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Question:

A message signal of frequency 100MHz and peak voltage 100V is used to execute amplitude modulation on a carrier wave of frequency 300GHz and peak voltage 400V. The modulation index and difference between the two side band frequency are :

4;2×108Hz

0.25;2×108Hz

4;1×108Hz

0.25;1×108Hz

Solution:

Correct option is D. 0.25; 2×108Hz
fm=100MHz=108Hz, (Vm)0=100V, (Ve)0=400V
Modulation Index = (Vm)0/(Ve)0 = 100/400 = 1/4 = 0.25
Upper band frequency (UBF) = fe+fm
Lower band frequency (LBF) = fe−fm
∴UBF−LBF = 2fm = 2×108Hz