Define modulation index as used in frequency modulation (FM);(2 marks)June/July 2020
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In frequency modulation (FM), the frequency of a carrier wave is varied in proportion to the amplitude of the input signal. The modulation index is a measure of the degree of frequency deviation of the carrier wave, and is defined as the ratio of the frequency deviation to the frequency of the modulating signal.
Mathematically, the modulation index is given by:
Modulation index = (Frequency deviation / Frequency of modulating signal)
For example, if the frequency deviation of a carrier wave is 50 kHz and the frequency of the modulating signal is 1 kHz, the modulation index would be 50. This means that the carrier wave’s frequency is being varied by 50 kHz in response to a 1 kHz modulating signal.
The modulation index is an important parameter in FM systems, as it determines the bandwidth of the transmitted signal and the clarity of the recovered signal. A higher modulation index results in a wider bandwidth and improved signal-to-noise ratio, but may also result in increased distortion.