Modulation index of FM

Calculate the modulation index in an FM signal when f_m (modulating frequency) is 250Hz and Δf (frequency deviation) is 5KHz.

Options:

a) 20
b) 35
c) 50
d) 75

Correct Answer: a) 20

Explanation:

Modulation index is the measure of how much the modulation parameter changes from its un modulated value. The modulation index of FM is given by
μ = frequency deviation/ modulating frequency
= Δf/ f_m
Where Δf is the peak frequency deviation i.e. the deviation in the instantaneous value of the frequency with modulating signal.
f_m is the value of modulating frequency
μ =5000/250
= 20