E8C: Digital signals: digital communications modes; CW; information rate vs. bandwidth; spread-spectrum communications; modulation methods
E8C01:
Which one of the following digital codes consists of elements having unequal length?
Morse code
ASCII
AX.25
Baudot
E8C02:
What are some of the differences between the Baudot digital code and ASCII?
Baudot uses five data bits per character, ASCII uses seven; Baudot uses two characters as shift codes, ASCII has no shift code
Baudot uses four data bits per character, ASCII uses seven; Baudot uses one character as a shift code, ASCII has no shift code
Baudot uses six data bits per character, ASCII uses seven; Baudot has no shift code, ASCII uses two characters as shift codes
Baudot uses seven data bits per character, ASCII uses eight; Baudot has no shift code, ASCII uses two characters as shift codes
E8C03:
What is one advantage of using the ASCII code for data communications?
It is possible to transmit both upper and lower case text
It includes built-in error-correction features
It contains fewer information bits per character than any other code
It uses one character as a shift code to send numeric and special characters
E8C05:
What technique is used to minimize the bandwidth requirements of a PSK-31 signal?
Use of sinusoidal data pulses
Zero-sum character encoding
Reed-Solomon character encoding
Use of trapezoidal data pulses
E8C06:
What is the necessary bandwidth of a 13-WPM international Morse code transmission?
Approximately 52 Hz
Approximately 13 Hz
Approximately 26 Hz
Approximately 104 Hz
E8C07:
What is the necessary bandwidth of a 170-hertz shift, 300-baud ASCII transmission?
0.5 kHz
0.1 Hz
0.3 kHz
1.0 kHz
E8C08:
What is the necessary bandwidth of a 4800-Hz frequency shift, 9600-baud ASCII FM transmission?
15.36 kHz
9.6 kHz
4.8 kHz
5.76 kHz
E8C09:
What term describes a wide-bandwidth communications system in which the transmitted carrier frequency varies according to some predetermined sequence?
Spread-spectrum communication
Amplitude compandored single sideband
AMTOR
Time-domain frequency modulation
E8C10:
Which of these techniques causes a digital signal to appear as wide-band noise to a conventional receiver?
Spread-spectrum
Independent sideband
Regenerative detection
Exponential addition
E8C11:
What spread-spectrum communications technique alters the center frequency of a conventional carrier many times per second in accordance with a pseudo-random list of channels?
Frequency hopping
Direct sequence
Time-domain frequency modulation
Frequency compandored spread-spectrum
E8C12:
What spread-spectrum communications technique uses a high speed binary bit stream to shift the phase of an RF carrier?
Direct sequence
Frequency hopping
Binary phase-shift keying
Phase compandored spread-spectrum
E8C13:
What makes spread-spectrum communications resistant to interference?
Only signals using the correct spreading sequence are received
Interfering signals are removed by a frequency-agile crystal filter
Spread-spectrum transmitters use much higher power than conventional carrier-frequency transmitters
Spread-spectrum transmitters can hunt for the best carrier frequency to use within a given RF spectrum
E8C14:
What is the advantage of including a parity bit with an ASCII character stream?
Some types of errors can be detected
Faster transmission rate
The signal can overpower interfering signals
Foreign language characters can be sent
E8C15:
What is one advantage of using JT-65 coding?
Virtually perfect decoding of signals well below the noise
Uses only a 65 Hz bandwidth
Easily copied by ear if necessary
Permits fast-scan TV transmissions over narrow bandwidth
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