Question

What is the ratio of the shift produced by the noise to the maximum allowed deviation if the modulating frequency is 300Hz and the phase shift by noise is 25° and the maximum allowable deviation is 5kHz?

(a) 1.3

(b) 0.530

(c) 0.153

(d) 0.0261

This question was addressed to me at a job interview.

This question is from Noise Suppression Effects of FM in section Amplitude & Frequency Modulation of Avionics

Answer 1

Correct answer is (d) 0.0261

Explanation: δ=ɸ(fm)= 0.436(300)=130.89Hz

        Frequency deviation by noise / maximum deviation = 130.89/5000=0.0261.