Question

An AM signal is represented by x(t) = (30 + 2Sin(700πt)) Cos(2πt x 10^2t)V. What is the value of modulation index?

(a) 0.7

(b) 0.066

(c) 0.341

(d) 0.916

This question was addressed to me in class test.

Question is from Power Relations in AM Waves in section Amplitude Modulation of Analog Communications

Answer 1

Right option is (b) 0.066

Explanation: Given equation can be written as 30(1 + 0.066 Sin(700πt)).

Comparing it with general AM equation, s(t) = Ac(1 + mAm cos(wmt)) cos(wct),

Where, Ac = Amplitude of Carrier Signal, Am = Amplitude of Message Signal

 m=Modulation Index

So modulation index(m) = 0.066.