Amateur Extra E8D: Spread spectrum, keying and data codes
These are the 11 official questions in group E8D of the 2024–2028 Amateur Extra 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.
Learn E8D step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.
- E8D01Question 1
Why are received spread spectrum signals resistant to interference?
- ASignals not using the spread spectrum algorithm are suppressed in the receiver Correct
- BThe high power used by a spread spectrum transmitter keeps its signal from being easily overpowered
- CBuilt-in error correction codes minimize interference
- DIf the receiver detects interference, it will signal the transmitter to change frequencies
Why: The receiver suppresses any signal that doesn't use the spreading algorithm.
- E8D02Question 2
What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?
- AFrequency hopping
- BDirect sequence Correct
- CBinary phase-shift keying
- DPhase compandored spread spectrum
Why: Direct sequence shifts the carrier's phase with a fast bit stream.
- E8D03Question 3
Which describes spread spectrum frequency hopping?
- AIf interference is detected by the receiver, it will signal the transmitter to change frequencies
- BRF signals are clipped to generate a wide band of harmonics which provides redundancy to correct errors
- CA binary bit stream is used to shift the phase of an RF carrier very rapidly in a pseudorandom sequence
- DRapidly varying the frequency of a transmitted signal according to a pseudorandom sequence Correct
Why: Frequency hopping changes frequency rapidly in a pseudorandom sequence.
- E8D04Question 4
What is the primary effect of extremely short rise or fall time on a CW signal?
- AMore difficult to copy
- BThe generation of RF harmonics
- CThe generation of key clicks Correct
- DMore difficult to tune
Why: Very short rise or fall times create key clicks.
- E8D05Question 5
What is the most common method of reducing key clicks?
- AIncrease keying waveform rise and fall times Correct
- BInsert low-pass filters at the transmitter output
- CReduce keying waveform rise and fall times
- DInsert high-pass filters at the transmitter output
Why: Lengthening the rise and fall times reduces key clicks.
- E8D06Question 6
What is the advantage of including parity bits in ASCII characters?
- AFaster transmission rate
- BSignal-to-noise ratio is improved
- CA larger character set is available
- DSome types of errors can be detected Correct
Why: Parity bits detect some kinds of errors.
- E8D07Question 7
What is a common cause of overmodulation of AFSK signals?
- AExcessive numbers of retries
- BExcessive frequency deviation
- CBit errors in the modem
- DExcessive transmit audio levels Correct
Why: Too much transmit audio overmodulates AFSK.
- E8D08Question 8
What parameter evaluates distortion of an AFSK signal caused by excessive input audio levels?
- ASignal-to-noise ratio
- BBaud error rate
- CRepeat Request Rate (RRR)
- DIntermodulation Distortion (IMD) Correct
Why: IMD measures AFSK distortion from too much audio.
- E8D09Question 9
What is considered an acceptable maximum IMD level for an idling PSK signal?
- A+5 dB
- B+10 dB
- C+15 dB
- D-30 dB Correct
Why: −30 dB IMD is an acceptable maximum for idling PSK.
- E8D10Question 10
What are some of the differences between the Baudot digital code and ASCII?
- ABaudot uses 4 data bits per character, ASCII uses 7 or 8; Baudot uses 1 character as a letters/figures shift code, ASCII has no letters/figures code
- BBaudot uses 5 data bits per character, ASCII uses 7 or 8; Baudot uses 2 characters as letters/figures shift codes, ASCII has no letters/figures shift code Correct
- CBaudot uses 6 data bits per character, ASCII uses 7 or 8; Baudot has no letters/figures shift code, ASCII uses 2 letters/figures shift codes
- DBaudot uses 7 data bits per character, ASCII uses 8; Baudot has no letters/figures shift code, ASCII uses 2 letters/figures shift codes
Why: Baudot uses 5 bits with letters/figures shifts; ASCII uses 7 or 8 bits with no shifts.
- E8D11Question 11
What is one advantage of using ASCII code for data communications?
- AIt includes built-in error correction features
- BIt contains fewer information bits per character than any other code
- CIt is possible to transmit both uppercase and lowercase text Correct
- DIt uses one character as a shift code to send numeric and special characters
Why: ASCII can send both upper- and lower-case text.
Learn E8D step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.