or
Subelement G
Transmitters
Section 53
Oscillators & Modulators
What is the modulation index in an FM phone signal having a maximum frequency deviation of 3,000 Hz on either side of the carrier frequency when the modulating frequency is 1,000 Hz?
• 0.3
• 3,000
3
• 1,000

What is the modulation index in an FM phone signal having a maximum frequency deviation of 3,000 Hz on either side of the carrier frequency when the modulating frequency is 1,000 Hz?

3

Simply divide the deviation by the modulation frequency to arrive at the correct answer:

\begin{align} \text{modulation index} &= \frac{\text{deviation}}{\text{modulation frequency}} \\ &= \frac{3,000 \text{ Hz}}{1,000 \text{ Hz}} \\ &= 3 \end{align} --wileyj2956

In other words, the modulation index tells you how efficient the modulation is.

An index of 1 would mean that a 1000 Hz signal would cause a deviation of 1000 Hz on either side of the carrier. In this example, it takes a bandwidth of three times the modulating frequency on each side of the carrier to carry the information, a modulation index of 3.

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What is the modulation index of a FM phone transmitter producing a maximum carrier deviation of 6 kHz when modulated with a 2 kHz modulating frequency?
3
• 6,000
• 2,000
• 1

What is the modulation index of a FM phone transmitter producing a maximum carrier deviation of
6 kHz when modulated with a
2 kHz modulating frequency?

3

Simply divide the deviation by the modulation frequency to arrive at the correct answer:

\begin{align} \text{modulation index} &= \frac{\text{deviation}}{\text{modulation frequency}} \\ &= \frac{6\text{ kHz}}{2\text{ kHz}} \\ &= 3 \end{align} --wileyj2956

In other words, the modulation index tells you how efficient the modulation is.
An index of 1 would mean that a 1000 Hz signal would cause a deviation of 1000 Hz on either side of the carrier.

In this example, it takes a bandwidth of three times the modulating frequency on each side of the carrier to carry the information, a modulation index of 3.

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What is the total bandwidth of a FM phone transmission having a 5 kHz deviation and a 3 kHz modulating frequency?
• 3 kHz.
• 8 kHz.
• 5 kHz.
16 kHz.

What is the total bandwidth of a FM phone transmission having a 5 kHz deviation and a 3 kHz modulating frequency?

16 kHz

From wp2ahg:

5 kHz deviation on either side of the carrier frequency is a total of 10kHz.
Another 3 kHz on both side bands brings the total to 16 kHz.

(5 kHz x 2) + (3 kHz x 2) = 16 kHz

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How does the modulation index of a phase-modulated emission vary with RF carrier frequency?
It does not depend on the RF carrier frequency.
• Modulation index increases as the RF carrier frequency increases.
• It varies with the square root of the RF carrier frequency.
• It decreases as the RF carrier frequency increases.

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

It does not depend on the RF carrier frequency.

Note that it does not depend on the CARRIER frequency.

But, it DOES depend on the changes in the RF carrier frequency, as it varies with the square root of the RF carrier frequency.

For more information see the Direct Science site for the article Phase Modulation

Also, see the Montana Edu site for the pdf presentation on FM- Frequency Modulation PM - Phase Modulation

See Wikipedia's article on Amplitude modulation

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How can a single-sideband phone signal be generated?
• By driving a product detector with a DSB signal.
• By using a reactance modulator followed by a mixer.
• By using a loop modulator followed by a mixer.
By using a balanced modulator followed by a filter.

How can a single-sideband phone signal be generated?

By using a balanced modulator followed by a filter.

You can create a SSB by depressing one of the side bands, usually LSB, to leave only the USB upper side band. You have to suppress the carrier signal also. Suppressing the USB to use only LSB are less often used. The suppression can be done by the phasing or filtering method, or the Weaver's method.

See the Electronic Notes site for the article Single Sideband Modulation, SSB

Also see the Ham Radio School for the article Understanding Single Sideband (SSB)

Please see the Man Fas Org site for the article Single Side-Band Radio

See the Easy Tech Junkie site for the article What is a Balanced Modulator?

Also, see the Resources PCB Cadence site for the article Balanced Modulators in Analog Designs

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What is a balanced modulator?
• An FM modulator that produces a balanced deviation.
A modulator that produces a double sideband, suppressed carrier signal.
• A modulator that produces a single sideband, suppressed carrier signal.
• A modulator that produces a full carrier signal.

What is a balanced modulator?

A modulator that produces a double sideband, suppressed carrier signal.

There are two AM modulators, in balanced configuration, suppressing the carrier signal.

See the Easy Tech Junkie site for the article What is a Balanced Modulator?

Also, see the Resources PCB Cadence site for the article Balanced Modulators in Analog Designs

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