Key Topic 57: Frequency Modulation

Question 1

3-57H1: The deviation ratio is the:

A. Audio modulating frequency to the center carrier frequency.
B. Maximum carrier frequency deviation to the highest audio modulating frequency.
C. Carrier center frequency to the audio modulating frequency.
D. highest audio modulating frequency to the average audio modulating frequency.

Answer 1

B. Maximum carrier frequency deviation to the highest audio modulating frequency.

Question 2

3-57H2: What is the deviation ratio for an FM phone signal having a maximum frequency deviation of plus or minus 5 kHz and accepting a maximum modulation rate of 3 kHz?

A. 60
B. 0.16
C. 0.6
D. 1.66

Answer 2

D. 1.66

Question 3

3-57H3: What is the deviation ratio of an FM-phone signal having a maximum frequency wing of plus or minus 7.5 kHz and accepting a maximum modulation rate of 3.5 kHz?

A. 2.14
B. 0.214
C. 0.47
D. 47

Answer 3

A. 2.14

Question 4

3-57H4: How can an FM-phone signal be produced in a transmitter?

A. By modulating the supply voltage to a class-B amplifier.
B. By modulating the supply voltage to a class-C amplifier.
C. By using a balanced modulator.
D. By feeding the audio directly to the oscillator.

Answer 4

D. By feeding the audio directly to the oscillator.

Question 5

3-57H5: What is meant by the term modulation index?

A. The ratio between the deviation of a frequency modulated signal and the modulating frequency.
B. The processor index.
C. The FM signal-to-noise ratio
D. The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.

Answer 5

A. The ratio between the deviation of a frequency modulated signal and the modulating frequency.

Question 6

3-57H6: In an FM-phone signal, what is the term for the maximum deviation from the carrier frequency divided by the maximum audio modulating frequency?

A. Deviation index.
B. Modulation index.
C. Deviation ratio.
D. Modulation ratio.

Answer 6

C. Deviation ratio.