2016-E8C: Digital signals: digital communication modes; information rate vs bandwidth; error correction
How is Forward Error Correction implemented?
By transmitting extra data that may be used to detect and correct transmission errors
By the receiving station repeating each block of three data characters
By transmitting a special algorithm to the receiving station along with the data characters
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?
The rate at which the waveform of a transmitted signal changes to convey information
The number of control characters in a message packet
The duration of each bit in a message sent over the air
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?
This results in the least possible transmitted bandwidth for the particular mode
It is easier to demodulate with a conventional, non-synchronous detector
It improves carrier suppression
All of these choices are correct
What technique is used to minimize the bandwidth requirements of a PSK31 signal?
Use of sinusoidal data pulses
Zero-sum character encoding
Reed-Solomon character encoding
Use of trapezoidal data pulses
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
What is the necessary bandwidth of a 170-hertz shift, 300-baud ASCII transmission?
What is the necessary bandwidth of a 4800-Hz frequency shift, 9600-baud ASCII FM transmission?
How does ARQ accomplish error correction?
If errors are detected, a retransmission is requested
Special binary codes provide automatic correction
Special polynomial codes provide automatic correction
If errors are detected, redundant data is substituted
Which is the name of a digital code where each preceding or following character changes by only one bit?
Binary Coded Decimal Code
Extended Binary Coded Decimal Interchange Code
Excess 3 code
What is an advantage of Gray code in digital communications where symbols are transmitted as multiple bits
It facilitates error detection
It increases security
It has more possible states than simple binary
It has more resolution than simple binary
What is the relationship between symbol rate and baud?
They are the same
Baud is twice the symbol rate
Symbol rate is only used for packet-based modes
Baud is only used for RTTY
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