Question

What bandwidth is needed for an FM signal that has a peak deviation of +3 kHz and handles audio signals from 200 Hz to 5 kHz ?
1. 6 kHz
2. 16 kHz
3. 10 kHz
4. 9.6 kHz

Answer 1

Correct Answer - Option 3 : 10 kHz

Concept:

According to Carson’s rule, if β>1

BW is given by

BW = 2(β + 1)f_m 

Where,

 f_m = highest modulating frequency

Δ­­_f = β.f_m

Where,

 Δ_f  = peak deviation and

 β = Modulation index of FM

if β<1 then it is called NBFM and for NBFM bandwidth is 2fm.

Calculation:

Given:

Δ_f  = 3 kHz, f_m = 5 kHz

therefore β = 0.6 which is less than one. hence the given signal is NBFM

so  B.W = 2f_m which is equal to 10K Hz.