Question
What is the modulation index of an FM signal?
Answer Options
- A) The ratio of frequency deviation to modulating signal frequency
- B) The ratio of modulating signal amplitude to frequency deviation
- C) The modulating signal frequency divided by the bandwidth of the transmitted signal
- D) The bandwidth of the transmitted signal divided by the modulating signal frequency
Correct Answer: A
Explanation
The modulation index (\beta) is the key parameter used to characterize and calculate the total bandwidth of an FM (Frequency Modulation) signal. It quantifies the degree of modulation applied to the carrier and is directly related to the complexity of the signal’s spectrum.
The modulation index is defined as the ratio of frequency deviation to modulating signal frequency. Frequency deviation (\Delta f) is the maximum instantaneous shift of the carrier frequency, and the modulating frequency (f_m) is the highest audio frequency component present in the baseband signal. This ratio, \beta = \Delta f / f_m, is used with Carson’s Rule to determine the total required bandwidth for the FM signal.
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