Subelement G: Transmitters— Topic 53: Oscillators & Modulators
Question 3-53G1
Element 3 (GROL)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?
Explanation
The modulation index (m) for a frequency modulated (FM) signal is calculated by dividing the maximum frequency deviation (Δf) by the maximum modulating frequency (fm). It represents the ratio of how much the carrier frequency shifts to the frequency of the modulating signal.
Using the given values:
* Maximum frequency deviation (Δf) = 3,000 Hz
* Modulating frequency (fm) = 1,000 Hz
The formula is:
m = Δf / fm
m = 3,000 Hz / 1,000 Hz
m = 3
Therefore, the modulation index is 3.
Option A (0.3) would result from an incorrect calculation, such as dividing the modulating frequency by the deviation.
Option B (3,000) is the frequency deviation itself, not the modulation index.
Option D (1,000) is the modulating frequency itself, not the modulation index.
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