This is my self-made study guide for the Canadian amateur radio license exam, Advanced qualification level. Questions and answers from the pool are here reformatted into statements. Future re-edits are likely. Download latest and greatest version from KY8D.NET/CA. I made this for me, and you get it free. Be aware that it comes with no guarantee. This version is dated July 15, 2022. No rights reserved. {{pause}} The term "back E M F" refers to a voltage that opposes applied E M F. One Time Constant in an R L circuit (as opposed to R C) refers to how long it takes for current to reach 63.2% of maximum. One Time Constant in an R C circuit (as opposed to R L) refers to how long is required for a voltage charge to rise by 63.2% closer to the supply voltage. Likewise for a voltage charge to fall by 63.2% closer toward zero. During a span of two time constants, an R C circuit starting at zero will reach 63.2% in the first time constant. During the second it will continue charging up through 63.2% of the span still remaining. To calculate a two-time-constant result, start with the first time constant's 63.2%, and add to it 63.2% of the remaining span. Answer: 86.5%. If discharging, the charge will fall down through 63.2% and so reach 36.8% during the first time constant. During the second it will continue discharging through 63.2% of the charge still remaining. Thus to solve in reverse, simply subtract from 100% whatever would have been the result if instead charging. 100% minus 86.5% equals 13.5%. To know the duration of an R C time constant as measured in seconds, multiply Farads and Ohms. Thus 100 uF times 470 kilohms give 47 seconds. "Skin Effect" causes RF currents to flow only close to the surface. The more so as frequency increases. At RF, nearly all current flows close the surface. Resistance for the same conductor is higher for RF than for DC, because at RF the center is off-limits. The unit of measure for capacitors is the Farad, for inductors it is the Henry. Surrounding any wire through which current passes will be an electromagnetic field. The Left Hand Rule gives that field's direction. With thumb pointing in the direction of current, fingers indicate the field's direction. The term for energy stored in any kind of field is "potential energy". Between the charged plates of a capacitor is an electrostatic field. The formula for resonance is: 1 over f equals 2 pi times the square root of L C. Calculate resonant frequency for both L C and R L C circuits the same exact way. Series versus parallel makes no difference to resonant frequency. Resistance affects only quality (which is to say bandwidth and damping). So, unless to solving for Q, ignore any value given for R. To solve an R L C for frequency, multiply Henrys by Farads, take the square root, then times that by 2 pi. Lastly invert. To solve an R L C for capacitance, multiply Hertz by 2 pi. Invert and then square. Lastly divide by Henrys. To solve an R L C for inductance, multiply Hertz by 2 pi. Invert and then square. Lastly divide by Farads. Correct answers might be rounded off. Among the wrong answers there may be one which could have been got by a simple calculation mistake. Always check twice. Asked to solve the Q of an R L C, divide Henrys by Farads, take the square root, times it by R inverted. Including a resistor in a parallel resonant circuit decreases Q, increasing the bandwidth. Elements are called "semiconductors" which sometimes exhibit metallic (conducting) characteristics, and other times non-metallic (insulating) characteristics. Two such elements are silicon and germanium. A third is gallium-arsenide, preferred at microwave frequencies. In its pure form, silicon is a good insulator. The addition of small impurities changes it into a semiconductor. This process is called "doping". An N-type semiconductor has been doped to have more free electrons than does a pure crystal. P-type is doped to have instead "electron holes" (meaning a deficit of free electrons). Both types carry a charge, and so are termed "charge carriers". A Zener diode maintains constant voltage under varying current, and so is used to regulate voltage. Zener diodes are rated for power at a given temperature, above which they handle less. The current of a Zener diode at maximum dissipation will be Watts divided by Volts. Structurally, the two main categories of semiconductors are: junction, and point contact. The major ratings for diodes are: maximum forward current; and peak inverse voltage (P I V). A diode whose capacitance varies with voltage is called a varactor. A common use for the hot-carrier (aka "Schottky") diode is as VHF and UHF mixers and detectors. In a junction diode, maximum forward current is limited by junction temperature. A common use for point contact diodes is as an RF detector. A common use for P I N diodes is as an RF switch. Bipolar transistors often see use as amplifiers. Their gain is quantified in terms of alpha and beta. Alpha is a given transistor's ratio of the change in collector current with respect to a change in emitter current, ostensibly its forward gain in common base configuration. Beta is a similar ratio between collector and base currents, forward gain common emitter or common collector configurations. Bipolar transistors can be either NPN or PNP, where N or P denotes the doping of emitter, base, and collector. The NPN type conducts when the base is positive. The PNP type is opposite, conducting when the base is negative. Here's a mnemonic for their schematic symbols: for NPN think "not pointing in"; and for PNP think "pointer inward pointing". On a schematic diagram, the little arrow points like so: from above ground toward ground; or from ground toward negative. A given bipolar transistsor's alpha is equal to its beta divided by the sum of beta plus 1. Going the other way, beta is equal to alpha divided by the difference 1 minus alpha. Thus beta gain in common emitter or common collector configuration is very high as compared to alpha gain for common base configuration. Input and output are in phase for common base and common collector amplifiers. They are 180 degrees out of phase in common emitter amplifiers. The input impedance of common base amplfiers is very low compared to the output impedance. The advantages of a Darlington pair amplifier are high gain, high input impedance, and low output impedance. F E T stands for Field Effect Transistor. An enhancement-mode F E T is off by default (that is to say, it offers no "channel"). Without gate voltage, no current flows. Applying gate voltage enhances the channel. A depletion-mode F E T is on by default (offers a "channel" by default). With no gate voltage, current still flows. Applying gate voltage depletes the channel. Many MOSFET devices have a built-in Zener diode to prevent damage to gate-insulation from small static charges or excessive voltages. Special precautions are necessary in handling F E T and CMOS devices because they are susceptible to damage from static charges. Input impedance is high for an F E T; low for bipolar transistors. The three terminals of an F E T are: source, gate, drain. For an MOSFET, add sometimes also a fourth, the body. Although nearly always, it is internally tied to the source. The two basic types of an F E T are: N-channel and P-channel. The three terminals of a silicon controlled rectifier are: anode, gate, cathode. An SCR is a P N P N type of device, with two stable operating conditions: conducting, and non-conducting. An SCR is a member of the thyristor family. When an SCR is triggered, it behaves like a junction diode. Put another way, an SCR behaves like a forward-biased rectifier when it is gated "on". Its control element is called the gate. In amateur radio equipment, the major application for an SCR is in a power supply overvoltage (aka "crowbar") circuit. Class A amplifiers operate through the full signal cycle, thereby exhibiting the highest linearity and least distortion. Class AB amplifier operate between 180 and 360 degrees. Class B amplifiers operate for 180 degrees. Class C amplifiers operates less than 180 degrees. Highly efficient, they are useful only where linearity is unimportant. Such as in the output stage of a CW, RTTY or FM transmitter. And useful also where linearity is not desired, such as in a mixer. Class C cannot be used for single sideband. In a common source amplifier, input impedance is determined by its gate biasing network, output impedance by the drain resistor. A source-follower circuit is also called "common drain". Comparing F E T against bipolar transistor amplfiers: A common source circuit is similar to common emitter; Common drain similar to common collector; And common gate similar to common base. An operational amplifier (op-amp) is a high-gain, direct-coupled differential amplifier whose characteristics are determined by components mounted externally. Characteristics of the ideal op-amp are infinite input impedance, zero output impedance, infinite gain, and flat frequency response. The gain of a closed-loop op-amp circuit is determined by its external feedback network. An op-amp's offset voltage is the potential between its input terminals in a closed-loop condition. The advantage of using an op-amp instead of L C elements in an audio filter is that op-amps exhibit gain rather than insertion loss. A principal use of op-amp R C active filters are as audio filters for receivers. A "mixer" circuit combines two signals, obtaining (along with the original two) their sum and difference frequencies. That stage in a transmitter which would change a 5.3 MHz input signal to 14.3 MHz is the mixer. When an excessive amount of signal energy reaches the mixer circuit, spurious signals are generated. A circuit tuned to resonate at a frequency higher than that applied is a frequency multiplier. In a frequency multiplier, the input signal is coupled to the base of a transistor through a DC blocking capacitor. A frequency multiplier must be operated in class C. In a frequency multiplier, 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 variable capacitor (C2) tunes L1 to the desired harmonic, the pair operating in conjunction as a frequency multiplier. The fixed capacitor (C3) is a RF by-pass capacitor providing an RF ground at the VCC connection point of L1. An AND-gate puts out "1" only when all inputs are "1". A NAND does the opposite, putting out "0" only when all inputs are "1". An OR gate puts out "1" when any input is "1". A NOR gate does the opposite, putting out "0" when any input is "1". An EXCLUSIVE OR gate puts out "1" when only a single input is "1". An EXCLUSIVE NOR gate does the opposite, putting out "0" when only a single input is "1". A NOT gate (also known as an Inverter) puts out "0" for "1", and "1" for "0". A flip-flop circuit is a binary sequential logic element with two stable states A latch is a flip-flop. So is a bistable multivibrator. In a multivibrator circuit, when one transistor conducts, the other is cut off. A crystal lattice filter is a filter with narrow bandwidth and steep skirts, made using quartz crystals. The bandwidth and response shape of a crystal lattice filter is determined by the relative frequencies of the individual crystals. For single-sideband phone emissions, the bandwidth of a good crystal lattice filter would be 2.4 kHz. The main advantage of a crystal oscillator over a tuned LC oscillator is much greater frequency stability. A quartz crystal filter is superior to an LC filter for narrow bandpass applications because of the crystal's high Q . Piezoelectricity is generated by deforming certain crystals. Electrically, a crystal looks like a very high Q tuned circuit. A crystal circuit which has an output close to an integral multiple of the crystal frequency is called an overtone oscillator. High power output does not apply to a crystal when used in an oscillator circuit. Crystal oscillators, filters and microphones depend upon the principle of piezoelectric effect. Crystals are not applicable to active filters. The three general groupings of filters are: high-pass, low-pass and band-pass. Butterworth filters have maximally flat response over their pass-band. Chebyshev filters have steeper skirts but allow ripple in their passband. Resonant cavities are used as narrow bandpass filters at VHF and higher frequencies. A 1/4 wavelength coaxial cavity for 50 MHz would be 6 meters divided by 4, or 1.5 meters. Cavity filters are not suitable for use at audio and low radio frequencies for being stupendously huge. Helical resonators, when installed in a VHF or UHF receiver's front end, help with receiver overload and spurious responses. The easiest amplitude dimension of a pure sine to measure via oscilloscope is its peak-to-peak voltage. RMS voltage is 0.707 of the peak. An RMS value of AC voltage will heat a resistor identically to DC volts of identical magnitude. In applying Ohm's law to AC circuits, use RMS. Multiply the peaks of AC current and or voltage each by 0.707. AC voltmeter scales are usually calibrated to read RMS, which is to say the effective value. Peak Envelope Power (P.E.P.) is measured at the modulation envelope's highest crest. Calculate P E P for S S B as Peak Envelope Voltage (P E V) multiplied by 0.707. That value squared. Then divide by the load resistance. Calculate the power output of a transmitter via Ohm's Law. Given voltage and load resistance, square the voltage then divide by resistance. Say you want the Peak Envelope Power as seen by a dummy load. Obtain Peak Envelope Voltage via oscilloscope. Multiply it by 0.707 to have RMS. Then employ the standard power calculation. Tricky wording might call out an "average-reading" power meter. Calculate it even so as RMS. A dip meter is a variable frequency oscillator with metered feedback current. What a dip meter does is give an indication of the resonant frequency of a circuit. It works by supplying the RF energy which enables you to check resonant frequencies. Use one to measure resonance in antenna traps and tuned circuits. A dip meter may not be used directly to measure the value of capacitance or inductance. A dip meter should be loosely coupled to the circuit under test. The dip meter is most directly applicable to parallel tuned circuits. Transmitter power output is not a factor affecting the frequency accuracy of a dip meter. The dial calibration on the output attenuator of a signal generator reads accurately only when the attenuator is properly terminated. A signal generator is a high-stability oscillator which can produce a wide range of frequencies and amplitudes. The two instruments needed to measure FM receiver sensitivity for a 12 dB SINAD ratio (signal + noise + distortion over noise + distortion) are: calibrated RF signal generator with FM tone modulation, and also a total harmonic distortion (THD) analyzer. Factors limiting the accuracy, frequency response and stability of a frequency counter are the speed of the logic, its time base accuracy, and time base stability. The frequency counter's accuracy can be improved by increasing the accuracy of the time base. Given a frequency counter whose time base accuracy is plus-or-minus 0.1 PPM, divide its readout by 10 million to learn the maximum error. Suppose instead the frequency counter's time base accuracy were 10 PPM, divide its reading by 100,000 to get the maximum error. Frequency counters normally use a crystal oscillator for their clock. A frequency counter's accuracy is determined by its timebase generator. A frequency-marker generator relies on a stable low-frequency oscillator, with harmonic output, to facilitate the calibration of receiver dial settings. The traditional way of verifying the accuracy of a crystal calibrator is to zero-beat the crystal oscillator against a standard frequency station such as WWV. A voltage-controlled crystal oscillator is not, by itself, considered a high-stability reference. Say you want to calibrate your station frequency reference to the WWV on your receiver. The resulting beat tone must be of a frequency as low as possible and with a period as long as possible. Say you feed 100 Hz into the horizontal input of an oscilloscope and a 150 Hz into the vertical input. The Lissajous pattern you'll see will have 3 horizontal loops and 2 vertical loops. This is because acommon factor between 100 and 150 is 50. Thus 2 times 50 for one, and 3 times 50 for the other. Therefor you see 2 loops one way, and 3 loops the other. Each set of loops showing on its opposite axis. An oscilloscope's accuracy is limited by the accuracy of its time base, plus the linearity and bandwidth of its deflection amplifiers. An oscilloscope's frequency response can be improved by increasing the horizontal sweep rate, and the vertical amplifier's frequency response. A dual-trace oscilloscope can display the input and output of a circuit both at the same time. An oscilloscope cannot be used to determine FM carrier deviation directly. An oscilloscope's bandwidth is the highest frequency signal it can display. A Lissajous figure showing as a diagonal straight line indicates a phase of zero or 180 degrees. Picture a Lissajous pattern showing 5 loops vertically and 2 loops horizontally. Frequency at the X input is 100 kHz, while frequency at the Y input is unknown. Those 5 loops on the X axis inform that 5 is a common factor between X and Y. And 100 kHz divided by 5 is 20kHz. Seeing 2 loops on the Y you determin F by multiplying. Thus 20 kHz times 2 solves for the unknown. An oscilloscope probe must be compensated every time the probe is used with a different oscilloscope. An oscilloscope is the best instrument for checking the signal quality of a CW or single-sideband transmitter. A sampling device to feed a portion of transmitter's RF output to the vertical input of an oscilloscope is the best way to check its signal quality. An amp meter's range can be extended by adding resistance in parallel with the meter. This is called shunting. Say you have an moving-coil meter having 96 Ohms internal resistance which passes 40 microamperes at full scale. Needed is a shunt resistor to change its full scale to 1 mA. Ohm's Law gives the potential as 3.84 milivolts. Subtraction gives the shunt current: 960 microamperes. Ohm's Law solves the shunt resistor needed as 3.84 milivolts over 960 microamperes which works out to 4 Ohms Another moving-coil meter passes 1 milliamp through 0.5 Ohms internal resistance. You want it to serve as a voltmeter having 20 volts at full scale. Ohm's Law gives the existing potential as 500 microvolts. That leaves 19.9995 volts potential to be divided accross the add-on series resistor. Dividing that value by 1 milliamp gives the resistance needed: 19,999.5 Ohms. Say a voltmeter's range is 150 volts with 150,000 Ohms internal resistance. You want to rescale it for 750 volts. Ohm's Law gives the existing current as 1 mA. The needed multiplier resistor must pass 1 mA while dividing 600 volts across itself. Ohm's Law gives the resistance you want as 600,000 Ohms. The sensitivity of an ammeter is the magnitude of current which gives a full-scale deflection. Say a voltmeter lists its sensitivity at 20 kilohms per volt. Ohm's Law informs that it passes 50 microamperes at full scale. Another voltmeter has 150,000 Ohms of resistance on its 150 Volt range. Ohm's Law shows the meter as having 1,000 Ohms per Volt. Inside of a multimeter, when you switch from a lower voltage range to a higher, resistance is added in series. For best accuracy, connect an RF wattmeter at the transmitter's output connector. The line impedance of most RF wattmeters is 50 ohms. A bridge rectifier has the highest average output voltage. In a half-wave power supply with a capacitor input filter and a load drawing little or no current, the peak inverse voltage across the diode can reach 2.8 times RMS. In a full-wave centre-tap power supply the peak inverse voltage will always be 2.8 times RMS. A full-wave bridge rectifier does not require a centre-tapped secondary on the transformer. A full-wave bridge rectifier, as compared to a centre-tap rectifier, gives double the output voltage. With a full-wave power supply, output ripple frequency is twice that of the AC input. With a half-wave power supply, output ripple frequency is half that of the AC input. Full-wave voltage doublers use both halves of an AC wave. The two major ratings that must not be exceeded for silicon-diode rectifiers are: peak inverse voltage; average forward current. In a high voltage power supply, a resistor and capacitor should be wired in parallel with the power-supply rectifier diodes so as to equalize voltage drops and guard against transient voltage spikes. The output waveform of an unfiltered full-wave rectifier connected to a resistive load is a series of pulses at twice the frequency of the AC input The two types of filters in general use for power supplies are: choke-input, and capacitor-input. The advantage of the capacitor input over the choke input is: higher terminal voltage output. With a normal load, the choke input filter will give the best regulated output. Filter chokes are rated according to inductance and current-handling capacity. A secondary function of the bleeder resistor in a power supply is to: improve voltage regulation. In a power supply, series chokes will readily pass the DC but will impede the flow of the AC component. With choke input filters, include a bleeder resistor so that a needful minimum current is drawn all the time. In a power supply, excessively high rectifier peak current and peak inverse voltages can be caused by the filter forming a series resonant circuit with the first choke and first capacitor. So in designing a power supply, be careful of resonance effects lest ripple voltage build up to a high value. Select very carefully the first choke and first capacitor. In designing a choke input filter power supply, it is advisable to use capacitors rated at the peak transformer voltage. This is a safety precaution against a burned out bleeder, since then voltages could reach the peak transformer voltage. In a linear electronic voltage regulator, the conduction of a control element is varied in direct proportion to the line voltage or load current. In a switching voltage regulator, the control device is switched on and off, with the duty cycle proportional to the line or load conditions. Typically, a Zener diode is used as the stable reference voltage in a linear voltage regulator. A series and shunt voltage regulators differ in how they connect to the load, whether upstream in series, or else in parallel with a resistor upstream in series. Series voltage regulators offer efficient utilization of power. Shunt voltage regulators instead present constant load to the voltage source. In a linear voltage regulator, remote sensing is accomplished via a feedback connection to an error amplifier made directly to the load. A three-terminal regulator contains a voltage reference, error amplifier, sensing resistors and transistors, and a pass element. A three-terminal regulator may also feature a reference, high-gain amplifier, temperature-compensated voltage-sensing resistors and transistors. In addition to an input voltage range, further important characteristics of a three terminal regulator are: output voltage and maximum output current. There are two main categories of closed-loop-control electronic regulators: linear and switching. In a series-regulated power supply, the power dissipation of the pass transistor is directly proportional to the load current and the input/output voltage differential. In any regulated power supply, the output is cleanest and the regulation is best at the point where the sampling network or error amplifier is connected. In a power supply, the output voltage divided by total current (through the bleeder resistor) is its load resistance. The regulation of long-term changes in the load resistance of a power supply is called: static regulation. The regulation of short-term changes is dynamic regulation. The dynamic regulation of a power supply is improved by increasing the value of the output capacitor. A power supply filter will give better dynamic regulation if: the output capacitance is increased. In a power supply, four diodes connected together in a BRIDGE act as a rectifier. In a power supply, components located both at the input before the transformer and also before the output are: fuses. In a regulated power supply, the electrolytic filter capacitor's output connects to the: voltage regulator. A diode across the input and output terminals protects it from reverse voltages. In a Hartley oscillator, feedback is coupled through a tapped coil. In a Pierce oscillator, feedback is supplied through coupling via a single capacitor in series with the crystal. In a Colpitts oscillator, feedback is coupled through a capacitive divider. A Colpitts oscillator is commonly used in a VFO because it is stable. A very stable reference oscillator must be used as part of a phase-locked loop frequency synthesizer because any phase variations will produce phase noise in the synthesizer output. In an RF oscillator circuit designed for high stability where feedback is drawn from two capacitors connected in series, silver mica capacitors are the best choice. A circuit depending on positive feedback for its operation would be: an oscillator. An apparatus with an oscillator and a class C amplifier would be: a two-stage CW transmitter. Adjustable pi network tuning controls on a power amplifier allow efficient transfer of power to the antenna. The purpose of using a centre-tap on a transmitting tube's filament transformer is to prevent modulation by the filament's AC supply. In a grounded grid amplifier: the input signal is applied to the cathode; the plate is connected to the pi-network through a blocking capacitor; the plate's RF chocke connects to high voltage; the cathode's RF choke connects to bias; the secondary winding of a transformer provides filament voltage directly; each side of the filament connects to a grounded by-pass capacitor. The approximate voltage required for an output of 400 watts at 400 milliamps with 50% efficiency would be 2000 volts. This according to Ohm's Law, since 400 milliamps at 400 watts requires 1000 volts and efficiency is 50%. After making internal tuning adjustments to a power amplifier, before you turn it on again, first ensure that all shielding is fastened in place. Harmonics produced in an early stage of a transmitter may be reduced in a later stage by tuned circuit coupling between stages. In a simple two-stage CW transmitter circuit, the oscillator stage and the class C amplifier stage are inductively coupled by an RF transformer. Another role of the RF transformer is to be part of a tuned circuit. 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 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 form a low-pass filter. In a simple 2 stage CW transmitter, the transistor in the second stage would act as a power amplifier. An advantage of keying the buffer stage in a transmitter is that changes in oscillator frequency are less likely. A neutralizing circuit in an RF amplifier cancels the effects of positive feedback. The reason for neutralizing the final amplifier stage of a transmitter is to eliminate parasitic oscillations. Parasitic oscillations are usually generated due to accidental resonant frequencies in the power amplifier. Parasitic oscillations would tend to occur mostly in RF power output stages. Neutralization is necessary for some vacuum-tube amplifiers to cancel oscillation caused by the effects of inter-electrode capacitance. Parasitic oscillations in an RF power amplifier may be caused by lack of neutralization. As a power amplifier is tuned, best neutralization is indicated by minimal change on the grid current meter as the output circuit is changed. A balanced modulator produces double sideband, suppressed carrier. A single-sideband phone signal can be produced by using a balanced modulator followed by a filter. Carrier suppression in a single-sideband transmitter takes place in the balanced modulator stage. Transmission with SSB, as compared to conventional AM transmission, results in 6 dB gain in the transmitter and 3 dB gain in the receiver. The peak power output of a single-sideband transmitter, when being tested by a two-tone generator is twice the RF power output of any of the tones. A single sideband transmitter's linearity is measured by a two-tone test. Any two tones within its passband that aren't harmonically related are input via the microphone and viewed on an oscilloscope. If linearity is good they will not mix, such that sum and difference frequencies are not produced. In a single-sideband transmission the carrier is suppressed at least 40 dB. Flat-topping in a transmission is signal distortion caused by excessive drive. The amplifier tries to create peaks above the voltage supplied. On reaching that limit, their tops flatten out. The modulation index of an FM signal is the ratio of frequency deviation over the modulating frequency. If respectively these are 3 kHz and 1 kHz, then the index is 3. An FM transmitter's center frequency is that of its unmodulated carrier. The amount of FM frequency deviation is determined solely by the modulating frequency's amplitude. Any FM wave with single-tone modulation has an infinite number of sideband frequencies. Some types of deviation meters work on the principle of a carrier null and multiplying the modulation frequency by the modulation index. When using some deviation meters, it is important to know the modulating frequency and the modulation index. The "significant bandwidth" (aka large bandwidth) of an FM phone transmission is double the sum of its plus-and-minus deviation and its modulating frequency. Given an example of 5 kHz plus-and-minus deviation and a 3 kHz modulating frequency, the sum is 8 kHz. Hence "significant bandwidth" is 16 kHz. Here comes a tricky one. The raw question is... What is the frequency deviation for a 12.21 MHz reactance-modulated oscillator in a plus-and-minus 5 kHz deviation, 146.52 MHz FM transmitter? So what's that about? Important here is the ratio of 146.52 over 12.21, which is 12-to-1. That is the factor of frequency multiplication. Now knowing that, simply divide the 5 kHz of output deviation by 12. This gives yout 416.7 Hz as the deviation occurring at the reactance-modulated oscillator. When the signals of two transmitters mix together such that sum and difference frequencies are radiated, this is called: intermodulation interference. Intermodulation interference between two repeater transmitters usually occurs when they are in close proximity and the signals mix in one or both of their final amplifiers. Intermodulation interference between two repeaters can often be solved by installing a terminated circulator or ferrite isolator in the transmission line to the transmitter and duplexer. Info from KY8D: Isolators and circulators are multi-port devices having uniquely pre-magnetized ferrite cores. Signals flow unattenuated only in a single direction. Isolators oppose the flow of opposing signals. Circulators pass signals on to the next port in succession, always in a single direction. The next question calls for some math. Here goes. 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? Solve it by doubling one and subtracting the other. 2 times 146.52 minus 146.7 equals 147.34 That's one likely culprit. Now for the other. 2 times 147.6 minus 146.52 equals 146.61 And now you have both. A phase modulator varies the tuning of an amplifier tank circuit to produce FM signals. A pre-emphasis network shapes audio at an FM transmitter to attenuate the lower audio frequencies. A cavity filter is the best type to use in a 2-metre repeater duplexer. Pre-emphasis is the chief difference between phase and frequency modulators. In modern FM transmitters, better sound is produced by a compressor and a clipper placed between the audio amplifier and the modulator. Three important parameters to be verified in an FM transmitter are: power; frequency deviation; and frequency stability. Intermodulation interference products are not typically associated with the I F stage. It is Automatic Level ControlCommon which maintains a relatively constant level of peak RF output in SSB transmitters. Automatic Level ControlCommon is another name for RF compression. Speech compression affords full amplification of low level signals while reducing or eliminating amplification of high level signals. Aliasing amplifiers don't exist, so are not a function included in a digital signal processor. 8 bits are required to provide 256 discrete levels, a ratio of 256:1. Adding one bit to the word length, is equivalent to adding 3 dB to the dynamic range of the digitizer. Digital signal processors employ an analog to digital converter, a mathematical transform, a digital to analog converter, plus a low pass filter. The undesirable result of AF clipping in a speech processor is increased harmonic distortion. In building a speech processor, as compared to AF clipping, RF clipping is difficult to implement. The digital code consists of elements having unequal length is Varicode. According to the Open Systems Interconnection (OSI) model, the base layer involving the interconnection of a packet radio TNC to a computer terminal is: the physical layer. The purpose of a Cyclic Redundancy Check is error detection. One advantage of ASCII over bow-doh code is having both upper and lower case characters. In AMTOR ARQ (Automatic Repeat Query, Mode A) error correction consists of the receiving station automatically requesting repeats when needed. In AMTOR FEC (Forward Error Correction, Mode B), error correction consists of sending each character twice. APRS (Automatic Packet Reporting System) does NOT support automatic link establishment. A hash function algorithm may be used to create a Cyclic Redundancy Check (CRC). The designator AX.25 is associated with the "packet" radio mode. Bow-doh code has 5 information bits. The ISO-8859 extension to the ASCII code has 8 information bits. "Spread spectrum communication" describes a wide-band communications system in which the RF carrier varies according to some predetermined sequence. In spread spectrum communications, a system where the carrier is changed many times per second in accordance with a pseudorandom list of channels is termed "frequency hopping". In spread spectrum communications, the system in which a very fast binary bit stream is used to shift the phase of an RF carrier is termed "direct sequence". Direct sequence and frequency hopping are systems used with "spread spectrum" transmission. The type of signal is used to produce a predetermined alteration in the carrier for spread spectrum communication is a pseudo-random sequence. It difficult to monitor a spread spectrum transmission because your receiver must be frequencysynchronized to the transmitter. Frequency hopping spread spectrum is where the carrier frequency is changed in accordance with a pseudo-random list of channels. Direct-sequence spread spectrum is where the carrier is phase-shifted by a fast binary bit stream. Spread-spectrum signals so resistant to interference because signals not using the spectrum-spreading algorithm are suppressed in the receiver. The spread-spectrum technique of frequency hopping works by the frequency of an RF carrier is changed very rapidly according to a particular pseudo-random sequence. The advantages of the frequency conversion process in a superheterodyne receiver are increased selectivity and optimal tuned circuit design. Factors that should be considered when selecting an intermediate frequency are: image rejection; and responses to unwanted signals. A great advantage of the double-conversion receiver is that it provides greater reduction of image interference for a given front end selectivity. In a communications receiver, a crystal filter would be located in the detector. A multiple conversion superheterodyne receiver is more susceptible to spurious responses than a single-conversion receiver because of the additional oscillators and mixing frequencies involved in the design. In a dual-conversion superheterodyne receiver the respective aims of the first and second conversion stages are image rejection and selectivity. The detector stage of a receiver is where input and output circuits are tuned to the received frequency. The mixer stage of a superheterodyne receiver lies between a tuneable stage and a fixed tuned stage. Say that a single conversion receiver with a 9 MHz I F has a local oscillator operating at 16 MHz. The frequency it is tuned to would be 7 MHz because 16 minus 9 equals 7. A double conversion receiver designed for SSB reception has a beat frequency oscillator and two I F stages with two local oscillators. The advantage of a double over single-conversion receiver is that it suffers less from image interference for a given sensitivity. The mixer stage of a superheterodyne receiver is used to change the frequency of the incoming signal to that of the I F. A superheterodyne receiver designed for SSB reception must have a beat-frequency oscillator to replace the suppressed carrier for detection. The first mixer in a receiver mixes the incoming signal with the local oscillator to produce an intermediate frequency. If the incoming signal to the mixer is 3,600 kHz and the first I F is 9 MHz, the frequency on which the local oscillator operates is 5,400 kHz. Subtract the incoming from the I F. The oscillators in a superheterodyne receiver must be stable and spectrally pure. In a superheterodyne receiver, a stage before the I F amplifier has a variable capacitor for tuning of the local oscillator. 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 tuning the receiver preselector to the reception frequency. In a receiver, the mixer stage combines incoming signals with an oscillator signal to produce the intermediate frequency. Two stages in a superheterodyne receiver that have input tuned circuits tuned to the same frequency are: RF and first mixer. The mixer stage of a superheterodyne receiver demodulates SSB signals. The noise floor of a receiver means the weakest signal that can be detected above the receiver internal noise. A purpose of the first I F amplifier stage in a receiver is to improve selectivity and gain. The amount of gain that should be used in the RF amplifier stage of a receiver that suffices to allow weak signals to overcome noise generated in the first mixer stage. The primary purpose of an RF amplifier in a receiver is to improve the receiver noise figure. Receiver sensitivity is often expressed for UHF FM receivers is RF level for 12 dB SINAD. 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) is: dynamic range. The lower the receiver noise figure becomes, the greater will be the receiver's sensitivity. The noise generated in a receiver of good design originates in the RF amplifier and mixer. Very low noise figures are relatively unimportant for a high frequency receiver because external HF noise, man-made and natural, are higher than the internal noise generated by the receiver. The term which relates specifically to the amplitude levels of multiple signals that can be accommodated during reception is called: dynamic range. 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: preselector. A "de-emphasis network" is an audio shaping network added to an FM receiver to restore proportionally attenuated lower audio frequencies. A product detector mixes an incoming signal with a locally generated carrier. Distortion in a receiver that only affects strong signals usually indicates a defect in or mis-adjustment of the: automatic gain control. In a superheterodyne receiver with AGC, as the strength of the signal increases, the AGC: reduces the receiver gain. The amplified I F signal is applied to the "detector" stage in a superheterodyne receiver:. The low-level output of a detector is: applied to the AF amplifier. 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: automatic gain control. AGC voltage is applied to the: RF and I F amplifiers. AGC is derived in a receiver from one of two circuits. Depending on the method used, it is called: I F derived or audio derived. The two variables which primarily determine the behaviour of an AGC loop are the threshold and decay time. A product detector circuit combines signals from an I F amplifier stage and a beat-frequency oscillator, to produce an audio signal. The part of a superheterodyne receiver which determines the image rejection ratio of the receiver is the RF amplifier pre-selector. The term for the reduction in receiver sensitivity caused by a strong signal near the received frequency is "desensitization". Receiver desensitization is caused by strong near-frequency signals. One way that receiver desensitization can be reduced is by using a cavity filter. Intermodulation in an electronic circuit is caused by nonlinear circuits or devices. An important reason for using a VHF intermediate frequency in an HF receiver is to move the image response far away from the filter passband. Intermodulation interference is produced by the mixing of two or more signals in the front-end of a superheterodyne receiver. Dial display accuracy is not a direct cause of instability in a receiver. Poor frequency stability in a receiver usually originates in the: local oscillator and power supply. Poor dynamic range of a receiver can, in the presence of a strong signal, directly cause desensitization, inter- and cross-modulation. Not feedback, however. A good measurement indicator of VHF receiver performance in an environment of strong out-of-band signals is two-tone third-trder IMD dynamic range, 10 MHz spacing. "Transformer" type and Pi-type antenna tuners are not the same thing at all. Nor are "Series" type and Pi-type antenna tuners the same. "L" type antenna tuners are not suitable for matching to a ground plane antenna. Note from KY8D: this is not strictly true. Any one-way transformer can be reversed for use in the counter-normal direction. A pi-network consists of one inductor and two capacitors or two inductors and one capacitor. A Pi-network offers the greatest transformation ratio among the four offered (since T-network is not in the list). An L-network is of limited utility in impedance matching because it matches only a small impedance range. Note from KY8D: true enough, as compared to a Pi or T network, but only for identical component values. L networks, though, exhibit lower loss. A network transforms one impedance to another by cancelling the reactive part and changing the resistive part. The advantage of a pi-L over a pi network is greater harmonic suppression. Of four networks listed, Pi-L provides the greatest harmonic suppression. A Smith Chart is useful because it simplifies mathematical operations. A quarter wavelength transmission line, when its far end is shorted, presents very low impedance; when open, very high impedance. A transmission line's "Velocity Factor" is expresed as a ratio to the speed of light. Which is to say, the ratio of propagation in the transmission line to propagation in free space. It is determined by dielectrics in the line, calculated as the reciprocal of the square root of the dielectric constant of the separating material. A typical velocity factor for coaxial cable with polyethylene dielectric is 0.66. The physical length of a coaxial cable is shorter than its electrical length because RF energy moves slower along the coaxial cable. A "T Match" is where high-impedance (balanced) transmission line is matched to a lower impedance antenna by meeting the driven element in two places, these spaced a fraction of a wavelength on each side. A "Gamma Match" is where an unbalanced feed system meets the driven element of an antenna at the centre and a fraction of a wavelength to one side. A "Stub Match" is where a short section of transmission line perpendicular to both the antenna and the feedline, matching one to the other. Given a velocity factor of 0.66 and a frequency of 14.1 MHz, the physical length of a typical coaxial stub that is electrically one quarter wavelength long, calculate as 300 divided by 14.1 divided by 4 times 0.66. Therefor 3.51 metres. A coaxial transmission line connects to the driven element of an antenna, co-ax braid at its middle, centre conductor off to one side. Regardless of any variable capacitor or other mechanical arrangements, this still constitutes a "gamma match". Asked to calculate a quarter-wave stub for co-ax of velocity factor 0.8 at 15 MHz, divide 300 first by 15 then by 4 and times that by 0.8 to get 4 meters length. The matching of a driven element with a single adjustable mechanical and capacitive arrangement is descriptive of a "gamma" match. A Yagi antenna uses a gamma match. The adjustable gamma rod connects to the variable capacitor. A Yagi antenna uses a gamma match. The variable capacitor connects to the adjustable gamma rod. A half-wave dipole antenna is normally fed at the point where current is maximum. At the ends of a half-wave dipole, voltage is high and current is low. The impedance of a half-wave antenna at its centre is low, because at this point voltage is low and current is high. Circularly polarized electromagnetic waves have a rotating electric field. Crossed dipoles fed 90 degrees out of phase have circular polarization. Doppler shift is of consequence in satellite communication. For VHF and UHF signals over a fixed path, antennas cross-polarized to each other suffer mutual loss of 20 dB or more. Regarding parabolic dish illumination, among the supplied list of arrangements, "Newtonian" is invalid. A parabolic antenna is very efficient because all the received energy is focused upon the pick-up antenna. Keep parabolic reflector surface error below 0.1 lambda. The gain of a parabolic antenna depends on its diameter in wavelengths. As SWR rises, so does the loss in the transmission line, it being caused by dielectric and conductor heat losses. If a 3 dBd gain antenna is replaced with a 9 dBd gain antenna, ERP will quadruple. This because 9 minus 3 is 6 dB. ERP (Effective Radiated Power) s transmitter output, minus line losses, plus antenna gain in dBd. 1 dB represents a gain or loss of 20%. So, given transmitter output of 125 Watts, combined losses of 1 dB, and antenna gain of 10 dBd, you first get the loss by multiplying 125 by 0.8 to get 100 Watts. Then after applying 10 dB gain, ERP is 1000 Watts. Given transmitter output of 2000 Watts, combined losses of 1 dB, and antnna gain of 10 dBD, alternately, you could just subtract one from 10 to get 9 dB, and so the double 2000 three times in succession for 16,000 Watts. And again, given transmitter output of 1000 Watts P.E.P., composit losses of 1 dB, and antenna gain of 10 dBd, ERP is 8000 Watts. This because 1000 times 0.8 is 800, and 10 dB is a ten-fold increase. A horizontally mounted Yagi antenna's take-off angle is steep when close to the ground, that angle decreasing toward horizontal the higher it's mounted. Comment by KY8D: Simple horizontal antennas, when close to the ground, have a single very fat lobe aimed straight up. Raised somewhat higher, that single lobe begins to grow a dimple in from its summit. Higher yet, that dimple deepens, splitting the original fat lobe into a pair of narrower lobes. It's a gradual process until, at one half wavelength of elevation, the two are now wholly separate, aimed well away from each other. Not quite horizonal, but pretty close. If raised higher still, the process continues. A third lobe developes. It starts as a pimple, then grows fat. In turn, it too grows a dimple and splits. And so forth and so on until, at infinite height, a great many very thin lobes encircle the wire. But for every two lobes, there will be also a deep, sharp null in between. Which is what makes the half-wavelength elevation ideal for DX. There you get a pair of semi-fat lobes bent toward opposing horizons with the one and only null aimed straight up. Now, back to Q and A statements. The plane from which ground reflections take place, the effective ground plane, is conductive soil. This ranging in depth from as little as several centimeters to as much as two meters. All depending upon soil conditions and the frequency itself. A ground-mounted vertical quarter-wave antenna in open surroundings has a low take-off angle. A half-wave dipole just only a quarter wave off the ground suffers from a high take-off angle. Clearly then, the first would serve better for long distance contacts. When a half-wave dipole antenna is installed one-half wavelength above ground, vertical radiation is cancelled. Now a question bizarrely worded. "How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?" To be answered as, "If the antenna is less than one-half wavelength high, reflected radio waves from the ground significantly distort the pattern." Which answer is true. But take note: said distortion is chiefly in the pattern's elevation cross-section. Also some in the azimuthal, just not as much. For long distance propagation, the vertical radiation angle of the antenna should be less than 30 degrees. Greater distance can be covered with multiple-hop transmissions by decreasing the vertical radiation angle of the antenna. The impedance of a half-wave dipole antenna at infinite height is 73 Ohms. Just only three wavelengths approximates that closely enough to not greatly differ. A horizontal antenna closer to ground can be advantageous for close range communications on lower HF bands because the ground tends to act as a reflector. As for the question, "Which antenna system and operating frequency are most suitable for Near Vertical Incidence (NVIS) communications?", note that the S in NVIS stands for "skywave". Therefor answer, "A horizontal antenna less than 1/4 wavelength above ground and a frequency below the current critical frequency." The radiation resistance of an antenna compares it to an equivalent resistor. But rather than dissipated as heat, power is radiated away. One needs to know the radiation resistance of an antenna so as to match impedances for maximum power transfer. Factors determining the radiation resistance of an antenna are its location with respect to nearby objects and the conductors length versus diameter ratio. Included in the total resistance of an antenna system is radiation resistance plus ohmic resistance. Antenna efficiency is the ratio of its radiation resistance to the total resistance of the system. Calculate it as radiation resistance divided by total resistance times 100. Example 1: Say that a dipole's ohmic resistance is 2 ohms, and radiation resistance is 72 ohms. Calculate efficiency as 72 divided by the sum of 72 and 2 for a result of 97.3%. Example 2: Say you have a miniloop with 2 milliohms at DC, and a radiation resistance is 50 milliohms. Calculate its efficiency as 50 divided by the sum of 50 plus two for 96.15%. Antenna beamwidth is the angle between the major lobe's half-power points,the two points which are 3 dB down from maximum gain. A section of waveguide operates like a high-pass filter. Waveguides offer very low loss compared to coaxial cable. But to transfer energy, need to be at least one half wavelength in cross section. And so are typically used at 3GHz and above. Stripline is a printed circuit transmission line. A "micro-stripline" is the same thing only quite small. Compared with coaxial cable, microstripline has poorer shielding. Precautions should you take before beginning repairs on a microwave feed horn or waveguide are to ensure the transmitter is turned off and the power source is disconnected. This study guide was compiled ad-hoc by yours truly, KY8D. I made this for me, and you got it free. Remember it came with no guarantee. No rights reserved. Do with it whatever you please.