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Extra Class Exam Question Pool

effective 7/01/2016 thru 6/29/2020

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2016-E8C: Digital signals: digital communication modes; information rate vs bandwidth; error correction

2016-E8C01: 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



2016-E8C02: 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



2016-E8C03: 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



2016-E8C04: 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



2016-E8C05: 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



2016-E8C06: 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



2016-E8C07: 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



2016-E8C08: 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



2016-E8C09: Which is the name of a digital code where each preceding or following character changes by only one bit?

Gray code

Binary Coded Decimal Code

Extended Binary Coded Decimal Interchange Code

Excess 3 code



2016-E8C10: 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



2016-E8C11: 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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2016-E8B: Modulation and demodulation: modulation methods; modulation index and deviation ratio; frequency and time division multiplexing; Orthogonal Frequency Division Multiplexing
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2016-E8D: Keying defects and overmodulation of digital signals; digital codes; spread spectrum
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