How is Forward Error Correction implemented?

  1. By the receiving station repeating each block of three data characters
  2. By transmitting a special algorithm to the receiving station along with the data characters
  3. By transmitting extra data that may be used to detect and correct transmission errors
  4. By varying the frequency shift of the transmitted signal according to a predefined algorithm


What is the definition of symbol rate in a digital transmission?

  1. The number of control characters in a message packet
  2. The duration of each bit in a message sent over the air
  3. The rate at which the waveform of a transmitted signal changes to convey information
  4. The number of characters carried per second by the station-to-station link


When performing phase shift keying, why is it advantageous to shift phase precisely at the zero crossing of the RF carrier?

  1. This results in the least possible transmitted bandwidth for the particular mode
  2. It is easier to demodulate with a conventional, non-synchronous detector
  3. It improves carrier suppression
  4. All of these choices are correct


What technique is used to minimize the bandwidth requirements of a PSK31 signal?

  1. Zero-sum character encoding
  2. Reed-Solomon character encoding
  3. Use of sinusoidal data pulses
  4. Use of trapezoidal data pulses


What is the necessary bandwidth of a 13-WPM international Morse code transmission?

  1. Approximately 13 Hz
  2. Approximately 26 Hz
  3. Approximately 52 Hz
  4. Approximately 104 Hz


What is the necessary bandwidth of a 170-hertz shift, 300-baud ASCII transmission?

  1. 0.1 Hz
  2. 0.3 kHz
  3. 0.5 kHz
  4. 1.0 kHz


What is the necessary bandwidth of a 4800-Hz frequency shift, 9600-baud ASCII FM transmission?

  1. 15.36 kHz
  2. 9.6 kHz
  3. 4.8 kHz
  4. 5.76 kHz


How does ARQ accomplish error correction?

  1. Special binary codes provide automatic correction
  2. Special polynomial codes provide automatic correction
  3. If errors are detected, redundant data is substituted
  4. If errors are detected, a retransmission is requested


Which is the name of a digital code where each preceding or following character changes by only one bit?

  1. Binary Coded Decimal Code
  2. Extended Binary Coded Decimal Interchange Code
  3. Excess 3 code
  4. Gray code


What is an advantage of Gray code in digital communications where symbols are transmitted as multiple bits

  1. It increases security
  2. It has more possible states than simple binary
  3. It has more resolution than simple binary
  4. It facilitates error detection


What is the relationship between symbol rate and baud?

  1. They are the same
  2. Baud is twice the symbol rate
  3. Symbol rate is only used for packet-based modes
  4. Baud is only used for RTTY