Question

In satellite communication, frequency modulation is used because satellite channel has
1. High modulation index
2. Small bandwidth and negligible noise
3. Large bandwidth and severe noise immunity
4. Maximum bandwidth and minimum noise

Answer 1

Correct Answer - Option 3 : Large bandwidth and severe noise immunity

In the case of FM,

Bandwith is large and noise immunity is high that's why it is used in satellite communication.

The bandwidth of FM:

B.W of FM = 2 (β + 1) f_m

where β = modulation index

∵ since β is generally ≫ 1 so FM B.W ≫ 2 f_m

whereas in AM B.W is 2 f_m, in DSB-SC BW is 2 f_m, SSB-SC BW is f_m.

So we can see the B.W of FM is large, as compared to other schemes.

FOM of FM:

The figure of merit is defined as

\(FOM = \frac{{\left( {SNR} \right)\;o/p}}{{\left( {SNR} \right)\;i/p}}\) 

FOM ↑ → SNR o/p ↑ → Noise ↓

In the case of FM, \(FOM = \frac{3}{2}{\beta ^2} \gg 1\) whereas in the case of DSB-SC and SSB-SC FOM is 1.

So noise immunity of FOM is so high.