Question

Why the bandwidth of an FM signal is considered to be limited?

(a) because there can only be a finite number of sidebands

(b) because it is equal to the frequency deviation

(c) because it is band-limited at the receiver

(d) because the power in the outer sidebands is negligible

This question was addressed to me by my college professor while I was bunking the class.

My question is based upon Non Linear Device topic in division Side Band Techniques of Analog Communications

Answer 1

Right choice is (d) because the power in the outer sidebands is negligible

Explanation: In frequency modulation system, frequency of the carrier wave is varied in proportion with the instantaneous amplitude of the message signal, which is to be transmitted. IN Wideband FM, the number of sidebands are infinite. Thus, using Carson’s rule, the bandwidth of FM signal is kept limited considering the power impact of other sidebands negligible.