Calculation of frequency deviation in Frequency Modulation

The audio signal having frequency 500Hz and voltage 2.6V, shows a deviation of 5.2KHz in a Frequency Modulation system. If the audio signal voltage changes to 8.6V, calculate the new deviation obtained.

Options:

17.2 KHz
19.6 KHz
25.6 KHz
14.6 KHz

Correct Answer: 17.2 KHz

Explanation:

Deviation in FM is given by Δf= k_f * A_m
Therefore, k_f= Δf/ A_m
= 5.2/2.6
= 2
When voltage changes to 8.6V= A_m’
New frequency deviation Δf’ = k_f * A_m’
= 2* 8.6
= 17.2 KHz