmonic suppression?\nA\tInverse pi-network\nB\tPi-network\nC\tL-network\nD\tPi-L network",
"children": [
{
"content": "> With only two variables components, an \"L\" network has a limited range of impedance transformation. The \"Pi\" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network. The \"Pi-L\" network, where the Pi output capacitor doubles as an input capacitor to a subsequent L section, provides even more harmonic suppression and a greater transformation ratio."
}
]
}
]
},
{
"content": "Stubs",
"children": [
{
"content": "A-7-2-1 (B) What kind of impedance does a quarter wavelength transmission line present to the source when the line is shorted at the far end?\nA\tA very low impedance\nB\tA very high impedance\nC\tThe same as the characteristic impedance of the transmission line\nD\tThe same as the output impedance of the source",
"children": [
{
"content": "> Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a \"Q Section\" or \"Quarter-Wave Transformer\"."
}
]
},
{
"content": "A-7-2-2 (D) What kind of impedance does a quarter wavelength transmission line present to the source if the line is open at the far end?\nA\tA very high impedance\nB\tThe same as the output impedance of the source\nC\tThe same as the characteristic impedance of the transmission line\nD\tA very low impedance",
"children": [
{
"content": "> Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a \"Q Section\" or \"Quarter-Wave Transformer\"."
}
]
},
{
"content": "A-7-2-3 (A) What kind of impedance does a half wavelength transmission line present to the source when the line is open at the far end?\nA\tA very high impedance\nB\tThe same as the characteristic impedance of the transmission line\nC\tThe same as the output impedance of the source\nD\tA very low impedance",
"children": [
{
"content": "> Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a \"Q Section\" or \"Quarter-Wave Transformer\"."
}
]
},
{
"content": "A-7-2-4 (B) What kind of impedance does a half wavelength transmission line present to the source when the line is shorted at the far end?\nA\tThe same as the output impedance of the source\nB\tA very low impedance\nC\tA very high impedance\nD\tThe same as the characteristic impedance of the transmission line",
"children": [
{
"content": "> Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a \"Q Section\" or \"Quarter-Wave Transformer\"."
}
]
}
]
},
{
"content": "Velocity Factor",
"children": [
{
"content": "For a given wavelength, the cable is shorter than the wave in free space.",
"children": [
{
"content": "A-7-2-9 (D) Why is the physical length of a coaxial cable shorter than its electrical length?\nA\tThe surge impedance is higher in the parallel transmission line\nB\tSkin effect is less pronounced in the coaxial cable\nC\tThe characteristic impedance is higher in a parallel transmission line\nD\tRF energy moves slower along the coaxial cable than in air",
"children": [
{
"content": "> Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically."
}
]
}
]
},
{
"content": "velocity factor nu\n\nv = nu c\n\nnu = v/c",
"children": [
{
"content": "A-7-2-6 (C) What is the term for the **ratio** of the actual velocity at which a signal travels through a transmission line to the speed of light in a vacuum?\nA\tSurge impedance\nB\tStanding wave ratio\nC\tVelocity factor\nD\tCharacteristic impedance",
"children": [
{
"content": "> Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically."
}
]
},
{
"content": "A-7-2-5 (A) What is the velocity factor of a transmission line?\nA\tThe velocity of the wave on the transmission line **divided by** the velocity of light\nB\tThe velocity of the wave on the transmission line multiplied by the velocity of light in a vacuum\nC\tThe index of shielding for coaxial cable\nD\tThe ratio of the characteristic impedance of the line to the terminating impedance",
"children": [
{
"content": "> Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically."
}
]
},
{
"content": "A-7-2-11 (C) The velocity factor of a transmission line is the:\nA\tspeed at which the signal travels in free space\nB\tspeed to which the standing waves are reflected back to the transmitter\nC\t**ratio** of the velocity of propagation in the transmission line to the velocity of propagation in free space\nD\timpedance of the line, e.g. 50 ohm, 75 ohm, etc.",
"children": [
{
"content": "> Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.\n\n' -- -- -- --"
}
]
}
]
},
{
"content": "velocity factor is the factor by which a free-space wavelength is multiplied to obtain the length in a medium.\n\nlambda_free * vf = lambda_medium\n\nso\n```\n lambda_free\nvf = -------------\n lambda_medium\n```",
"children": [
{
"content": "for example, at 14.1 MHz `lambda = ~20 m`, \nwith `vf = 0.66` then\n`20 m * 0.66 = about 12 m`; \na quarter of that is about `3 m`",
"children": [
{
"content": "A-7-3-4 (C) Assuming a velocity factor of 0.66 what would be the physical length of a typical coaxial stub that is electrically one quarter wavelength long at 14.1 MHz?\nA\t2.33 metres (7.64 feet)\nB\t0.25 metre (0.82 foot)\nC\t3.51 metres (11.5 feet)\nD\t20 metres (65.6 feet)",
"children": [
{
"content": "> An electrical quarter wavelength can be computed in metres as one fourth of 300 divided by frequency in megahertz. The physical length equals the electrical length times the Velocity Factor. In this example, 300 divided by 14.1 divided by 4 times 0.66 = 3.51 metre."
}
]
}
]
}
]
},
{
"content": "velocity factor is determined by the dielectric material, with the following relationship:\n\nnu = 1/sqrt(C_d)",
"children": [
{
"content": "A-7-2-8 (A) What determines the velocity factor in a transmission line?\nA\tDielectrics in the line\nB\tThe line length\nC\tThe centre conductor resistivity\nD\tThe terminal impedance",
"children": [
{
"content": "> Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically."
}
]
},
{
"content": "A-7-2-10 (C) The reciprocal of the square root of the dielectric constant of the material used to separate the conductors in a transmission line gives the ____________ of the line:\nA\timpedance\nB\thermetic losses\nC\tvelocity factor\nD\tVSWR",
"children": [
{
"content": "> Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically."
}
]
}
]
},
{
"content": "Typ nu=.66",
"children": [
{
"content": "A-7-2-7 (A) What is a typical velocity factor for coaxial cable with polyethylene dielectric?\nA\t0.66\nB\t0.33\nC\t0.1\nD\t2.7",
"children": [
{
"content": "> Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically."
}
]
}
]
}
]
},
{
"content": "Waveguides",
"children": [
{
"content": "Waveguides are used above 3 GHz.",
"children": [
{
"content": "A-7-9-1 (A) Waveguide is typically used:\nA\tat frequencies above 3000 MHz\nB\tat frequencies above 2 MHz\nC\tat frequencies below 150 MHz\nD\tat frequencies below 1500 MHz",
"children": [
{
"content": "> Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies."
}
]
}
]
},
{
"content": "Above the cutoff/critical frequency (e.g. for microwaves) waveguides have low loss.",
"children": [
{
"content": "A-7-9-6 (A) Which of the following is a major advantage of waveguide over coaxial cable for use at microwave frequencies?\nA\t**Very low losses**\nB\tFrequency response from 1.8 MHz to 24GHz\nC\tEasy to install\nD\tInexpensive to install",
"children": [
{
"content": "> Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies."
}
]
}
]
},
{
"content": "Waveguides are low-loss.",
"children": [
{
"content": "A-7-9-3 (B) Which of the following is an advantage of waveguide as a transmission line?\nA\tHeavy and difficult to install\nB\tLow loss\nC\tFrequency sensitive based on dimensions\nD\tExpensive",
"children": [
{
"content": "> Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies."
}
]
}
]
},
{
"content": "There is no such thing as hysteresis loss.",
"children": [
{
"content": "A-7-9-2 (D) Which of the following is not correct? Waveguide is an efficient transmission medium because it features:\nA\tlow radiation loss\nB\tlow dielectric loss\nC\tlow copper loss\nD\tlow hysteresis loss",
"children": [
{
"content": "> Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies."
}
]
}
]
},
{
"content": "Waveguides are a half-wavelengh wide.",
"children": [
{
"content": "A-7-9-4 (D) For rectangular waveguide to transfer energy, the cross-section should be at least:\nA\tthree-eighths wavelength\nB\tone-eighth wavelength\nC\tone-quarter wavelength\nD\tone-half wavelength",
"children": [
{
"content": "> Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies."
}
]
}
]
},
{
"content": "Waveguides only support transmission above the \"critical\" or \"cutoff\" frequency, so they are in effect a **high-pass filter**.",
"children": [
{
"content": "A-7-9-9 (D) A section of waveguide:\nA\toperates like a low-pass filter\nB\toperates like a band-stop filter\nC\tis lightweight and easy to install\nD\toperates like a high-pass filter",
"children": [
{
"content": "> Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies."
}
]
},
{
"content": "A-7-9-5 (D) Which of the following statements about waveguide IS NOT correct?\nA\tIn the transverse electric mode, a component of the magnetic field is in the direction of propagation\nB\tIn the transverse magnetic mode, a component of the electric field is in the direction of propagation\nC\tWaveguide has low loss at high frequencies, but high loss below cutoff frequency\nD\tWaveguide has high loss at high frequencies, but low loss below cutoff frequency",
"children": [
{
"content": "> Key words: IS NOT. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. In free space, waves are known as transverse-electromagnetic: the electric field, the magnetic field and the direction of travel are all perpendicular to one another. In a waveguide, waves bounce from wall to wall thus travelling in a zigzag manner. Only one of the electric or magnetic field can be truly perpendicular with the length of the waveguide; the mode, transverse electric or transverse magnetic, describes which field is purely perpendicular."
}
]
}
]
},
{
"content": "Because waveguides carry heating microwaves, be careful.",
"children": [
{
"content": "A-7-9-11 (C) What precautions should you take before beginning repairs on a microwave feed horn or waveguide?\nA\tBe sure propagation conditions are unfavourable for tropospheric ducting\nB\tBe sure to wear tight-fitting clothes and gloves to protect your body and hands from sharp edges\nC\tBe sure the transmitter is turned off and the power source is disconnected\nD\tBe sure the weather is dry and sunny",
"children": [
{
"content": "> With the possibility of shorter wavelengths to reach deeper into the body or to produce resonances in smaller structures, such as the eye, be extra careful not to expose anyone to microwave radiation. The significant gain available from physically small antennas also turn low power levels into definite risks. Heating is one known effect of RF on body tissues, other effects are possible."
}
]
}
]
}
]
},
{
"content": "Stripline & microstripline",
"children": [
{
"content": "\"Stripline\" is basically a specially sized trace on a PCB surrounded by ground layers, above and below.",
"children": [
{
"content": "A-7-9-7 (B) What is **printed circuit** transmission line called?\nA\tGround plane\nB\tMicrostripline\nC\tDielectric substrate\nD\tDielectric imprinting",
"children": [
{
"content": "> A Microstrip transmission line is a type of line consisting of a thin and flat strip of conductive material separated from a ground plane by a dielectric. A double-sided printed circuit board lends itself to the construction of microstrip lines: traces on top with a ground plane underneath. Characteristic Impedance is determined by trace width, dielectric thickness and dielectric constant. One side of the line is exposed to air, external shielding may be required when high isolation is required. Stripline uses a similar thin and flat conductor but sandwiched between two parallel ground planes."
}
]
},
{
"content": "A-7-9-10 (B) Stripline is a:\nA\tfamily of fluids for removing coatings from small parts\nB\t**printed circuit** transmission line\nC\tsmall semiconductor family\nD\thigh power microwave antenna",
"children": [
{
"content": "> A Microstrip transmission line is a type of line consisting of a thin and flat strip of conductive material separated from a ground plane by a dielectric. A double-sided printed circuit board lends itself to the construction of microstrip lines: traces on top with a ground plane underneath. Characteristic Impedance is determined by trace width, dielectric thickness and dielectric constant. External shielding may be required when high isolation is required. Stripline uses a similar thin and flat conductor but sandwiched between two parallel ground planes."
}
]
}
]
},
{
"content": "***micro*stripline** omits the second shield layer, and consequently has poorer shielding",
"children": [
{
"content": "A-7-9-8 (B) Compared with coaxial cable, **microstripline**:\nA\tmust have much higher characteristic impedance\nB\thas **poorer shielding**\nC\thas superior shielding\nD\tmust have much lower characteristic impedance",
"children": [
{
"content": "> A Microstrip transmission line is a type of line consisting of a thin and flat strip of conductive material separated from a ground plane by a dielectric. A double-sided printed circuit board lends itself to the construction of microstrip lines: traces on top with a ground plane underneath. Characteristic Impedance is determined by trace width, dielectric thickness and dielectric constant. One side of the line is exposed to air, external shielding may be required when high isolation is required. Stripline uses a similar thin and flat conductor but sandwiched between two parallel ground planes."
}
]
}
]
}
]
},
{
"content": "Smith Charts",
"children": [
{
"content": "A-7-1-11 (C) A Smith Chart is useful:\nA\tto solve problems in direct current circuits\nB\tbecause it only works with complex numbers\nC\tbecause it simplifies mathematical operations\nD\tonly to solve matching and transmission line problems",
"children": [
{
"content": "> \"The Smith chart, invented by Phillip H. Smith (1905–1987), is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. (...) The Smith chart is most frequently used at or within the unity radius region. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis\". (Wikipedia)"
}
]
}
]
}
]
},
{
"content": "\n{L16} FM Repeaters.",
"children": [
{
"content": "Intermod `!`",
"children": [
{
"content": "intermodulation refers to mixing of outside signals",
"children": [
{
"content": "A-5-6-1 (B) If the signals of two repeater transmitters mix together in one or both of their final amplifiers and unwanted signals at the sum and difference frequencies of the original signals are generated and radiated, what is this called?\nA\tAmplifier desensitization\nB\t**Intermodulation interference**\nC\tNeutralization\nD\tAdjacent channel interference",
"children": [
{
"content": "> Intermodulation is the unwanted mixing of two or more signals that produce new signals (products). The fundamental or harmonic energy from strong nearby transmitters intermix to create intermodulation products. Mixing can take place in the front-end of the affected receiver, in the Power Amplifier of one of the transmitters or through \"external rectification or passive intermodulation\" (in some electronic device or some corroded junction between two metals acting as a diode mixer)."
}
]
}
]
},
{
"content": "This happens when you have two tranmsitters next to each other",
"children": [
{
"content": "A-5-6-2 (A) How does intermodulation interference between two repeater transmitters usually occur?\nA\tWhen they are in close proximity and the signals mix in one or both of their final amplifiers\nB\tWhen the signals are reflected in phase by aircraft passing overhead\nC\tWhen they are in close proximity and the signals cause feedback in one or both of their final amplifiers\nD\tWhen the signals are reflected out of phase by aircraft passing overhead",
"children": [
{
"content": "> Intermodulation is the unwanted mixing of two or more signals that produce new signals (products). The fundamental or harmonic energy from strong nearby transmitters intermix to create intermodulation products. Mixing can take place in the front-end of the affected receiver, in the Power Amplifier of one of the transmitters or through \"external rectification or passive intermodulation\" (in some electronic device or some corroded junction between two metals acting as a diode mixer)."
}
]
}
]
},
{
"content": "It can be prevented by the use of a device called a **terminated circulator**, also called a line isolator",
"children": [
{
"content": "A-5-6-3 (B) How can intermodulation interference between two repeater transmitters in close proximity often be reduced or eliminated?\nA\tBy using a Class C final amplifier with high driving power\nB\tBy installing a terminated **circulator** or ferrite isolator in the transmission line to the transmitter and duplexer\nC\tBy installing a low-pass filter in the antenna transmission line\nD\tBy installing a high-pass filter in the antenna transmission line",
"children": [
{
"content": "> A circulator is usually a three-port device; any energy coming in one port is forwarded in one direction only, towards the next port. An isolator is a circulator with one port terminated into a dummy load. With the transmitter on port 1, the antenna on port 2 and a dummy load on port 3, RF from the transmitter is routed to the antenna but any outside energy picked-up by the antenna is diverted to the dummy load and thus cannot enter the Power Amplifier where it might lead to intermodulation. Magnetized ferrite material is used in the fabrication of circulators."
}
]
}
]
},
{
"content": "`!` IMD results from the mixing of harmonics; involving the sum and difference of *harmonics* of two interfering signals.",
"children": [
{
"content": "for example, IMD on 146.70 due to signals on 146.52 and may be due to signals on 146.34 MHz or 146.61 MHz",
"children": [
{
"content": "A-5-6-4 (D) If a receiver tuned to 146.70 MHz receives an intermodulation product signal whenever a nearby transmitter transmits on 146.52, what are the two most likely frequencies for the other interfering signal?\nA\t146.88 MHz and 146.34 MHz\nB\t146.01 MHz and 147.30 MHz\nC\t73.35 MHz and 239.40 MHz\nD\t**146.34 MHz** and **146.61 MHz**",
"children": [
{
"content": "> Third Order Intermodulation products where the second harmonic of one signal mixes with the fundamental frequency of another are the most troublesome because of the relative frequency proximity of the involved signals: filtering them out is difficult. Given two signals, F1 and F2, the Third Order IMD product can be computed as (a) \"twice F1 minus F2\" or (b) \"twice F2 minus F1\". In this example, IMD = 146.70, F1 = 146.52 ; solving for F2 in case \"a\" is (F1 times 2), minus IMD ; solving for F2 in case \"b\" is (IMD + F1), divided by 2."
}
]
}
]
},
{
"content": "146.70 is ...?\n\ndouble the interfering signal:\n146.52 = 293.04\n\n293.04 - 146.70 = 146.34 one possible interfering signal\n\nbecause\n146.70 = 2*146.520 - 146.34\n\n\nAnother possibility: \n146.70 = 146.520 +/- 2 X\n\nSo (146.520 146.70 - "
}
]
},
{
"content": "Cavity filters are used for 2 m repeaters.",
"children": [
{
"content": "A-5-6-7 (D) Which type of filter would be best to use in a 2-metre repeater duplexer?\nA\tA DSP filter\nB\tAn L-C filter\nC\tA crystal filter\nD\tA cavity filter",
"children": [
{
"content": "> In the context of a repeater installation, a duplexer is a specialized filter which allows operating the receiver and transmitter simultaneously on the same antenna. The duplexer is built with four or more quarter-wavelength cavity resonators. The duplexer provides isolation ( 90 dB or more on 2 m ) between the receive and transmit paths at the expense of insertion loss."
}
]
}
]
},
{
"content": "IMD occurs in final amplifers and receiver front-ends, but not IF stages (this is presumably due to filtering between stages).",
"children": [
{
"content": "A-5-6-11 (A) Intermodulation interference products are **not** typically associated with which of the following:\nA\t**intermediate frequency stage**\nB\tfinal amplifier stage\nC\treceiver frontend\nD\tpassive intermodulation\n> \"Undesired mixing of two or more frequencies in a non-linear device which produces additional sum and difference frequencies\" (ARRL RFI Book). Final amplifier stage: signals from nearby transmitters may find their way into a power amplifier creating intermodulation. Receiver front-end: strong offending signals may enter the RF amplifier or mixer and create intermodulation. Passive intermodulation (PIM), sometimes called \"rusty bolt effect\": passive devices subjected to strong signals cause the problem; cables, antennas, connectors, dissimilar metals, etc. due to oxidation, corrosion, metal flakes, dirty mating surfaces or poor contact."
}
]
}
]
}
]
},
{
"content": "\n{L15} Antennas.",
"children": [
{
"content": "antenna feed matches",
"children": [
{
"content": "[stub match uses a short section (stub) of feedline\n\nhttps://en.wikipedia.org/wiki/Stub_(electronics)\nhttps://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer",
"children": [
{
"content": "A-7-3-3 (A) What term describes a method of antenna impedance matching that uses a short section of transmission line connected to the antenna transmission line near the antenna and perpendicular to the transmission line?\nA\tThe **stub** match\nB\tThe omega match\nC\tThe delta match\nD\tThe gamma match",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
},
{
"content": "For example, a quarter wave stub at 15 Mhz using vf = 0.8 cable\n\n```\nv = f l\n\nl = c nu / f\n\nl = 300 10^6 * .8 / 15 10^6\n = 300 * .8 / 15 [m]\n = 16 [m]\n\nso 1/4 l = 4 [m]\n```",
"children": [
{
"content": "A-7-3-6 (A) A quarter-wave stub, for use at 15 MHz, is made from a coaxial cable having a velocity factor of 0.8. Its physical length will be:\nA\t**4 m** (13.1 ft)\nB\t12 m (39.4 ft)\nC\t8 m (26.2 ft)\nD\t7.5 m (24.6 ft)",
"children": [
{
"content": "> An electrical quarter wavelength can be computed in metres as one fourth of 300 divided by frequency in megahertz. The physical length equals the electrical length times the Velocity Factor. In this example, 300 divided by 15 divided by 4 times 0.80 = 4 metres."
}
]
}
]
}
]
},
{
"content": "T-match matches high-impedance balanced transmission line (ladder line) to a low-impedance element",
"children": [
{
"content": "A-7-3-1 (C) What term describes a method used to match a high-impedance transmission line to a lower impedance antenna by connecting the line to the driven element in two places, spaced a fraction of a wavelength on each side of the driven element centre?\nA\tThe omega match\nB\tThe stub match\nC\tThe **T match**\nD\tThe gamma match",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
}
]
},
{
"content": "The gamma match is basically half a t-match. gamma match is where you connect the center conductor of an unbalanced feedline in two special places on the driven element.",
"children": [
{
"content": "A-7-3-2 (C) What term describes an **unbalanced** feed system in which the driven element of an antenna is fed both **at the centre** and a fraction of a wavelength **to one side** of centre?\nA\tThe stub match\nB\tThe T match\nC\tThe **gamma** match\nD\tThe omega match",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
}
]
},
{
"content": "yagi-uda gamma match",
"children": [
{
"content": "A-7-3-11 (A) A Yagi antenna uses a gamma match. The variable capacitor connects to the:\nA\tadjustable gamma rod\nB\tan adjustable point on the director\nC\tcenter of the driven element\nD\tcoaxial line braid",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
},
{
"content": "A-7-3-10 (C) A Yagi antenna uses a gamma match. The adjustable gamma rod connects to:\nA\tan adjustable point on the reflector\nB\tthe centre of the driven element\nC\tthe variable capacitor\nD\tthe coaxial line centre conductor",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
},
{
"content": "A-7-3-9 (C) A Yagi antenna uses a gamma match. The centre of the driven element connects to:\nA\tthe adjustable gamma rod\nB\ta variable capacitor\nC\tthe coaxial line braid\nD\tthe coaxial line centre conductor",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
},
{
"content": "A-7-3-8 (C) A Yagi antenna uses a gamma match. The coaxial braid connects to:\nA\tthe adjustable gamma rod\nB\tthe centre of the reflector\nC\tthe centre of the driven element\nD\tthe variable capacitor",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
},
{
"content": "A-7-3-7 (D) The matching of a driven element with a single adjustable mechanical and capacitive arrangement is descriptive of:\nA\ta \"T\" match\nB\tan \"omega\" match\nC\ta \"Y\" match\nD\ta \"gamma\" match",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
},
{
"content": "A-7-3-5 (B) The driven element of a Yagi antenna is connected to a coaxial transmission line. The coax braid is connected to the centre of the driven element and the centre conductor is connected to a variable capacitor in series with an adjustable mechanical arrangement on one side of the driven element. The type of matching is:\nA\tzeta match\nB\t**gamma match**\nC\tlambda match\nD\tT match",
"children": [
{
"content": "> Gamma match: an unbalanced feed system, the coaxial braid attaches to the centre of the radiating element, the centre conductor connects via a series capacitor further along the radiating element. This second connection is done with an adjustable rod parallel to the radiating element. T match: a balanced feed system, can be thought as two mirrored gamma matches, the feed line is brought via conductors parallel to the radiating element at points further along the element. A Matching Stub is a short section of line, open or shorted, connected across the transmission line at a specific distance from the antenna feedpoint."
}
]
}
]
}
]
},
{
"content": "half-wave dipole",
"children": [
{
"content": "A-7-4-10 (D) In a half-wave dipole, where does the minimum current occur?\nA\tAt the centre\nB\tIt is equal at all points\nC\tAt the right end\nD\tAt both ends",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-11 (B) In a half-wave dipole, where does the minimum impedance occur?\nA\tAt both ends\nB\tAt the centre\nC\tIt is the same at all points\nD\tAt the right end",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-9 (B) In a half-wave dipole, where does minimum voltage occur?\nA\tBoth ends\nB\tThe centre\nC\tAt the right end\nD\tIt is equal at all points",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-8 (C) The impedance of a half-wave antenna at its centre is low, because at this point:\nA\tvoltage and current are both low\nB\tvoltage is high and current is low\nC\tvoltage is low and current is high\nD\tvoltage and current are both high",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-7 (C) At the ends of a half-wave dipole:\nA\tvoltage and current are both low\nB\tvoltage is low and current is high\nC\tvoltage is high and current is low\nD\tvoltage and current are both high",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-6 (D) A half-wave dipole antenna is normally fed at the point where:\nA\tthe voltage is maximum\nB\tthe resistance is maximum\nC\tthe antenna is resonant\nD\tthe current is maximum",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-5 (A) In a half-wave dipole, the highest distribution of ________ occurs at the middle.\nA\tcurrent\nB\tinductance\nC\tvoltage\nD\tcapacity",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-4 (A) In a half-wave dipole, the lowest distribution of _________ occurs at the middle.\nA\tvoltage\nB\tcapacity\nC\tinductance\nD\tcurrent",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-3 (C) The feed point in a centre-fed half-wave antenna is at the point of:\nA\tminimum voltage and current\nB\tmaximum voltage\nC\tmaximum current\nD\tminimum current",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-2 (B) In a half-wave dipole, the distribution of _______ is lowest at each end.\nA\tcapacitance\nB\tcurrent\nC\tvoltage\nD\tinductance",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
},
{
"content": "A-7-4-1 (D) In a half-wave dipole, the distribution of _______ is highest at each end.\nA\tcurrent\nB\tinductance\nC\tcapacitance\nD\tvoltage",
"children": [
{
"content": "> On a centre-fed resonant half-wave dipole, current is high and voltage low at the feedpoint, the ends exhibit high voltage and low current. Low voltage and high current at the centre make for low impedance ( Z = E divided by I )."
}
]
}
]
},
{
"content": "circular polarization",
"children": [
{
"content": "A-7-5-1 (D) What is meant by circularly polarized electromagnetic waves?\nA\tWaves with an electric field bent into circular shape\nB\tWaves that circle the earth\nC\tWaves produced by a circular loop antenna\nD\tWaves with a rotating electric field",
"children": [
{
"content": "> The polarization of an electromagnetic radio wave corresponds to the position of the electrical field with respect to the surface of the Earth: horizontal when the E field is parallel to ground and vertical when perpendicular to ground. The magnetic field is at 90 degrees (perpendicular) to the electrical field. Dipoles and Yagis are linearly polarized antennas (i.e., the electrical field has a constant orientation). Circular polarization, where the polarization rotates, can be obtained from helical beam antennas or with crossed linear antennas fed with the correct phase difference. \"Sense\" refers to the direction of the rotation: clockwise polarization for a receding wave is termed right-hand."
}
]
},
{
"content": "A-7-5-2 (A) What type of polarization is produced by crossed dipoles fed 90 degrees out of phase?\nA\tCircular polarization\nB\tCross-polarization\nC\tPerpendicular polarization\nD\tNone of the other answers, the two fields cancel out",
"children": [
{
"content": "> Crossed dipoles fed 90 degrees out of phase are the active elements of a turnstile antenna and produce circular polarization. The turnstile antenna is used for satellite communications."
}
]
},
{
"content": "A-7-5-3 (C) Which of these antennas does not produce circular polarization?\nA\tLindenblad antenna\nB\tAxial-mode helical antenna\nC\tLoaded helical-wound antenna\nD\tCrossed dipoles fed 90 degrees out of phase",
"children": [
{
"content": "> Key word: NOT. Antennas featuring a fine wire wound around a shaft (e.g., HF mobile antennas) are \"loaded helical-wound antennas\"; these produce a linear polarization, i.e., vertical or horizontal depending on their positions relative to ground. The axial-mode helical antenna, with its corkscrew look, is used in satellite work and produces circular polarization."
}
]
}
]
},
{
"content": "Cross-polarization loss is in the vicinity of 20 dB",
"children": [
{
"content": "A-7-5-5 (C) For VHF and UHF signals over a fixed path, what extra loss can be expected when linearly-polarized antennas are crossed-polarized (90 degrees)?\nA\t6 dB\nB\t10 dB\nC\t20 dB or more\nD\t3 dB",
"children": [
{
"content": "> \"A loss in signal strength of 20 dB or more can be expected with cross-polarization so it is important to use antennas with the same polarization as the stations with which you expect to communicate.\" (ARRL Antenna Book, 22nd ed., section 21.10.5 Polarization)"
}
]
}
]
},
{
"content": "ERP - relative to dipole\n\ndipole is ~2 dBi (i.e., relative to isotropic radiator)",
"children": [
{
"content": "A-7-6-11 (A) A transmitter has an output of 1000 watts PEP. The coaxial cable, connectors and antenna tuner have a composite loss of 1 dB, and the antenna gain is 10 dBd. What is the Effective Radiated Power (ERP) in watts PEP?\nA\t8000\nB\t1009\nC\t10 000\nD\t9000",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1 dB plus 10 dB yields a net increase of 9 dB or eight times the power."
}
]
},
{
"content": "A-7-6-10 (B) A transmitter has an output of 2000 watts PEP. The transmission line, connectors and antenna tuner have a composite loss of 1 dB, and the gain from the stacked Yagi antenna is 10 dBd. What is the Effective Radiated Power (ERP) in watts PEP?\nA\t2009\nB\t16 000\nC\t18 000\nD\t20 000",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1 dB plus 10 dB yields a net increase of 9 dB or eight times the power."
}
]
},
{
"content": "A-7-6-8 (D) A transmitter has a power output of 125 watts. There is a loss of 0.8 dB in the transmission line, 0.2 dB in the antenna tuner, and a gain of 10 dBd in the antenna. The Effective Radiated Power (ERP) is:\nA\t1250\nB\t1125\nC\t134\nD\t1000",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1 dB plus 10 dB yields a net increase of 9 dB or eight times the power."
}
]
},
{
"content": "A-7-6-6 (D) A transmitter has a power output of 100 watts. There is a loss of 1.30 dB in the transmission line, a loss of 0.2 dB through the antenna tuner, and a gain of 4.50 dBd in the antenna. The Effective Radiated Power (ERP) is:\nA\t800 watts\nB\t400 watts\nC\t100 watts\nD\t200 watts",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 1.5 dB plus 4.5 dB yields a net increase of 3 dB or twice the power."
}
]
},
{
"content": "A-7-6-5 (A) A transmitter has an output power of 200 watts. The coaxial and connector losses are 3 dB in total, and the antenna gain is 9 dBd. What is the approximate Effective Radiated Power of this system?\nA\t800 watts\nB\t3200 watts\nC\t1600 watts\nD\t400 watts",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 3 dB plus 9 dB yields a net increase of 6 dB or four times the power."
}
]
},
{
"content": "A-7-6-4 (A) Effective Radiated Power means the:\nA\ttransmitter output power, minus line losses, plus antenna gain relative to a dipole\nB\tpower supplied to the antenna before the modulation of the carrier\nC\tpower supplied to the transmission line plus antenna gain\nD\tratio of signal output power to signal input power",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain."
}
]
},
{
"content": "A-7-6-3 (A) What is the Effective Radiated Power of an amateur transmitter, if the transmitter output power is 200 watts, the transmission line loss is 5 watts, and the antenna power gain is 3 dBd?\nA\t390 watts\nB\t197 watts\nC\t228 watts\nD\t178 watts",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 5 watts plus 3 dB yields a net increase of 3 dB or twice the remaining power of 195 watts."
}
]
}
]
},
{
"content": "polarization chirality",
"children": [
{
"content": "A-7-5-8 (D) A helical-beam antenna with right-hand polarization will best receive signals with:\nA\tleft-hand polarization\nB\tvertical polarization only\nC\thorizontal polarization\nD\tright-hand polarization",
"children": [
{
"content": "> The helical beam antenna is circularly polarized. Although it will respond to horizontally or vertically polarized waves, the full gain of the antenna can only be realized with a circularly polarized wave of the same \"sense\"."
}
]
}
]
},
{
"content": "line losses consist of dielectric loss, and conductor loss",
"children": [
{
"content": "A-7-6-2 (D) As standing wave ratio rises, so does the loss in the transmission line. This is caused by:\nA\thigh antenna currents\nB\thigh antenna voltage\nC\tleakage to ground through the dielectric\nD\tdielectric and conductor heat losses",
"children": [
{
"content": "> Voltage peaks on the standing wave increase losses through the dielectric ( P = E squared divided by R ), current peaks on the standing wave increase conductor losses ( P = I squared times R )."
}
]
}
]
},
{
"content": "ERP\nERP",
"children": [
{
"content": "A-7-6-9 (A) If a 3 dBd gain antenna is replaced with a 9 dBd gain antenna, with no other changes, the Effective Radiated Power (ERP) will increase by:\nA\t4\nB\t6\nC\t1.5\nD\t2",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, an added 6 dB yields four times the power."
}
]
},
{
"content": "A-7-6-1 (D) A transmitter has an output of 100 watts. The cable and connectors have a composite loss of 3 dB, and the antenna has a gain of 6 dBd. What is the Effective Radiated Power?\nA\t350 watts\nB\t400 watts\nC\t300 watts\nD\t200 watts",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, minus 3 dB plus 6 dB yields a net increase of 3 dB or twice the power."
}
]
},
{
"content": "A-7-6-7 (B) If the overall gain of an amateur station is increased by 3 dB the ERP (Effective Radiated Power) will:\nA\tbe cut in half\nB\tdouble\nC\tdecrease by 3 watts\nD\tremain the same",
"children": [
{
"content": "> Effective Radiated Power (ERP) equals transmitter power minus line losses plus antenna gain. In this example, a net gain of 3 dB yields twice the power."
}
]
}
]
},
{
"content": "cross polarized antennas",
"children": [
{
"content": "A-7-5-9 (A) One antenna which will respond simultaneously to vertically- and horizontally-polarized signals is the:\nA\thelical-beam antenna\nB\tfolded dipole antenna\nC\tground-plane antenna\nD\tquad antenna",
"children": [
{
"content": "> The dipole, ground-plane and quad are all linearly polarized and thus respond optimally to waves polarized in a single given direction, horizontal or vertical as the case may be. Unless proper alignment is assured, a significant loss is incurred. The helical beam antenna is circularly polarized, it can deal with the rotating fields of a wave with circular polarization. Consequently, it can deal with any single polarization at any given angle."
}
]
}
]
},
{
"content": ""
},
{
"content": "polarization",
"children": [
{
"content": "A-7-7-2 (D) Most simple horizontally polarized antennas do not exhibit significant directivity unless they are:\nA\tan eighth of a wavelength above the ground\nB\ta quarter wavelength above the ground\nC\tthree-eighths of a wavelength above the ground\nD\ta half wavelength or more above the ground",
"children": [
{
"content": "> Below one half-wavelength in antenna height, there is little point in selecting a given broadside direction: for example, choosing a north-south orientation to favour east-west radiation will not pay significant dividends for antennas close to ground."
}
]
}
]
},
{
"content": "parabolic antennas",
"children": [
{
"content": "A-7-5-7 (B) A parabolic antenna is very efficient because:\nA\ta horn-type radiator can be used to trap the received energy\nB\tall the received energy is focused to a point where the pick-up antenna is located\nC\ta dipole antenna can be used to pick up the received energy\nD\tno impedance matching is required",
"children": [
{
"content": "> A parabolic reflector dish provides significant gain because energy striking any point of the parabola is reflected to the focal point with the correct phase. On transmit, the inverse process takes place: all energy directed at the parabola from the feed antenna is reflected forward with the correct phase. High gain antennas used on UHF or microwave frequencies present a real risk to living tissues: never stand in front of a transmitting antenna."
}
]
},
{
"content": "A-7-5-6 (C) Which of the following is NOT a valid parabolic dish illumination arrangement?\nA\tOffset feed\nB\tCassegrain\nC\tNewtonian\nD\tFront feed",
"children": [
{
"content": "> Key word: NOT. Front feed (also known as focal feed or axial feed): circular reflector, the feed is centered in front of the reflector, very common on larger dish antennas. Offset feed (also known as off-axis): elliptical reflector, the feed is off to one side, out of the path of the radio waves, typical of domestic satellite receiving antennas. Cassegrain (based on the Cassegrain telescope): the feed is behind the dish and relies on a small convex secondary reflector in front of the dish. Newtonian: a bogus answer, valid for telescopes."
}
]
},
{
"content": "Surface error should not be greater than a small fraction of wavelength",
"children": [
{
"content": "A-7-5-10 (D) In amateur work, what is the surface error upper limit you should try not to exceed on a parabolic reflector?\nA\t0.25 lambda\nB\t5 mm (0.2 in) regardless of frequency\nC\t1% of the diameter\nD\t0.1 lambda",
"children": [
{
"content": "> \"Surface errors should not exceed 1/8 lambda in amateur operation. At 430 MHz, 1/8 lambda is 3.4 inches [8.6 cm], but at 10 GHz, it is 0.1476 inch [3.7 mm]! (...) Mesh can be used for the reflector surface to reduce weight and wind loading, but hole size should be less than 1/12 lambda.\" (ARRL Antenna Book 22nd ed., sect. 15.6.2)"
}
]
}
]
},
{
"content": "The gain of a parabolic dish depends on diameter",
"children": [
{
"content": "A-7-5-11 (B) You want to convert a surplus parabolic dish for amateur radio use, the gain of this antenna depends on:\nA\tthe material composition of the dish\nB\tthe diameter of the antenna in wavelengths\nC\tthe polarization of the feed device illuminating it\nD\tthe focal length of the antenna",
"children": [
{
"content": "> Gain is primarily affected by the antenna aperture (reflector area) to wavelength ratio."
}
]
}
]
}
]
},
{
"content": "ground planes",
"children": [
{
"content": "A-7-7-3 (D) The plane from which ground reflections can be considered to take place, or the effective ground plane for an antenna is:\nA\tas much as 6 cm below ground depending upon soil conditions\nB\tas much as a meter above ground\nC\tat ground level exactly\nD\tseveral centimeters to as much as 2 meters below ground, depending upon soil conditions",
"children": [
{
"content": "> Current penetration around an antenna depends first on frequency and then on soil conductivity and dielectric constant. At HF frequencies over salt water, penetration ranges from 5 to 18 centimetres. Over poor ground, penetration can exceed 10 metres."
}
]
}
]
},
{
"content": "takeoff angle",
"children": [
{
"content": "A-7-7-4 (C) Why is a ground-mounted vertical quarter-wave antenna in reasonably open surroundings better for long distance contacts than a half-wave dipole at a quarter wavelength above ground?\nA\tIt has an omnidirectional characteristic\nB\tIt uses vertical polarization\nC\tThe vertical radiation angle is lower\nD\tThe radiation resistance is lower",
"children": [
{
"content": "> Key words: DIPOLE AT A QUARTER WAVELENGTH HEIGHT. At heights below three eights of a wavelength, ground reflections cause horizontal dipoles to direct more energy straight up. At a height of one half-wavelength, radiation at 90 degrees is minimized and two lobes form at 30 degrees. In this comparison, the ground-mounted vertical undoubtedly exhibits a lower radiation angle as it cannot possibly radiate upwards."
}
]
},
{
"content": "A-7-7-5 (B) When a half-wave dipole antenna is installed **one-half wavelength above ground**, the:\nA\tradiation pattern is unaffected\nB\t**vertical or upward radiation is effectively cancelled**\nC\tradiation pattern changes to produce side lobes at 15 and 50 degrees\nD\tside lobe radiation is cancelled",
"children": [
{
"content": "> At heights below three eights of a wavelength, ground reflections cause horizontal dipoles to direct more energy straight up. At a height of one half-wavelength, radiation at 90 degrees is minimized and two lobes form at 30 degrees."
}
]
},
{
"content": "A-7-7-7 (B) For long distance propagation, the vertical radiation angle of the energy from the antenna should be:\nA\tmore than 30 degrees but less than 45 degrees\nB\tless than 30 degrees\nC\tmore than 45 degrees but less than 90 degrees\nD\t90 degrees",
"children": [
{
"content": "> Depending on band (for example, 10, 15 and 20 metre) and distance, preferred radiation angles range from 1 to 25 degrees for long distance communication. A low radiation angle permits hitting the ionosphere at a greater distance for longer skip distances."
}
]
},
{
"content": "A-7-7-8 (D) Greater distance can be covered with multiple-hop transmissions by decreasing the:\nA\tpower applied to the antenna\nB\tmain height of the antenna\nC\tlength of the antenna\nD\tvertical radiation angle of the antenna",
"children": [
{
"content": "> Depending on band (for example, 10, 15 and 20 metre) and distance, preferred radiation angles range from 1 to 25 degrees for long distance communication. A low radiation angle permits hitting the ionosphere at a greater distance for longer skip distances."
}
]
},
{
"content": "NVIS",
"children": [
{
"content": "A-7-7-11 (D) Which antenna system and operating frequency are most suitable for Near Vertical Incidence (NVIS) communications?\nA\tA horizontal antenna at a height of half a wavelength and an operating frequency at the optimum working frequency\nB\tA vertical antenna and a frequency below the maximum usable frequency\nC\tA vertical antenna and a frequency above the lowest usable frequency\nD\tA horizontal antenna less than 1/4 wavelength above ground and a frequency below the current critical frequency",
"children": [
{
"content": "> Near-Vertical Incidence Sky wave (NVIS) -- \"The use of very low dipole antennas that radiate at very high elevation angles has become popular in emergency communications (\"emcomm\") systems. This works at low frequencies (7 MHz and below) that are lower than the ionosphere's critical frequency -- the highest frequency for which a signal traveling vertically will be reflected.\" (ARRL Handbook, 2012 ed., 21.2.12 NVIS Antennas)"
}
]
}
]
},
{
"content": "A-7-7-1 (C) For a 3-element Yagi antenna with horizontally mounted elements, how does the main lobe takeoff angle vary with height above flat ground?\nA\tIt does not vary with height\nB\tIt depends on E-region height, not antenna height\nC\tIt decreases with increasing height\nD\tIt increases with increasing height",
"children": [
{
"content": "> Greater antenna heights tend to lower the main radiation lobe where ground reflections end up in phase with direct radiation from the antenna."
}
]
},
{
"content": "A-7-7-10 (A) Why can a horizontal antenna closer to ground be advantageous for close range communications on lower HF bands?\nA\tThe ground tends to act as a **reflector**\nB\tLower antenna noise temperature\nC\tLow radiation angle for closer distances\nD\tThe radiation resistance is higher",
"children": [
{
"content": "> Near-Vertical Incidence Sky wave (NVIS) -- \"The use of very low dipole antennas that radiate at very high elevation angles has become popular in emergency communications (\"emcomm\") systems. This works at low frequencies (7 MHz and below) that are lower than the ionosphere's critical frequency -- the highest frequency for which a signal traveling vertically will be reflected.\" (ARRL Handbook, 2012 ed., 21.2.12 NVIS Antennas)"
}
]
}
]
},
{
"content": "ground interactions distort the free-space radiation pattern.",
"children": [
{
"content": "A-7-7-6 (A) How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?\nA\tIf the antenna is less than one-half wavelength high, reflected radio waves from the ground significantly **distort the pattern**\nB\tAntenna height has no effect on the pattern\nC\tIf the antenna is less than one-half wavelength high, radiation off the ends of the wire is eliminated\nD\tIf the antenna is too high, the pattern becomes unpredictable",
"children": [
{
"content": "> Below one half-wavelength in antenna height, there is little point in selecting a given broadside direction: for example, choosing a north-south orientation to favour east-west radiation will not pay significant dividends for antennas close to ground."
}
]
}
]
},
{
"content": "feedpoint impedance",
"children": [
{
"content": "A-7-7-9 (C) The impedance at the centre of a dipole antenna more than 3 wavelengths above ground would be nearest to:\nA\t300 ohms\nB\t600 ohms\nC\t75 ohms\nD\t25 ohms",
"children": [
{
"content": "> The impedance of a dipole in free space is known as 73 ohms. Below a height of a half-wavelength, impedance is greatly affected by ground proximity. At one wavelength and up, impedance begins to track the free-space value more closely."
}
]
}
]
},
{
"content": "radiation resistance",
"children": [
{
"content": "A-7-8-1 (A) What is meant by the radiation resistance of an antenna?\nA\tThe equivalent resistance that would dissipate the same amount of power as that radiated from an antenna\nB\tThe resistance in the atmosphere that an antenna must overcome to be able to radiate a signal\nC\tThe specific impedance of an antenna\nD\tThe combined losses of the antenna elements and transmission line",
"children": [
{
"content": "> The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have \"disappeared\" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100."
}
]
},
{
"content": "A-7-8-2 (A) Why would one need to know the radiation resistance of an antenna?\nA\tTo match impedances for maximum power transfer\nB\tTo measure the near-field radiation density from a transmitting antenna\nC\tTo calculate the front-to-side ratio of the antenna\nD\tTo calculate the front-to-back ratio of the antenna",
"children": [
{
"content": "> The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have \"disappeared\" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100."
}
]
},
{
"content": "A-7-8-3 (C) What factors determine the radiation resistance of an antenna?\nA\tSunspot activity and time of day\nB\tIt is a physical constant and is the same for all antennas\nC\tAntenna location with respect to nearby objects and the conductors length/diameter ratio\nD\tTransmission line length and antenna height",
"children": [
{
"content": "> The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have \"disappeared\" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100."
}
]
},
{
"content": "A-7-8-4 (A) What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?\nA\tAntenna efficiency\nB\tBeamwidth\nC\tEffective Radiated Power\nD\tRadiation conversion loss",
"children": [
{
"content": "> The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have \"disappeared\" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100."
}
]
},
{
"content": "A-7-8-5 (D) What is included in the total resistance of an antenna system?\nA\tRadiation resistance plus transmission resistance\nB\tTransmission line resistance plus radiation resistance\nC\tRadiation resistance plus space impedance\nD\tRadiation resistance plus ohmic resistance",
"children": [
{
"content": "> The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have \"disappeared\" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100."
}
]
},
{
"content": "A-7-8-8 (D) What is the term used for an equivalent resistance which would dissipate the same amount of energy as that radiated from an antenna?\nA\tj factor\nB\tAntenna resistance\nC\tK factor\nD\tRadiation resistance",
"children": [
{
"content": "> The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have \"disappeared\" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100."
}
]
}
]
},
{
"content": "The half-power **beam width** is defined as the angle through which the directivity is fewer than 3 dB down from the peak.",
"children": [
{
"content": "A-7-8-6 (C) How can the approximate beamwidth of a beam antenna be determined?\nA\tMeasure the ratio of the signal strengths of the radiated power lobes from the front and side of the antenna\nB\tMeasure the ratio of the signal strengths of the radiated power lobes from the front and rear of the antenna\nC\tNote the two points where the signal strength is **down 3 dB** from the maximum signal point and compute the angular difference\nD\tDraw two imaginary lines through the ends of the elements and measure the angle between the lines",
"children": [
{
"content": "> Beamwidth is defined as the width in degrees over which the major lobe is within 3 dB of maximum gain, this is equally described as the angle between the half-power points."
}
]
},
{
"content": "A-7-8-9 (B) Antenna beamwidth is the angular distance between:\nA\tthe 3 dB power points on the first minor lobe\nB\tthe points on the major lobe at the half-power points\nC\tthe maximum lobe spread points on the major lobe\nD\tthe 6 dB power points on the major lobe",
"children": [
{
"content": "> Beamwidth is defined as the width in degrees over which the major lobe is within 3 dB of maximum gain, this is equally described as the angle between the half-power points."
}
]
}
]
},
{
"content": "antenna efficiency",
"children": [
{
"content": "A-7-8-7 (D) How is antenna percent efficiency calculated?\nA\t(radiation resistance / transmission resistance) x 100\nB\t(total resistance / radiation resistance) x 100\nC\t(effective radiated power / transmitter output) x 100\nD\t(radiation resistance / total resistance) x 100",
"children": [
{
"content": "> The power delivered to an antenna can be transformed in two ways: some of it is lost through heat and dielectric losses, the rest is radiated. The part that is radiated can be imagined to have \"disappeared\" into a virtual resistance. Radiation Resistance is defined as an equivalent resistance that would have dissipated all the power radiated. The dimensions of the radiating element, particularly its length, and its immediate environment, the proximity to ground for instance, affect radiation resistance. Except for electrically short antennas, radiation resistance makes up most of the antenna impedance. Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100."
}
]
},
{
"content": "A-7-8-10 (C) If the ohmic resistance of a half-wave dipole is 2 ohms, and the radiation resistance is 72 ohms, what is the antenna efficiency?\nA\t72%\nB\t100%\nC\t97.3%\nD\t74%",
"children": [
{
"content": "> Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100. In this example, 72 divided by 74 is 97.3%"
}
]
},
{
"content": "A-7-8-11 (A) If the ohmic resistance of a miniloop antenna is 2 milliohms and the radiation resistance is 50 milliohms, what is the antenna efficiency?\nA\t96.15%\nB\t52%\nC\t25%\nD\t50%",
"children": [
{
"content": "> Antenna efficiency in percentage can be computed as Radiation Resistance over total resistance times 100. In this example, 50 divided by 52 is 96.2%"
}
]
}
]
},
{
"content": "miscellaney",
"children": [
{
"content": "doppler shift is relevant in the context of satellite work",
"children": [
{
"content": "A-7-5-4 (C) On VHF/UHF frequencies, Doppler shift becomes of consequence on which type of communication?\nA\tSimplex line-of-sight contact between hand-held transceivers\nB\tContact with terrestrial mobile stations\nC\tContact via satellite\nD\tContact through a hilltop repeater",
"children": [
{
"content": "> \"Doppler shift: the change in frequency of a received signal due to the motion of the satellite. This requires adjustment of the transmit or receive frequency, with the common practice being to change the higher of the two frequencies in use\" (http://www.amsat.org/). Low Earth orbiting satellites travel at speeds around 28 000 km/h. The higher the operating frequency, the higher the possible shift: for example, +/- 600 Hz on 10 m, +/- 3 kHz on 2 m and +/- 9 kHz on 70 cm."
}
]
}
]
}
]
}
]
}
]