Question

Differentiate between amplitude modulated (AM) and frequency modulated (FM) waves by drawing suitable diagrams. Why is FM signal preferred over AM signal?

Answer 1

When the amplitude of the carrier wave is changed in accordance with the intensity of the signal, it is called amplitude modulation.

When the frequency of the carrier wave is changed in accordance with the intensity of the signal, it is called frequency modulation.

Modulation of a carrier wave:
(a) a sinusoidal carrier wave;
(b) a modulating signal;
(c) amplitude modulation;
(d) frequency modulation

FM signal is preferred over AM signal because
(i) Various electrical machines and noises cause amplitude disturbance in the transmission of the amplitude-modulated waves. This makes the receptionnoisy. So, there is a need for Frequency Modulation which can reduce the noise factor.

(ii) Fidelity or audio quality of amplitude-modulated transmission is poor. This type of transmission is also not good for musical programs. There is a need to eliminate amplitude-sensitive noise. This is possible if we eliminate amplitude variation. In other words, there is a need to keep the amplitude of the carrier constant. This is precisely what we do in frequency modulation.