G4 Amateur Radio Practices

B. To reduce interference from carriers in the receiver passband

A notch filter removes a very narrow slice of frequencies inside the receiver passband. Tuned to a steady carrier, such as a whistle from a station tuning up or a carrier beating against your signal, it removes that tone while leaving the rest of the wanted signal largely intact; many transceivers can find and track the tone automatically.

• A. A notch filter on an HF transceiver works on received signals; the transmitted voice bandwidth is set by the transmitter's own filtering.
• C. Impulse noise, such as ignition pops, is handled by a noise blanker, which mutes the receiver during each pulse; a notch removes steady tones.
• D. Splatter from an adjacent signal is broadband distortion spread across many frequencies, which a narrow notch cannot remove.

C. It may be possible to reduce or eliminate interference from other signals

To make CW audible, the receiver beats the signal against a local oscillator on one side of it. Switching to the opposite sideband (CW reverse) moves that oscillator to the other side, so an interfering signal close to the wanted one changes to a different pitch and may fall outside the receive filter, while the wanted signal keeps its pitch.

• A. Sideband selection does not affect impulse noise, which is spread across a wide range of frequencies; a noise blanker is the tool for that.
• B. Reversing the sideband changes how you hear signals, not how many stations fit in a passband; station spacing is set by the transmitted signals.
• D. Receiving on the opposite sideband does not change where you transmit, so it cannot prevent out-of-band operation.

C. By reducing receiver gain during a noise pulse

A noise blanker detects short, strong pulses such as ignition noise or power line pops and reduces the receiver's gain (blanks it) for the brief duration of each pulse. Because the pulses are very short, muting during them removes the noise with little loss of the wanted signal.

• A. Widening the received bandwidth would admit more noise rather than remove pulses; a blanker mutes the receiver during each pulse.
• B. Noise pulses are not redirected into a capacitor; the blanker briefly reduces gain while each pulse lasts.
• D. Clipping noise peaks describes a noise limiter, which cuts off peaks above a set level; a blanker instead reduces the receiver gain during each pulse.

B. A pronounced dip

In a vacuum-tube amplifier, the TUNE (plate) control brings the output tank circuit to resonance at the operating frequency. At resonance the tank presents its highest impedance to the tube, so plate current falls to a pronounced dip, and the operator tunes for that dip.

• A. Plate current rises as the tank moves off resonance; at the correct setting it falls to a minimum, not a peak.
• C. Plate current changes sharply as the tank passes through resonance, which is why the dip is used to find the correct setting.
• D. Correct tuning produces a steady dip in plate current, not a slow, rhythmic change.

C. To prevent excessive drive

Automatic level control is a feedback voltage that reduces the transceiver's output when drive to the amplifier gets too high. Overdriving a linear amplifier pushes it into nonlinear operation, causing distortion and splatter, so ALC keeps drive within the range the amplifier handles cleanly.

• A. Transmit audio frequency response is shaped by equalization and filtering, not by ALC.
• B. Harmonics are reduced by low-pass filtering and the output tank circuit; ALC controls drive level.
• D. ALC does not increase efficiency; it reduces drive when it gets too high so the amplifier stays linear.

C. Increase power transfer from the transmitter to the feed line

An antenna tuner is an impedance matching network that transforms the impedance at the transmitter end of the feed line to the 50 ohms the transmitter is designed for. The transmitter can then deliver full power into the feed line, but the tuner does not change the mismatch, SWR or loss on the feed line between the tuner and the antenna.

• A. A tuner at the transmitter does not change the SWR on the feed line beyond it; that is set by the antenna and feed line impedances.
• B. Feed line loss depends on the line itself and the SWR on it, which a tuner at the transmitter end does not change.
• D. A tuner does not reduce feed line SWR or feed line loss, so not all the choices are correct.

A. Received signals may become distorted

Receiver noise reduction, usually done with digital signal processing, tries to separate the wanted signal from noise and suppresses whatever it judges to be noise. At higher settings it removes more of the signal along with the noise, so voices can sound hollow, watery or distorted.

• B. Noise reduction processes the received signal and does not affect the stability of the receiver's frequency.
• C. Noise reduction tends to preserve steady tones such as CW; its typical side effect at high settings is distortion, not severe loss of CW signals.
• D. Noise reduction does not change the tuned frequency; the receiver stays where it is set.

D. Desired power output without exceeding maximum allowable plate current

The LOAD (or COUPLING) control matches the tube to the antenna system and sets how much power is drawn from the tube. Increasing loading raises both output and plate current, so the operator adjusts it, re-dipping with the TUNE control, until the desired output is reached without exceeding the tube's maximum allowable plate current.

• A. The SWR on the antenna and feed line is set by the antenna system, not by the amplifier's LOAD control.
• B. Minimizing plate current would mean little power output; the LOAD control is set for the desired output within the plate current rating.
• C. Plate voltage is set by the amplifier's power supply, not by the LOAD control.

C. To allow time for the amplifier to switch the antenna between the transceiver and the amplifier output

When a transceiver keys an external amplifier, relays in the amplifier take a short time, typically milliseconds, to switch the antenna from the bypass path to the amplifier output. Delaying RF output until the relays settle prevents hot switching, which can damage relay contacts and cause a brief, high SWR.

• A. Key clicks come from CW keying edges that are too abrupt and are controlled by shaping the keying waveform, not by a keying-line delay.
• B. Overmodulation is a matter of audio levels and drive, not of the amplifier's antenna switching time.
• D. The amplifier's power supply is already running when it is switched on; the delay covers relay switching, not power supply startup.

B. Automatic generation of dots and dashes for CW operation

An electronic keyer turns paddle movements into correctly timed CW: holding one paddle sends a string of dots and the other a string of dashes, at a set speed with correct spacing. Many transceivers include a built-in keyer.

• A. Transmit and receive switching is done by the transceiver's T/R circuits, VOX or break-in, not by the keyer.
• C. Allowing time to switch an antenna is the job of a transmit delay setting, not a keyer.
• D. PSK and RTTY need a computer interface such as a sound card interface, not a CW keyer.

B. The ALC action distorts the signal

AFSK data modes send audio tones whose amplitude and phase must be reproduced cleanly. ALC action changes the transmitter gain in response to the signal, which distorts it and can widen it, so operators set the audio drive low enough that ALC stays inactive.

• A. ALC adjusts gain; it does not invert the modulation of an AFSK signal.
• C. Overheating comes from long, high-duty-cycle transmissions at too much power, not from ALC activity.
• D. ALC does not invert modulation or cause overheating, so not all the choices are correct.

C. To transmit on one frequency and listen on another

With two VFOs, a transceiver can receive on one frequency and transmit on another, called split operation. DX stations often listen a few kHz away from their transmit frequency to spread out callers, and the second VFO makes this easy.

• A. A dual-VFO transceiver transmits on only one frequency at a time; the second VFO sets a second frequency to switch to.
• B. Dual VFOs let a transceiver switch between two frequencies; they do not make it transmit and receive at the same time.
• D. VFO stands for variable frequency oscillator, and the second one adds a second tuned frequency; it does not improve frequency accuracy.

A. To prevent receiver overload from strong incoming signals

A receive attenuator reduces the level of all signals at the receiver input by a set number of decibels. With a very strong nearby signal, that keeps the receiver's front end from overloading and producing intermodulation or desensitization, at the cost of weakening weak signals too.

• B. Transmitter drive to a linear amplifier is set with the transmitter's power control; a receive attenuator acts only on received signals.
• C. A receive attenuator is a passive network in the signal path and does not meaningfully reduce power consumption.
• D. Audio level is set with the volume control; the attenuator reduces RF signal strength at the receiver input to prevent overload.

D. An oscilloscope

An oscilloscope draws a graph of a signal on its screen. The vertical channel amplifier scales the signal voltage to move the trace up and down, and the horizontal channel amplifier moves it across the screen, usually driven by a time base, so the instrument displays waveforms.

• A. An ohmmeter measures resistance as a single reading; it has no horizontal or vertical display channels.
• B. A signal generator produces test signals rather than displaying them.
• C. An ammeter measures current as a single value and has no display channels.

D. Complex waveforms can be measured

A digital voltmeter reports a single number, such as an RMS or average value, while an oscilloscope shows the shape of a voltage over time. That lets you see distortion, pulses, modulation envelopes and other complex waveforms that a meter reduces to one reading.

• A. An oscilloscope usually uses more power than a voltmeter, so lower power use is not an advantage.
• B. Complex impedances are measured with impedance bridges, antenna analyzers or network analyzers, not easily with an oscilloscope.
• C. A good digital voltmeter usually reads voltage more precisely than an oscilloscope; the scope's advantage is showing the waveform.

A. An oscilloscope

An oscilloscope displays the envelope of the transmitted CW signal, so you can see the rise and fall of each keyed element. Edges that are too abrupt cause key clicks, while edges that are too slow make the code sound soft, so the scope shows whether keying is shaped properly.

• B. A field strength meter shows relative signal strength, not the shape of individual keyed elements.
• C. A sidetone monitor produces an audio tone inside the radio when you key; it does not show the transmitted RF waveform.
• D. A wavemeter indicates approximate frequency, not the shape of the keying waveform.

D. The attenuated RF output of the transmitter

To see the RF envelope, a sample of the transmitter's actual RF output, reduced by an attenuator or sampler to a safe level, goes to the oscilloscope's vertical input. The trace then shows the envelope of the transmitted signal, such as the shape of CW keying or a two-tone test pattern.

• A. The local oscillator is an internal signal used for frequency conversion, not the transmitted output whose envelope you want to see.
• B. An external RF oscillator would show its own signal, not the envelope of the transmitted signal.
• C. The balanced mixer output is an internal low-level stage before amplification and filtering, not the final transmitted signal.

D. It decreases the loading on circuits being measured

A voltmeter connects in parallel with the part of the circuit it measures, so any current it draws changes the voltage being measured. A high input impedance, often around 10 megohms for a digital meter, draws very little current, keeping the reading close to the true circuit voltage.

• A. High input impedance does not set the meter's frequency response; its purpose is to keep the meter from loading the circuit.
• B. Safe measurement of high voltages depends on the meter's voltage rating and insulation, not on its input impedance.
• C. Resolution depends on the display and converter, such as how many digits a digital meter shows, not on input impedance.

C. Higher precision

A digital multimeter displays its reading as digits, so you can read a value to several significant figures without interpreting a needle's position on a scale. That gives it higher precision than a typical analog multimeter.

• A. Either type of meter can measure voltages in computer circuits; the digital meter's main advantage is the precision of its numeric display.
• B. Digital meters are not inherently less prone to overload; either type can be damaged by excessive voltage or current on the wrong range.
• D. An analog meter's needle shows changing values more readily, which is why it is preferred for peaking and dipping adjustments.

B. Two non-harmonically related audio signals

A two-tone test feeds two audio tones of equal level into an SSB transmitter's audio input, for example 700 Hz and 1900 Hz, chosen so neither is a harmonic of the other. The output then shows whether the transmitter reproduces both tones without creating extra intermodulation products.

• A. Two tones of the same frequency shifted 90 degrees add up to a single tone, which cannot reveal intermodulation.
• C. Swept tones are used to measure frequency response, not to run a two-tone linearity test.
• D. Square waves contain many harmonics, which would confuse the measurement; the test uses two sine-wave tones.

A. Linearity

A linear amplifier's output should be an exact scaled copy of its input. When two tones go in, any nonlinearity creates intermodulation products at new frequencies and distorts the envelope pattern on an oscilloscope, so the two-tone test measures the transmitter's linearity.

• B. Carrier and unwanted sideband suppression are separate SSB measurements; the two-tone test looks for distortion caused by nonlinearity.
• C. Percentage of frequency modulation applies to FM transmitters; the two-tone test examines the amplitude linearity of an SSB transmitter.
• D. Carrier phase shift is not what the two-tone test analyzes; it reveals nonlinearity through intermodulation products.

D. When adjusting circuits for maximum or minimum values

An analog meter's needle moves smoothly and continuously, so you can watch a value rise to a peak or fall to a dip as you turn an adjustment. A digital display updates a few times per second with changing digits, which makes trends harder to follow while tuning.

• A. Logic circuits switch between fixed voltage levels that a digital meter or logic probe reads well; an analog meter offers no advantage there.
• B. High precision is an advantage of a digital multimeter, not an analog one.
• C. An ordinary analog multimeter cannot measure an oscillator's frequency; that takes a frequency counter.

A. Standing wave ratio

A directional wattmeter measures forward power and reflected power separately, and SWR follows from the two readings: SWR = (1 + √(Pr / Pf)) / (1 - √(Pr / Pf)). For example, 100 W forward and 4 W reflected gives √0.04 = 0.2, so SWR = 1.2 / 0.8 = 1.5:1.

• B. Front-to-back ratio compares an antenna's radiation in two directions and requires measuring field strength around the antenna.
• C. RF interference is identified by listening and by locating its source, not by forward and reflected power readings.
• D. Propagation depends on the ionosphere and the path, which a wattmeter in the feed line cannot measure.

C. Antenna and feed line

An antenna analyzer contains its own low-power signal source and measuring circuit. To measure SWR you connect it to the antenna system's feed line in place of the transceiver; no transmitter or receiver is needed.

• A. The analyzer has its own detector, so a receiver is not needed.
• B. The analyzer generates its own low-level test signal, so a transmitter is not needed and could damage the analyzer.
• D. Neither a receiver nor a transmitter is needed, so not all the choices are correct.

B. Received power that interferes with SWR readings

An antenna analyzer measures SWR using its own very low-power signal. A strong signal from a nearby transmitter, picked up by the antenna, adds unwanted power at the analyzer's detector, so the SWR and impedance readings become inaccurate.

• A. Desensitization and intermodulation are not the mechanism; the received power itself reaches the analyzer's detector and upsets the reading.
• C. Nearby signals do not make the analyzer generate harmonics; they add received power that throws off the SWR reading.
• D. Only the received power effect applies, so not all the choices are correct.

C. Impedance of coaxial cable

An antenna analyzer measures the impedance of whatever is connected to it at the frequency it generates. Connected to a length of coaxial cable, it can measure the cable's impedance, which also lets you find the cable's characteristic impedance and electrical length.

• A. Front-to-back ratio requires measuring the radiated field in front of and behind the antenna, which an analyzer at the feed line cannot do.
• B. An antenna analyzer generates only a low-level test signal and must not be connected to a transmitter's output; power is measured with a wattmeter.
• D. Antenna gain describes radiation in a direction compared with a reference antenna; an analyzer measures impedance, not radiation.

B. Bypass capacitor

A capacitor's reactance falls as frequency rises (Xc = 1 / (2πfC)). A 0.01 µF bypass capacitor from an audio line to ground has about 1.1 ohms of reactance at 14 MHz but about 15.9 kilohms at 1 kHz, so it shunts RF to ground while leaving the audio signal nearly untouched.

• A. An inductor's reactance rises with frequency, so connected to ground it would short out the audio while blocking RF, the opposite of what is needed.
• C. A diode does not bypass RF to ground; diode junctions that rectify RF are a common cause of audio interference.
• D. A reverse-biased diode acts mainly as a small capacitance and is not a practical RF bypass; diode junctions that rectify RF are a common cause of audio interference.

C. Arcing at a poor electrical connection

An electric arc, such as at a loose or corroded connection on a power line, produces sharp bursts of current that contain energy across a very wide range of frequencies. The result is a buzzing or crackling noise heard across many bands.

• A. Feeding a balanced antenna without a balun can put common-mode current on the feed line and cause local RF problems, but it does not produce noise across a wide range of frequencies.
• B. Rectification of a transmitter's signal, for example at a corroded junction, can cause interference; a lack of rectification is not a cause.
• D. A balun used with an unbalanced antenna may be unnecessary, but it does not generate interference across a wide range of frequencies.

C. Distorted speech

An audio device that picks up an SSB signal rectifies it, recovering the varying envelope without the carrier needed to demodulate SSB properly. The result is distorted, garbled speech that rises and falls with the operator's voice.

• A. An SSB transmitter puts out RF only when the operator speaks, so it does not cause a steady hum the whole time it is on the air.
• B. On-and-off humming or clicking matches a keyed CW transmitter, not SSB voice.
• D. Without the carrier needed to demodulate SSB, the audio device cannot reproduce clear speech; the speech it produces is distorted.

A. On-and-off humming or clicking

A CW transmitter turns its carrier on and off. An audio device that rectifies the RF responds to each keyed element, producing humming, thumps or clicks that follow the keying.

• B. Rectifying a CW carrier produces a change in level, not a clean audio tone; hearing CW as a tone requires a receiver's beat frequency oscillator.
• C. A chirpy CW signal is what a receiver hears from a transmitter whose frequency shifts during keying; an audio device rectifying RF does not reproduce chirp.
• D. Severely distorted audio describes interference from a voice signal such as SSB, not from keyed CW.

D. The ground wire has high impedance on that frequency

A ground wire whose length is a significant fraction of a wavelength, such as about a quarter wavelength, presents a high impedance at the equipment end at that frequency. RF current then cannot flow to ground easily, so high RF voltage appears on equipment cases and microphones and can cause RF burns.

• A. Flat strap or braid has less inductance than round wire of similar size and is often preferred for RF grounding; it does not cause high voltages.
• B. Insulation on a ground wire does not cause high RF voltages; the wire's impedance at the operating frequency, set largely by its length, does.
• C. The cause is the high impedance of the ground wire at the operating frequency, not resonance of the ground rod itself.

C. High RF voltages on the enclosures of station equipment

A ground wire about a quarter wavelength long (about 5.4 m at 14 MHz) behaves like a shorted quarter-wave transmission line: shorted at the ground end, it presents a high impedance at the station end. The equipment chassis then carries high RF voltage instead of sitting near ground potential, which can cause RF burns and interference.

• A. A resonant ground connection presents a high impedance, so ground straps carry little current; the problem is high voltage, not overheating.
• B. Corrosion of a ground rod comes from moisture and dissimilar metals, not from the RF resonance of the ground connection.
• D. A ground loop forms when equipment is grounded through more than one path, which is a wiring layout issue, not a resonance effect.

A. A soldered joint will likely be destroyed by the heat of a lightning strike

A lightning strike drives an enormous current through ground connections, heating them enough to melt solder and leave the joint open when protection is needed. Lightning ground connections are therefore welded or made with mechanical clamps rated for the purpose.

• B. Solder flux has nothing to do with lightning ground performance; the problem is that the solder melts under the strike's heat.
• C. Dielectric constant describes insulators; solder is a conductor, so the term does not apply.
• D. Only the heat problem is real, so not all the choices are correct.

A. Place a ferrite choke on the cable

Common-mode current flows in the same direction on all conductors of a cable, often on the outside of the shield, so the cable acts as an antenna for RF. A ferrite choke around the cable adds impedance to that common-mode current while leaving the audio signal, which flows in opposite directions on the conductors, unaffected.

• B. Connecting the center conductor to the shield would short out the audio signal and make the cable useless.
• C. Grounding the center conductor shorts out the audio signal the cable is supposed to carry.
• D. An extra insulating jacket does not affect RF current flowing on the cable's conductors.

D. Bond equipment enclosures together

A ground loop forms when equipment is connected to ground through more than one path, so small voltage differences between the paths drive current around the loop and add hum or noise. Bonding all equipment enclosures together with short, heavy connections keeps them at the same potential and minimizes those currents.

• A. Connecting grounds in series daisy-chains the equipment, leaving voltage differences between units; it does not minimize ground loops.
• B. The AC neutral is bonded to ground only at the service entrance under electrical codes; connecting it elsewhere is unsafe and does not cure ground loops.
• C. Lock washers and star washers help make secure, low-resistance ground connections, so avoiding them would not help.

A. You receive reports of “hum” on your station’s transmitted signal

A ground loop in audio wiring, for example between a computer sound card interface and the radio, lets power line current flow in a cable shield. That adds hum at the power line frequency and its harmonics to the transmit audio, so other stations report hum on your signal.

• B. A sudden high SWR points to a problem in an antenna or feed line, not to the audio ground system.
• C. Excessive current draw points to a fault inside the equipment, such as a failed component, not to an audio ground loop.
• D. Harmonic interference comes from the transmitter's RF output and is cured by filtering, not by changing audio grounding.

C. Bonding all equipment enclosures together

RF hot spots are places where equipment cases or cables carry RF voltage relative to one another. Bonding all equipment enclosures together with short, wide conductors keeps them at the same RF potential, reducing hot spots and stray RF in the station.

• A. Metal enclosures shield the circuits inside, but separate enclosures can still sit at different RF potentials unless they are bonded together.
• B. Surge suppressor outlets protect against voltage spikes on the AC line; they do not equalize RF potential between equipment.
• D. Low-pass filters reduce harmonics leaving the transmitter; they do not prevent RF voltage differences between enclosures.

D. It ensures that hazardous voltages cannot appear on the chassis

If a live wire inside an AC-powered device touches its metal case, a grounded case gives the fault current a low-resistance path that trips the breaker or blows the fuse. Without that ground the case could sit at line voltage and shock anyone who touches it.

• A. Grounding does the opposite: with an internal short to the case, it makes the fuse or breaker open promptly, removing power.
• B. Signal overload is a receiver problem that grounding the enclosure does not prevent.
• C. The neutral is grounded at the building's electrical service entrance, not by grounding equipment enclosures.

A. Increase the apparent loudness of transmitted voice signals

A speech processor compresses or clips voice peaks so the quieter parts of speech are raised closer to the peak level. Average power rises while peak power stays the same, so the signal sounds louder and cuts through noise and interference more effectively.

• B. Speech processing is not used to add bass; communications audio usually reduces low frequencies to improve intelligibility.
• C. A speech processor adds some distortion, especially when overdriven; it does not prevent distortion.
• D. A speech processor does not cut high frequencies to keep a signal in band; staying in band depends on transmit filtering and on operating far enough from band edges.

B. It increases average power

Speech has high peaks with a much lower average power. A speech processor raises the lower-level parts of the waveform relative to the peaks, so average power goes up while peak envelope power stays at the transmitter's limit.

• A. Peak power is limited by the transmitter and amplifier; processing raises average power, not peak power.
• C. Processing, especially clipping, tends to add harmonic distortion rather than reduce it.
• D. Processing does not reduce intermodulation distortion; excessive processing adds distortion products to the signal.

D. All these choices are correct

Too much speech processing distorts the voice, generates intermodulation products that widen the signal and cause splatter, and raises the level of background noise picked up by the microphone along with the speech.

• A. Distorted speech is one result of a misadjusted processor, but intermodulation products and excessive background noise occur too.
• B. Excess intermodulation products are one result, but distorted speech and excessive background noise occur too.
• C. Excessive background noise is one result, because processing boosts quiet sounds such as room noise, but distortion and intermodulation occur too.

C. Received signal strength

An S meter on a receiver indicates the relative strength of the received signal, in S units from S1 to S9 and in decibels over S9 for stronger signals.

• A. Carrier suppression is checked with transmitter test equipment such as a spectrum analyzer, not an S meter.
• B. Impedance is measured with an antenna analyzer or impedance bridge, not an S meter.
• D. Transmitter power output is measured with a wattmeter; the S meter indicates received signal strength.

D. It is 100 times more powerful

Decibels express power ratios: ratio = 10^(dB / 10). A signal 20 dB over S9 is 10^(20 / 10) = 10^2 = 100 times more powerful than an S9 signal.

• A. A reading above S9 means more power, not less, and 20 dB is a factor of 100, not 10.
• B. A reading above S9 means more power, not less, and 20 dB is a factor of 100, not 20.
• C. 20 dB is not 20 times; each 10 dB is a factor of 10, so 20 dB is 10 x 10 = 100 times.

A. 6 dB

By the usual convention, one S unit represents 6 dB, which is about four times the power (10^(6 / 10) = 3.98) or twice the voltage. Real S meters often depart from this calibration, but 6 dB per S unit is the standard figure.

• B. 12 dB would be two S units under the 6 dB convention.
• C. 15 dB is not the standard S unit; it would be two and a half S units.
• D. 18 dB corresponds to three S units, not one.

C. Approximately 4 times

One S unit is 6 dB, and a 6 dB increase is a power ratio of 10^(6 / 10) = 3.98. Raising the reading at the distant receiver from S8 to S9 therefore takes about 4 times the transmitter power, such as going from 25 W to 100 W.

• A. 1.5 times the power is only about 1.8 dB, well short of one S unit.
• B. 2 times the power is about 3 dB, half of an S unit.
• D. 8 times the power is about 9 dB, one and a half S units.

C. 7.175 MHz to 7.178 MHz

Lower sideband places the signal below the displayed carrier frequency. A 3 kHz wide LSB signal with the carrier at 7.178 MHz occupies 7.178 - 0.003 = 7.175 MHz up to 7.178 MHz, which puts its lower edge exactly at 7.175 MHz, the bottom of the General class phone segment on 40 meters.

• A. 7.178 to 7.181 MHz is where an upper sideband signal would be; LSB extends below the carrier.
• B. 7.178 to 7.184 MHz is 6 kHz wide and above the carrier, which fits neither a 3 kHz signal nor LSB.
• D. 7.1765 to 7.1795 MHz centers the signal on the carrier, but a sideband signal lies entirely on one side of its carrier.

B. 14.347 MHz to 14.350 MHz

Upper sideband places the signal above the displayed carrier frequency. A 3 kHz wide USB signal with the carrier at 14.347 MHz occupies 14.347 MHz up to 14.347 + 0.003 = 14.350 MHz, which ends exactly at 14.350 MHz, the top of the 20 meter band.

• A. 14.347 to 14.647 MHz is 300 kHz wide; it mistakes 3 kHz for 0.3 MHz.
• C. 14.344 to 14.347 MHz lies below the carrier, where a lower sideband signal would be.
• D. 14.3455 to 14.3485 MHz centers the signal on the carrier, but a sideband signal lies entirely on one side of its carrier.

A. At least 3 kHz above the edge of the segment

An LSB signal extends below its displayed carrier frequency, and 47 CFR 97.307(b) requires emissions resulting from modulation to be confined to the band or segment available to the control operator. A 3 kHz wide LSB signal therefore needs its carrier at least 3 kHz above the lower edge, for example 7.178 MHz or higher where a General's 40 meter phone segment starts at 7.175 MHz.

• B. A carrier below the lower edge puts the entire LSB signal outside the segment.
• C. A carrier below the lower edge puts the entire LSB signal outside the segment.
• D. A carrier only 1 kHz above the edge leaves 2 kHz of a 3 kHz wide LSB signal below the segment edge.

B. At least 3 kHz below the edge of the band

A USB signal extends above its displayed carrier frequency, and 47 CFR 97.307(b) requires emissions resulting from modulation to be confined to the band or segment available to the control operator. A 3 kHz wide USB signal therefore needs its carrier at least 3 kHz below the upper edge, for example 14.347 MHz or lower at the 14.350 MHz top of the 20 meter band.

• A. A carrier above the upper edge puts the entire USB signal outside the band.
• C. A carrier above the upper edge puts the entire USB signal outside the segment.
• D. A carrier only 1 kHz below the edge leaves 2 kHz of a 3 kHz wide USB signal beyond the segment edge.

C. To electrically lengthen a physically short antenna

A capacitance hat is a set of spokes, a disk or a similar structure near the top of a shortened vertical antenna. It adds capacitance at the top, which keeps current flowing higher up the antenna and lowers its resonant frequency, so a physically short antenna acts electrically longer and needs less loading inductance.

• A. A capacitance hat does not raise power handling; its purpose is to make the antenna act electrically longer.
• B. Top loading with a capacitance hat raises radiation resistance by keeping more current higher up the antenna, the opposite of reducing it.
• D. Lowering the radiation angle is not the purpose of a capacitance hat; it makes a short antenna resonate at a lower frequency.

D. To reduce RF voltage discharge from the tip of the antenna while transmitting

The tip of a shortened HF mobile antenna carries very high RF voltage while transmitting. A sharp point concentrates the electric field and can produce corona discharge, so a smooth ball on the tip spreads the field over a larger surface and reduces the discharge.

• A. Narrowing the operating bandwidth is not the purpose; the ball smooths the tip to reduce discharge.
• B. Raising the antenna's Q is not the purpose; the ball limits corona discharge at the high-voltage tip.
• C. Protection from impacts is not the purpose; the ball spreads the high RF voltage at the tip to reduce discharge.

A. To the battery using heavy-gauge wire

A 100 W HF transceiver can draw around 20 A when transmitting. Connecting it directly to the battery with heavy-gauge wire, fused close to the battery, keeps voltage drop low, and the battery helps smooth out electrical noise and voltage spikes from the vehicle's charging system.

• B. The alternator's output carries voltage spikes and noise, and it is not a suitable direct connection point for a transceiver; the battery is.
• C. Balanced transmission line is designed to carry RF, not high DC current; power wiring should be heavy-gauge wire.
• D. This combines two errors: the alternator is the wrong connection point and balanced transmission line is not power wire.

B. The socket’s wiring may be inadequate for the current drawn by the transceiver

A 100 W HF transceiver can draw around 20 A when transmitting. The wiring and fuse for a vehicle's auxiliary power socket are often not rated for that much current, which can cause excessive voltage drop, blown fuses or overheated wiring.

• A. DC power wiring does not need RF shielding; the problem is that the socket's wiring may not carry the current.
• C. The socket's DC polarity is not reversed relative to transceivers; the concern is that its wiring cannot safely carry the transceiver's current.
• D. Drawing power from the socket does not overheat the engine; the risk is to the socket's wiring and fuse.

C. Efficiency of the electrically short antenna

HF wavelengths are long (about 79 m at 3.8 MHz), so a vehicle antenna is a small fraction of a wavelength. Its low radiation resistance compared with losses in the loading coil and ground system turns much of the transmitter power into heat, which limits a mobile station more than its other constraints.

• A. Picket fencing is the rapid flutter heard as a mobile station moves past obstructions, mainly on VHF FM; it is a nuisance, not the main HF mobile limitation.
• B. Proper heavy-gauge wire solves DC power wiring problems; the antenna's efficiency remains the main limit.
• D. Part 97 has no separate power limit for mobile stations on 75 meters; the 1.5 kW PEP limit in 47 CFR 97.313(b) applies to all stations.

C. Operating bandwidth may be very limited

A shortened antenna relies on a loading coil to reach resonance, which gives it a high Q. A high-Q antenna stays well matched over only a narrow range of frequencies, so on the lower HF bands a small change in operating frequency can require retuning.

• A. A short antenna does not distort the transmitted modulation; its drawbacks are low efficiency and narrow bandwidth.
• B. Loaded short antennas have a high Q, not a low one, and that high Q is what narrows their bandwidth.
• D. Harmonic radiation is controlled by the transmitter's filtering; a short antenna does not increase it.

D. All these choices are correct

Modern vehicles contain many sources of electrical noise. The alternator and charging system create whine, electric fuel pumps generate motor noise, and the engine and body control computers radiate digital noise, all of which can be heard in an HF receiver.

• A. The battery charging system, especially alternator whine, can cause interference, but it is not the only source.
• B. The fuel delivery system, including the electric fuel pump, can cause interference, but other systems do too.
• C. Control computers radiate noise from their digital circuits, but they are one of several sources.

A. Series-parallel

Solar cells are connected in series to add their voltages (each silicon cell gives about 0.5 V), and series strings are connected in parallel to add their currents. This series-parallel arrangement lets a panel reach a useful voltage and current; 36 cells in series is a common design for charging 12 V batteries.

• B. Shunt describes a component placed in parallel, such as a meter shunt; it is not the arrangement of cells in a panel.
• C. Bypass diodes are added across groups of cells to carry current around shaded cells, but bypass is not how the cells themselves are connected.
• D. A full-wave bridge is a four-diode rectifier that converts AC to DC; solar cells already produce DC.

B. 0.5 VDC

A fully illuminated silicon photovoltaic cell produces roughly 0.5 to 0.6 V open circuit, set by the properties of the silicon junction regardless of the cell's size. Cell area sets the current, so panels connect many cells in series to reach useful voltages.

• A. 0.02 V is far too low; a silicon cell in full sun produces about 0.5 V.
• C. 0.2 V is too low for an illuminated silicon cell, which produces about 0.5 V.
• D. 1.38 V is far more than one silicon solar cell produces; it would take nearly three cells in series.

B. To prevent discharge of the battery through the panel during times of low or no illumination

When the panel is dark, its voltage falls below the battery's, and current would flow backward from the battery through the panel. A series (blocking) diode conducts only from the panel to the battery, so it stops this discharge.

• A. A diode does not regulate voltage; that is the job of a charge controller.
• C. A series diode does not limit current to a set value; it conducts in one direction only.
• D. Protecting the battery from excessive voltage takes a charge controller; a diode only blocks reverse current.

D. The solar panel must have a charge controller

Lithium iron phosphate batteries must be charged within specific voltage and current limits, and overcharging can damage them and create a safety hazard. A charge controller set for LiFePO4 regulates the panel's output to the correct charging profile.

• A. Grounding the panel frame is sound electrical practice, but it does not protect the battery from incorrect charging.
• B. Mounting orientation does not address the main risk, which is charging the battery at the wrong voltage or current.
• C. A series resistor wastes power and cannot regulate the charging voltage; a charge controller is needed.