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Subelement ZLJ

Digital Systems

Section ZLJ30

Digital Systems

In the block diagram shown, the block designated "modem" is a

  • Correct Answer
    modulator/demodulator
  • modulation emphasis unit
  • Morse demodulator
  • MOSFET de-emphasis unit
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In the block diagram shown, the "modem"

  • monitors the demodulated signals
  • de-emphasises the modulated data
  • Correct Answer
    translates digital signals to and from audio signals
  • determines the modulation protocol
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The following can be adapted for use as a modem

  • an electronic keyer
  • a spare transceiver
  • a spare receiver
  • Correct Answer
    a computer sound-card
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The following are three digital communication modes

  • DSBSC, PACTOR, NBFM
  • AGC, FSK, Clover
  • PSK31, AFC, PSSN
  • Correct Answer
    AMTOR, PACTOR, PSK31
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In digital communications, FSK stands for

  • phase selection keying
  • final section keying
  • Correct Answer
    frequency shift keying
  • final signal keying
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In digital communications, BPSK stands for

  • Correct Answer
    binary phase shift keying
  • baseband polarity shift keying
  • band pass selective keying
  • burst pulse signal keying
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When your HF digital transmission is received with errors due to multi-path conditions, you should

  • increase transmitter power
  • Correct Answer
    reduce transmitted baud rate
  • reduce transmitter power
  • change frequency slightly

For the receiving end to be able to accurately decode the characters sent, the bits must be sent at a constant speed. The signalling speed of serial data transmissions on wires is measured in bits per second (bps), since the bits are always sent one at a time. However, the signalling speed on a radio link is not measured in bits, but in symbols per second (the unit of symbols/sec is the baud). The symbol is the basic modulated signalling entity on a radio link, and represents the state of each signalling interval. Each symbol may carry one or more (or even less) data bits, depending on the modulation technique. For RTTY, each symbol (a short duration of one tone or another) carries one data bit, so the speed in bps is the same as the baud rate.

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The letters BBS stand for

  • binary baud system
  • Correct Answer
    bulletin board system
  • basic binary selector
  • broadcast band stopper
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APRS is an adaptation of packet radio. APRS stands for

  • Correct Answer
    Automatic Packet Reporting System
  • Amateur Position Reporting System
  • Automatic Packet Relay System
  • Amateur Position Relay System
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The following communication mode is generally used for connecting to a VHF packet radio bulletin board

  • SSB
  • AM
  • Correct Answer
    FM
  • DSB
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