Question
What is the modulation index of an FM phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency if the highest modulating frequency is 1000 Hz?
Answer Options
- A) 3
- B) 0.3
- C) 6
- D) 0.6
Correct Answer: A
Explanation
The modulation index (\beta) for an FM signal is calculated by dividing the maximum frequency deviation (\Delta f) by the maximum modulating frequency (f_m). This ratio is used to determine the necessary bandwidth of the signal using Carson’s Rule.
Given the maximum frequency deviation (\Delta f) is 3000 Hz and the highest modulating frequency (f_m) is 1000 Hz, the modulation index is \beta = \Delta f / f_m = 3000 Hz / 1000 Hz = \mathbf{3}. This is an example of a wideband FM signal, as the index is greater than 1.
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