Extra-Study/pages/E8D.md

E8D Keying defects and overmodulation of digital signals; digital codes; spread spectrum

• E8D01 (A) Why are received spread spectrum signals resistant to interference? #card
  • A. Signals not using the spread spectrum algorithm are suppressed in the receiver
  • B. The high power used by a spread spectrum transmitter keeps its signal from being easily overpowered
  • C. Built-in error correction codes minimize interference
  • D. If the receiver detects interference, it will signal the transmitter to change frequencies
• E8D02 (B) What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier? #card
  • A. Frequency hopping
  • B. Direct sequence
  • C. Binary phase-shift keying
  • D. Phase compandored spread spectrum
• E8D03 (D) Which describes spread spectrum frequency hopping? #card
  • A. If interference is detected by the receiver, it will signal the transmitter to change frequencies
  • B. RF signals are clipped to generate a wide band of harmonics which provides redundancy to correct errors
  • C. A binary bit stream is used to shift the phase of an RF carrier very rapidly in a pseudorandom sequence
  • D. Rapidly varying the frequency of a transmitted signal according to a pseudorandom sequence
• E8D04 (C) What is the primary effect of extremely short rise or fall time on a CW signal? #card
  • A. More difficult to copy
  • B. The generation of RF harmonics
  • C. The generation of key clicks
  • D. More difficult to tune
• E8D05 (A) What is the most common method of reducing key clicks? #card
  • A. Increase keying waveform rise and fall times
  • B. Insert low-pass filters at the transmitter output
  • C. Reduce keying waveform rise and fall times
  • D. Insert high-pass filters at the transmitter output
• E8D06 (D) What is the advantage of including parity bits in ASCII characters? #card
  • A. Faster transmission rate
  • B. Signal-to-noise ratio is improved
  • C. A larger character set is available
  • D. Some types of errors can be detected
• E8D07 (D) What is a common cause of overmodulation of AFSK signals? #card
  • A. Excessive numbers of retries
  • B. Excessive frequency deviation
  • C. Bit errors in the modem
  • D. Excessive transmit audio levels
• E8D08 (D) What parameter evaluates distortion of an AFSK signal caused by excessive input audio levels? #card
  • A. Signal-to-noise ratio
  • B. Baud error rate
  • C. Repeat Request Rate (RRR)
  • D. Intermodulation Distortion (IMD)
• E8D09 (D) What is considered an acceptable maximum IMD level for an idling PSK signal? #card
  • A. +5 dB
  • B. +10 dB
  • C. +15 dB
  • D. -30 dB
• E8D10 (B) What are some of the differences between the Baudot digital code and ASCII? #card
  • A. Baudot 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
  • B. Baudot 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
  • C. Baudot 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
  • D. Baudot uses 7 data bits per character, ASCII uses 8; Baudot has no letters/figures shift code, ASCII uses 2 letters/figures shift codes
• E8D11 (C) What is one advantage of using ASCII code for data communications? #card
  • A. It includes built-in error correction features
  • B. It contains fewer information bits per character than any other code
  • C. It is possible to transmit both uppercase and lowercase text
  • D. It uses one character as a shift code to send numeric and special characters