Question

What is the signal to noise ratio if the maximum allowable frequency deviation is 4kHz and the frequency deviation by noise is 156.42Hz?

(a) 0.0364

(b) 0.0391

(c) 25.75

(d) 20.45

This question was posed to me in semester exam.

The question is from Noise Suppression Effects of FM in division Amplitude & Frequency Modulation of Avionics

Answer 1

The correct choice is (c) 25.75

To explain: N/S = Frequency deviation by noise / maximum deviation = 156.42/4000 =0.0391

         S/N = (N/S)^-1=25.57.