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Subelement H
Modulation
Section 57
Frequency Modulation
The deviation ratio is the:
  • Audio modulating frequency to the center carrier frequency.
  • Correct Answer
    Maximum carrier frequency deviation to the highest audio modulating frequency.
  • Carrier center frequency to the audio modulating frequency.
  • Highest audio modulating frequency to the average audio modulating frequency.

The deviation ratio is the:

Maximum carrier frequency deviation to the highest audio modulating frequency.

The above is the definition of the deviation ratio. Maximum frequency deviation explanation is below.


From K4AGO
TIP: It is the only answer that has 'deviation' in it.

In FM modulation, the two primary parameters of interest are deviation ratio and modulation index. Deviation ratio is the ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.

The deviation ratio of an FM-phone signal having a maximum frequency swing of plus-or-minus 5 kHz when the maximum modulation frequency is 3 kHz is 1.67.

The deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz when the maximum modulation frequency is 3.5 kHz is 2.14.


Definition from the International Telecommunications Union, ITU-R SM.1268-4:

"Frequency deviation: In the case of frequency modulation, the deviation of the frequency from the frequency of the unmodulated carrier f0."

For more information, please see ITU INT site, for pdf report titled Recommendation ITU-R SM.1268-4 Method of measuring the maximum frequency deviation of FM broadcast emissions at monitoring stations

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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?
  • 60
  • 0.16
  • 0.6
  • Correct Answer
    1.66

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?

1.66

From wp2ahg:

Deviation Ratio is the maximum frequency deviation divided by the maximum modulation rate.

\[\frac{5\text{ kHz}}{3\text{ kHz}} = 1.66\]

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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 rate of 3.5 kHz?
  • Correct Answer
    2.14
  • 0.214
  • 0.47
  • 47

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 rate of 3.5 kHz?

2.14

From wp2ahg:

\[\frac{7.5\text{ kHz}}{3.5\text{ kHz}} = 2.14\]

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How can an FM-phone signal be produced in a transmitter?
  • By modulating the supply voltage to a class-B amplifier.
  • By modulating the supply voltage to a class-C amplifier.
  • By using a balanced modulator.
  • Correct Answer
    By feeding the audio directly to the oscillator.

How can an FM-phone signal be produced in a transmitter?

By feeding the audio directly to the oscillator.

For more info, please see Wikipedia's article on Electronic oscillator

Also, please see the Electrical 4 U site for the article on Oscillators: What Are They? (Definition, Types, & Applications)

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What is meant by the term modulation index?
  • Correct Answer
    The ratio between the deviation of a frequency modulated signal and the modulating frequency.
  • The processor index.
  • The FM signal-to-noise ratio.
  • The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.

What is meant by the term modulation index?

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

Modulation Index:

\[\frac{M}{A} = \text{ m}\]

M is the maximum peak difference from unmodulated waves.

A is the carrier amplitude

For more info, please see Electronics Notes site for the article on Amplitude Modulation, AM Index & Modulation Depth

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In an FM-phone signal, what is the term for the maximum deviation from the carrier frequency divided by the maximum audio modulating frequency?
  • Deviation index.
  • Modulation index.
  • Correct Answer
    Deviation ratio.
  • Modulation ratio.

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

Deviation ratio.

From K4AGO TIP: It is the only answer that has 'deviation' in it.

In FM modulation, the two primary parameters of interest are deviation ratio and modulation index. Deviation ratio is the ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.

The deviation ratio of an FM-phone signal having a maximum frequency swing of plus-or-minus 5 kHz when the maximum modulation frequency is 3 kHz is 1.67.

The deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz when the maximum modulation frequency is 3.5 kHz is 2.14.


Definition from the International Telecommunications Union, ITU-R SM.1268-4:

"Frequency deviation: In the case of frequency modulation, the deviation of the frequency from the frequency of the unmodulated carrier f0."

For more information, please see ITU INT site, for pdf report titled Recommendation ITU-R SM.1268-4 Method of measuring the maximum frequency deviation of FM broadcast emissions at monitoring stations

Last edited by markadlerdallas. Register to edit

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