Question

Modulation index of an AM signal is ratio of __________ to the _______

(a) Peak carrier amplitude, Peak message signal amplitude

(b) Peak message signal amplitude, Peak carrier amplitude

(c) Carrier signal frequency, Message signal frequency

(d) Message signal frequency, Carrier signal frequency

This question was posed to me in an interview.

Question is taken from Amplitude Modulation in section Modulation Techniques for Mobile Radio of Wireless/Mobile

Answer 1

Right answer is (b) Peak message signal amplitude, Peak carrier amplitude

To explain: The modulation index k of an AM signal is defined as the ratio of the peak message signal amplitude to the peak carrier amplitude. The modulation index is often expressed as a percentage. It is also called percentage modulation.