General G8C: Digital protocols and displays
These are the 15 official questions in group G8C of the 2023–2027 General question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- G8C02Question 1
Which digital mode is used as a low-power beacon for assessing HF propagation?
- AWSPR Correct
- BMFSK16
- CPSK31
- DSSB-SC
Why: WSPR is a low-power beacon mode for checking HF propagation.
- G8C03Question 2
What part of a packet radio frame contains the routing and handling information?
- ADirectory
- BPreamble
- CHeader Correct
- DTrailer
Why: The header holds a packet's routing and handling information.
- G8C04Question 3
Which of the following describes Baudot code?
- AA 7-bit code with start, stop, and parity bits
- BA code using error detection and correction
- CA 5-bit code with additional start and stop bits Correct
- DA code using SELCAL and LISTEN
Why: Baudot is a 5-bit code with added start and stop bits.
- G8C05Question 4
In an ARQ mode, what is meant by a NAK response to a transmitted packet?
- ARequest retransmission of the packet Correct
- BPacket was received without error
- CReceiving station connected and ready for transmissions
- DEntire file received correctly
Why: A NAK asks for the packet to be retransmitted.
- G8C06Question 5
What action results from a failure to exchange information due to excessive transmission attempts when using an ARQ mode?
- AThe checksum overflows
- BThe connection is dropped Correct
- CPackets will be routed incorrectly
- DEncoding reverts to the default character set
Why: After too many failed attempts, the ARQ connection is dropped.
- G8C07Question 6
Which of the following narrow-band digital modes can receive signals with very low signal-to-noise ratios?
- AMSK144
- BFT8 Correct
- CAMTOR
- DMFSK32
Why: FT8 can decode signals at very low signal-to-noise ratios.
- G8C08Question 7
Which of the following statements is true about PSK31?
- AUpper case letters are sent with more power
- BUpper case letters use longer Varicode bit sequences and thus slow down transmission Correct
- CError correction is used to ensure accurate message reception
- DHigher power is needed as compared to RTTY for similar error rates
Why: Capital letters use longer Varicode sequences, which slows PSK31 down.
- G8C09Question 8
Which is true of mesh network microwave nodes?
- AHaving more nodes increases signal strengths
- BIf one node fails, a packet may still reach its target station via an alternate node Correct
- CLinks between two nodes in a network may have different frequencies and bandwidths
- DMore nodes reduce overall microwave out of band interference
Why: If one mesh node fails, packets can reach their target through another node.
- G8C10Question 9
How does forward error correction (FEC) allow the receiver to correct data errors?
- ABy controlling transmitter output power for optimum signal strength
- BBy using the Varicode character set
- CBy transmitting redundant information with the data Correct
- DBy using a parity bit with each character
Why: FEC sends redundant information so the receiver can correct errors.
- G8C11Question 10
How are the two separate frequencies of a Frequency Shift Keyed (FSK) signal identified?
- ADot and dash
- BOn and off
- CHigh and low
- DMark and space Correct
Why: FSK's two frequencies are called mark and space.
- G8C12Question 11
Which type of code is used for sending characters in a PSK31 signal?
- AVaricode Correct
- BViterbi
- CVolumetric
- DBinary
Why: PSK31 sends characters in Varicode.
- G8C13Question 12
What is indicated on a waterfall display by one or more vertical lines on either side of a data mode or RTTY signal?
- ALong path propagation
- BBackscatter propagation
- CInsufficient modulation
- DOvermodulation Correct
Why: Vertical lines beside a data signal on a waterfall mean overmodulation.
- G8C14Question 13
Which of the following describes a waterfall display?
- AFrequency is horizontal, signal strength is vertical, time is intensity
- BFrequency is vertical, signal strength is intensity, time is horizontal
- CFrequency is horizontal, signal strength is intensity, time is vertical Correct
- DFrequency is vertical, signal strength is horizontal, time is intensity
Why: A waterfall shows frequency horizontally, time vertically and strength as intensity.
- G8C15Question 14
What does an FT8 signal report of +3 mean?
- AThe signal is 3 times the noise level of an equivalent SSB signal
- BThe signal is S3 (weak signals)
- CThe signal-to-noise ratio is equivalent to +3dB in a 2.5 kHz bandwidth Correct
- DThe signal is 3 dB over S9
Why: An FT8 report of +3 means +3 dB SNR in a 2.5 kHz bandwidth.
- G8C16Question 15
Which of the following provide digital voice modes?
- AWSPR, MFSK16, and EasyPAL
- BFT8, FT4, and FST4
- CWinlink, PACTOR II, and PACTOR III
- DDMR, D-STAR, and SystemFusion Correct
Why: DMR, D-STAR and System Fusion are digital voice modes.