# Extra Class Exam Question Pool

effective 7/01/2008 thru 6/30/2012

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E8B: Modulation and demodulation: modulation methods; modulation index and deviation ratio; pulse modulation; frequency and time division multiplexing

E8B01: What is the term for the ratio between the frequency deviation of an RF carrier wave, and the modulating frequency of its corresponding FM-phone signal?

Modulation index

FM compressibility

Quieting index

Percentage of modulation

E8B02: How does the modulation index of a phase-modulated emission vary with RF carrier frequency (the modulated frequency)?

It does not depend on the RF carrier frequency

It increases as the RF carrier frequency increases

It decreases as the RF carrier frequency increases

It varies with the square root of the RF carrier frequency

E8B03: What is the modulation index of an FM-phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency, when the modulating frequency is 1000 Hz?

3

0.3

3000

1000

E8B04: What is the modulation index of an FM-phone signal having a maximum carrier deviation of plus or minus 6 kHz when modulated with a 2-kHz modulating frequency?

3

6000

2000

1/3

E8B05: What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus-or-minus 5 kHz and accepting a maximum modulation rate of 3 kHz?

1.67

60

0.167

0.6

E8B06: What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz and accepting a maximum modulation frequency of 3.5 kHz?

2.14

0.214

0.47

47

E8B07: When using a pulse-width modulation system, why is the transmitter's peak power greater than its average power?

The signal duty cycle is less than 100%

The signal reaches peak amplitude only when voice modulated

The signal reaches peak amplitude only when voltage spikes are generated within the modulator

The signal reaches peak amplitude only when the pulses are also amplitude modulated

E8B08: What parameter does the modulating signal vary in a pulse-position modulation system?

The time at which each pulse occurs

The number of pulses per second

The amplitude of the pulses

The duration of the pulses

E8B09: How are the pulses of a pulse-modulated signal usually transmitted?

A pulse of relatively short duration is sent; a relatively long period of time separates each pulse

A pulse of relatively long duration is sent; a relatively short period of time separates each pulse

A group of short pulses are sent in a relatively short period of time; a relatively long period of time separates each group

A group of short pulses are sent in a relatively long period of time; a relatively short period of time separates each group

E8B10: What is meant by deviation ratio?

The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency

The ratio of the audio modulating frequency to the center carrier frequency

The ratio of the carrier center frequency to the audio modulating frequency

The ratio of the highest audio modulating frequency to the average audio modulating frequency

E8B11: Which of these methods can be used to combine several separate analog information streams into a single analog radio frequency signal?

Frequency division multiplexing

Frequency shift keying

A diversity combiner

Pulse compression

E8B12: Which of the following describes frequency division multiplexing?

Two or more information streams are merged into a "baseband", which then modulates the transmitter

The transmitted signal jumps from band to band at a predetermined rate

The transmitted signal is divided into packets of information

Two or more information streams are merged into a digital combiner, which then pulse position modulates the transmitter

E8B13: What is time division multiplexing?

Two or more signals are arranged to share discrete time slots of a digital data transmission

Two or more data streams are assigned to discrete sub-carriers on an FM transmitter

Two or more data streams share the same channel by transmitting time of transmission as the sub-carrier

Two or more signals are quadrature modulated to increase bandwidth efficiency

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