G8 Signals and Emissions

B. By changing an oscillator’s frequency directly with a digital control signal

In direct FSK, the data signal itself shifts the transmitter oscillator between two frequencies (mark and space), so the RF carrier moves as each bit changes. This differs from AFSK, where audio tones are fed into an SSB transmitter.

• A. Keying an FM transmitter with a sub-audible tone is CTCSS (tone squelch) for repeater access, not a way to send binary data.
• C. A computer interface protocol (CAT control) changes the radio's settings, such as the dial frequency; it does not shift the carrier for each data bit.
• D. The CW keying input switches the carrier on and off; it does not move an oscillator between two frequencies.

B. Phase modulation

Phase modulation conveys information by shifting the phase angle of the RF signal in step with the modulating signal. Digital modes such as PSK31 use the same idea with discrete phase shifts.

• A. Convolution is a mathematical operation used in signal processing and coding; "phase convolution" is not a modulation method.
• C. "Phase transformation" is not the name of any modulation process.
• D. Phase inversion is a single 180-degree flip of a signal; it is not the general name for conveying information by varying phase.

D. Frequency modulation

Frequency modulation conveys information by varying the instantaneous frequency of the carrier above and below its resting value in step with the modulating signal, while the amplitude stays constant.

• A. "Frequency convolution" is not a modulation method; convolution is a mathematical operation.
• B. "Frequency transformation" is not the name of any modulation process.
• C. Frequency conversion shifts a whole signal to a different frequency by mixing, as in a superheterodyne receiver; it moves the signal but does not add information to it.

B. Phase modulation

A reactance modulator varies a capacitance or inductance in step with the audio. Connected to an RF amplifier stage, it shifts the phase of the signal passing through, producing phase modulation; connected to the oscillator itself, it would vary the frequency directly and produce FM.

• A. Multiplex modulation combines several information channels on one carrier; a reactance modulator does not do this.
• C. Amplitude modulation varies the carrier's strength; a reactance modulator varies a reactance, which shifts phase rather than amplitude.
• D. Pulse modulation varies the timing, width, or height of a train of pulses, which a reactance modulator does not produce.

D. Amplitude modulation

Amplitude modulation varies the strength of the RF signal with the modulating signal, so the signal's instantaneous power rises and falls. FM and PM signals keep a constant amplitude and power.

• A. "Power modulation" is not a standard name for a modulation type; varying the RF power level is amplitude modulation.
• B. Phase modulation varies the phase of the carrier while its amplitude, and so its power, stays constant.
• C. Frequency modulation varies the frequency of the carrier while its amplitude, and so its power, stays constant.

D. All these choices are correct

QPSK31 is the four-phase version of PSK31. It keeps the 31.25-baud symbol rate of BPSK31, so its bandwidth is about the same, uses the extra phase states to carry error-correcting code, and depends on both stations using the same sideband.

• A. True: receiving QPSK31 on the opposite sideband reverses the direction of its 90-degree phase shifts, so both stations must use the same sideband, but this is only one of the characteristics.
• B. True: QPSK31 adds a convolutional code that the receiver decodes to correct errors, but this is only one of the characteristics.
• C. True: QPSK31 uses the same 31.25-baud symbol rate as BPSK31, so its bandwidth is about the same, but this is only one of the characteristics.

A. Single sideband

Single sideband removes the carrier and one of the two sidebands of an AM signal, so a voice SSB signal occupies only about 3 kHz. Every other phone emission listed takes more spectrum.

• B. Vestigial sideband sends one full sideband plus part of the other (it is used for analog television), so it is wider than SSB.
• C. Phase modulation produces sideband pairs on both sides of the carrier, like FM, and occupies several times the bandwidth of SSB.
• D. FM phone with 5 kHz deviation and 3 kHz audio occupies about 2 x (5 + 3) = 16 kHz by Carson's rule, several times the width of SSB.

D. Excessive bandwidth

Overmodulation drives the signal past its linear limits, which distorts the waveform and adds frequency components that are not in the original audio. These spread the signal far beyond its normal width (splatter) and interfere with nearby stations.

• A. Overmodulation comes from too much audio, not too little.
• B. Overmodulation widens the signal; it does not make the bandwidth too narrow.
• C. Frequency drift is a slow change of the carrier frequency caused by oscillator instability, such as temperature changes, not by modulation level.

A. 8-tone frequency shift keying

FT8 sends its data by shifting among eight audio tones spaced 6.25 Hz apart, which is 8-tone frequency shift keying (8-FSK). The whole signal fits in about 8 x 6.25 = 50 Hz.

• B. Vestigial sideband is used for analog television, not FT8.
• C. FT8 is not an AM mode; it keeps a constant amplitude and changes only its tone frequency.
• D. FT8 is a narrow 50 Hz signal, not spread spectrum; direct sequence spread spectrum spreads a signal over a much wider band.

C. Signal distortion caused by excessive drive or speech levels

Flat-topping happens when excessive drive or speech level pushes an amplifier past its maximum output. The peaks of the modulation envelope are clipped flat, which distorts the signal and causes splatter.

• A. Flat-topping comes from driving the amplifier beyond its linear range with too much drive or audio, not from too little collector current.
• B. Properly adjusted ALC limits drive and helps prevent flat-topping; it does not describe the distortion itself.
• D. Carrier suppression is a function of the balanced modulator in an SSB transmitter and has nothing to do with clipped peaks.

A. The waveform created by connecting the peak values of the modulated signal

The modulation envelope is the outline traced by connecting the peaks of the RF waveform. In AM it follows the shape of the modulating audio, which is what an oscilloscope shows when you view an AM signal.

• B. The carrier frequency is the RF frequency being modulated; the envelope is the shape of its peak amplitude over time.
• C. Unwanted signals that spill onto nearby frequencies are splatter or spurious emissions, not the envelope.
• D. Bandwidth is how much spectrum the signal occupies, a frequency-domain measure; the envelope is a waveform seen over time.

D. Modulation in which digital data is transmitted using 0-, 90-, 180- and 270-degrees phase shift to represent pairs of bits

QPSK (quadrature phase shift keying) uses four phase states, 0, 90, 180 and 270 degrees, so each symbol carries two bits. Sending two bits per symbol doubles the data rate of two-phase BPSK at the same symbol rate.

• A. "Quasi-parallel to serial conversion" is not what the Q in QPSK means; Q stands for quadrature, the 90-degree phase steps.
• B. "Quadra-pole sideband keying" is not a real technique, and QPSK is not a spread spectrum method.
• C. QPSK does not generate harmonics of the carrier; it changes the phase of a single carrier, and harmonics would be unwanted spurious emissions.

C. The sum of transmit power and antenna gains minus system losses as seen at the receiver

A link budget adds up everything between the transmitter and the receiver: transmitter power plus antenna gains, minus feed line, path and other losses, giving the signal power expected at the receiver. It is usually worked in decibels (dBm and dB) so the terms add and subtract.

• A. A link budget is an engineering calculation of signal power, not the money spent operating a link.
• B. Antenna gains minus losses leaves out the transmitter power, so it cannot give the signal level arriving at the receiver.
• D. Transmit power minus receiver sensitivity ignores antenna gains and losses, so it does not give the signal level expected at the receiver.

B. The difference between received power level and minimum required signal level at the input to the receiver

Link margin is how much stronger the received signal is than the minimum level the receiver needs. For example, a signal arriving at -95 dBm at a receiver that needs -110 dBm has (-95 dBm) - (-110 dBm) = 15 dB of margin to absorb fading and other losses.

• A. Fade margin is essentially the same idea, the extra signal available to ride through fading, not its opposite.
• C. Transmit power minus receiver sensitivity ignores antenna gains and path loss, so it does not show how much extra signal actually reaches the receiver.
• D. Sensitivity plus 3 dB is only a signal level; margin depends on how strong the received signal actually is.

B. Local oscillator

A mixer outputs the sum and difference of its two inputs, so changing the local oscillator frequency selects which incoming signal lands on the fixed intermediate frequency. Tuning a superheterodyne receiver means tuning its LO.

• A. The image frequency is an unwanted input that the mixer also converts to the IF; the receiver tries to reject it, not tune it.
• C. The RF input is the received signal, whose frequency is set by the transmitting station; the receiver selects it by changing the LO.
• D. A beat frequency oscillator (BFO) feeds the product detector at the end of the IF chain to make CW and SSB audible; it does not convert signals to the IF.

B. Image response

A mixer converts two input frequencies to the same IF: one above the LO and one below it, separated by twice the IF. For example, with a 9 MHz IF and the LO at 23 MHz to receive 14 MHz, a signal at 23 + 9 = 32 MHz also produces 9 MHz; this unwanted reception is the image response.

• A. "Quadrature" refers to signals 90 degrees apart in phase, as in I/Q processing; it is not the name for interference at twice the IF.
• C. "Mixer interference" is a general description, not the specific term for a response at twice the IF from the desired signal.
• D. "Intermediate interference" is not a standard term; the response at twice the IF away is called the image.

A. Heterodyning

Heterodyning means mixing two RF signals in a nonlinear circuit to produce new signals at their sum and difference frequencies. It is the basis of the superheterodyne receiver and of frequency conversion in transmitters.

• B. Synthesizing means generating frequencies, as a frequency synthesizer does with a PLL or DDS, not mixing two signals.
• C. Frequency inversion means flipping a spectrum so high and low frequencies trade places; it is not the general term for mixing.
• D. Phase inversion is a 180-degree flip of a single signal, not the combining of two signals.

D. Multiplier

A frequency multiplier is a stage driven into nonlinear operation, so its output is rich in harmonics, with a tuned circuit that selects the wanted harmonic. For example, multiplying a 12.21 MHz oscillator by 12 gives 12.21 x 12 = 146.52 MHz.

• A. A mixer produces the sum and difference of two input frequencies; it does not generate a harmonic of one signal.
• B. A reactance modulator applies FM or PM to a signal; it does not raise its frequency.
• C. A balanced converter is a mixer arrangement that shifts frequency by combining two signals, not a stage that generates harmonics.

C. Odd-order

Odd-order products such as 2F1 - F2 and 2F2 - F1 (third order) fall right next to the original signals. For example, signals at 14.200 and 14.210 MHz produce third-order products at 14.190 and 14.220 MHz, inside the same band where filters cannot remove them.

• A. Second harmonics fall at twice each frequency, about 28.4 MHz in the example, far from the original signals.
• B. Even-order products such as F1 + F2 (28.410 MHz in the example) and F2 - F1 (0.010 MHz) fall far from the original signals.
• D. The intercept point is a measure of how linear a receiver or amplifier is, not an intermodulation product.

D. 16 kHz

Carson's rule estimates FM bandwidth as twice the sum of the peak deviation and the highest modulating frequency: BW = 2 x (5 kHz + 3 kHz) = 16 kHz.

• A. 3 kHz is only the modulating frequency, not the bandwidth of the FM signal.
• B. 5 kHz is only the peak deviation, not the bandwidth of the FM signal.
• C. 8 kHz is deviation plus modulating frequency, which covers only one side of the carrier; Carson's rule doubles it to 16 kHz.

B. 416.7 Hz

The multiplier chain raises the oscillator frequency by 146.52 MHz / 12.21 MHz = 12, and it multiplies the deviation by the same factor. To get 5 kHz of deviation at the output, the oscillator needs 5000 Hz / 12 ≈ 416.7 Hz.

• A. 101.75 Hz would require a multiplication factor of about 49 (5000 / 101.75 ≈ 49.1), but the factor here is 12.
• C. 5 kHz is the deviation at the transmitter output, after multiplication; the oscillator deviation is 12 times smaller.
• D. 60 kHz is 5 kHz multiplied by 12, the opposite of what is needed; the deviation must be divided by the multiplication factor.

B. Some modes have high duty cycles that could exceed the transmitter’s average power rating

Duty cycle is the fraction of time a mode transmits at full power. Modes such as FM, RTTY and FT8 run near 100 percent duty cycle, unlike SSB voice or CW, so a transmitter rated for full power on SSB may overheat unless its power is reduced for those modes.

• A. Duty cycle tells how hard a mode works the transmitter over time; it does not help in tuning it.
• C. Letting the other station break in depends on the operator's pauses and the radio's break-in setting, not on the mode's duty cycle.
• D. Overmodulation is controlled by audio and drive levels, not by knowing the duty cycle of the mode.

D. It results in the best signal-to-noise ratio

Noise power in a receiver rises in proportion to its bandwidth, so a filter only as wide as the signal passes the signal while rejecting noise outside it. For example, narrowing from 2400 Hz to 500 Hz for CW reduces noise by 10 log(2400 / 500) ≈ 6.8 dB.

• A. FCC rules limit transmitted bandwidth, not the bandwidth of receiver filters.
• B. Filter bandwidth has no meaningful effect on how much power a receiver draws.
• C. Impedance matching depends on the antenna and feed line, not on the receiver filter bandwidth.

B. Higher symbol rates require wider bandwidth

Each change of symbol creates sidebands, and the faster the symbols change, the farther those sidebands extend from the carrier, so higher symbol rates occupy wider bandwidth. Current rules regulate the result directly: since 2024-01-08, 47 CFR 97.307(f)(3) sets a 2.8 kHz authorized bandwidth for RTTY and data on 160 m through 10 m, replacing the old symbol-rate limits (300 bauds on most HF bands).

• A. Symbol rate and bandwidth are directly related: faster symbol changes spread the signal over more spectrum.
• C. Lower symbol rates need less bandwidth, not more.
• D. No fixed half-rate rule applies; occupied bandwidth depends on the modulation method and filtering as well as the symbol rate.

C. The sum and difference

A mixer combines its LO and RF inputs in a nonlinear circuit and produces signals at their sum and difference frequencies. With a 23 MHz LO and a 14 MHz signal, the output contains 37 MHz and 9 MHz, and a filter selects the one used as the IF.

• A. A mixer does not produce a frequency equal to the ratio of its inputs.
• B. A mixer does not produce the average of its input frequencies.
• D. A mixer multiplies the two waveforms, and that product contains the sum and difference frequencies; it does not produce a frequency equal to the product of the two frequencies.

A. Intermodulation

Intermodulation occurs when two or more signals pass through a nonlinear circuit, such as an overloaded amplifier or mixer, and combine to create unwanted new frequencies like 2F1 - F2. These spurious products can appear as signals that are not really on the air.

• B. Heterodyning is deliberate mixing to produce a wanted sum or difference frequency, such as an IF; intermodulation is the unwanted result.
• C. Detection recovers the information from a modulated signal (demodulation); it is not the creation of spurious products.
• D. Rolloff describes how fast a filter's response falls off outside its passband, not a mixing process.

C. 2F1-F2

The order of an intermodulation product is the sum of the multipliers on each frequency. For 2F1 - F2 that is 2 + 1 = 3, an odd (third-order) product.

• A. 5F1 - 3F2 has order 5 + 3 = 8, an even-order product.
• B. 3F1 - F2 has order 3 + 1 = 4, an even-order product.
• D. Both other products listed are even-order (orders 8 and 4), so not all the choices are odd-order.

A. WSPR

WSPR (Weak Signal Propagation Reporter) stations transmit low-power beacon signals carrying their call sign, location and power. Receiving stations upload what they decode to a public database, which maps where signals are being heard.

• B. MFSK16 is a keyboard-to-keyboard text mode for conversations, not a propagation beacon system.
• C. PSK31 is a keyboard-to-keyboard text mode for live conversations, not a beacon system.
• D. SSB-SC (single sideband, suppressed carrier) is a voice emission, not a digital mode.

C. Header

The header of a packet radio frame carries the routing and handling information, such as the source and destination call signs and any digipeater path. The data being sent follows the header.

• A. A packet frame has no "directory" field.
• B. The preamble comes before the frame and lets the receiver synchronize; it does not carry routing information.
• D. The trailer at the end of the frame carries the error-checking value, not the routing information.

C. A 5-bit code with additional start and stop bits

Baudot (ITA2) is a 5-bit teleprinter code; each character is sent as five data bits framed by a start bit and a stop bit. Part 97 describes it as "the 5-unit, start-stop, International Telegraph Alphabet No. 2" code (47 CFR 97.309(a)(1)).

• A. A 7-bit code with start, stop, and parity bits describes ASCII, not Baudot.
• B. Baudot has no error detection or correction; modes such as AMTOR and PACTOR add those.
• D. SELCAL (selective calling) and LISTEN are terms from AMTOR, not features of Baudot.

A. Request retransmission of the packet

In ARQ (automatic repeat request) modes, the receiving station checks each packet and replies ACK if it arrived intact or NAK (negative acknowledgment) if it did not. A NAK asks the sender to send that packet again.

• B. A packet received without error is answered with ACK, not NAK.
• C. Connection setup uses its own messages; a NAK is a request to resend a packet.
• D. A NAK refers to a single bad packet; it does not confirm that a whole file arrived.

B. The connection is dropped

An ARQ mode resends a packet each time it is not acknowledged, but only up to a set retry limit. When that limit is exceeded, the stations give up and drop the connection.

• A. A checksum is recomputed for each packet; repeated retries do not make it "overflow."
• C. Retries affect whether a packet gets through, not where it is routed.
• D. Failed retries do not change the character set; the encoding stays the same.

B. FT8

FT8 uses long symbols, a narrow 50 Hz signal and strong error correction, so it can decode signals far below the noise, down to about -20 dB signal-to-noise ratio measured in a 2.5 kHz bandwidth.

• A. MSK144 is a fast meteor-scatter mode that relies on short, relatively strong bursts reflected from meteor trails; it is not designed for continuous signals far below the noise.
• C. AMTOR is an older 100-baud FSK teleprinter mode that needs a reasonably strong signal.
• D. MFSK32 is a faster keyboard-to-keyboard mode; its higher speed means it needs a much stronger signal than FT8.

B. Upper case letters use longer Varicode bit sequences and thus slow down transmission

PSK31 sends characters in Varicode, where common characters get short bit patterns and rare ones get long patterns. Lowercase letters are the most common in text, so they are short, and uppercase letters take more bits and slow the transmission.

• A. Uppercase letters are not sent with more power; they only take more bits.
• C. Standard PSK31 (BPSK31) has no error correction; only the QPSK31 variant adds it.
• D. Because of its narrow bandwidth, PSK31 needs less power than RTTY for similar error rates, not more.

B. If one node fails, a packet may still reach its target station via an alternate node

In a mesh network, every node can relay traffic for the others, so there are usually several possible paths between two stations. If one node fails, the network routes packets around it through other nodes.

• A. Adding nodes does not make any one signal stronger; signal strength depends on power, antennas and path.
• C. Nodes linked directly over RF must share the same channel and bandwidth settings; the key property of a mesh is its alternate paths, not differing link frequencies.
• D. More nodes means more transmitters, which does not reduce out-of-band interference.

C. By transmitting redundant information with the data

Forward error correction adds redundant bits calculated from the data, so the receiver can detect and repair errors on its own without asking for a retransmission. Modes such as FT8 and QPSK31 use FEC.

• A. Controlling transmitter power changes signal strength; it does not let the receiver fix errors.
• B. Varicode is the character code of PSK31; it has no error correction.
• D. A single parity bit can detect some errors but cannot show which bit is wrong, so it cannot correct anything.

D. Mark and space

The two frequencies of an FSK signal are called mark and space, terms carried over from teleprinter systems. In amateur RTTY the mark and space are usually 170 Hz apart.

• A. Dot and dash are the elements of Morse code, not FSK frequencies.
• B. On and off describe on-off keying, as in CW, where the carrier is switched rather than shifted.
• C. High and low describe relative pitch, but the standard names for the two FSK frequencies are mark and space.

A. Varicode

PSK31 sends characters using Varicode, a variable-length code that gives frequently used characters short bit patterns. This keeps the average character short so text moves at typing speed with only 31.25 bauds.

• B. Viterbi is a decoding algorithm for convolutional error-correcting codes (used by QPSK31), not a character code.
• C. "Volumetric" is not a digital character code.
• D. All digital codes are made of binary bits; "binary" is not the name of the PSK31 character code.

D. Overmodulation

An overmodulated or overdriven data signal produces extra frequency components on either side of the wanted signal. On a waterfall they appear as faint vertical lines beside the main trace, a sign to reduce audio drive.

• A. Long-path propagation affects where a signal comes from and can add a slight echo; it does not create side lines on a waterfall.
• B. Backscatter produces weak, fluttery signals; it does not create side lines on a waterfall.
• C. Insufficient modulation gives a weak or missing trace, not extra lines beside the signal.

C. Frequency is horizontal, signal strength is intensity, time is vertical

A waterfall display puts frequency across the horizontal axis, scrolls time down the vertical axis, and shows signal strength as color or brightness. Each signal draws a vertical trace that shows its frequency over time.

• A. Frequency horizontal and signal strength vertical describes a spectrum (panadapter) display, which does not show time history.
• B. This swaps the axes: on a waterfall, frequency is horizontal and time is vertical.
• D. On a waterfall, frequency is horizontal, signal strength is shown as intensity, and time is vertical.

C. The signal-to-noise ratio is equivalent to +3dB in a 2.5 kHz bandwidth

FT8 reports are signal-to-noise ratios in decibels, measured relative to the noise in a 2.5 kHz bandwidth. A report of +3 means the signal is 3 dB above the noise in that bandwidth; most FT8 reports are negative because the mode decodes signals below the noise.

• A. The report compares the signal with the noise, not with an SSB signal, and +3 dB is a power ratio of about 2 (10^0.3 ≈ 2), not 3.
• B. FT8 reports are in decibels of signal-to-noise ratio, not S-meter units.
• D. "3 dB over S9" is an S-meter report for strong signals, not an FT8 signal-to-noise report.

D. DMR, D-STAR, and SystemFusion

DMR, D-STAR and System Fusion are digital voice systems: they digitize speech with a voice codec and send it as data, mostly on VHF and UHF through repeaters and networks.

• A. WSPR is a propagation beacon mode, MFSK16 is a text mode, and EasyPAL sends digital images (SSTV); none of them carries voice.
• B. FT8, FT4 and FST4 are weak-signal data modes that exchange short structured messages, not voice.
• C. Winlink, PACTOR II and PACTOR III carry email and other text messages, not voice.