Question

A message signal of frequency 100 MHz and peak voltage 100 V is used to execute amplitude modulation on a carrier wave of frequency 300 GHz and peak voltage 400 V. The modulation index and difference between the two side band frequencies are:
(A) 4 ; 2 × 10⁸ Hz (B) 4 ; 1 × 10⁸ Hz
(C) 0.25 ; 1 × 10⁸ Hz (D) 0.25 ; 2 × 10⁸ Hz

Answer 1

•According to the question, amessage signal of frequency 100 MHz and peak voltage 100 V is used to execute amplitude modulation on a carrier wave of frequency 300 GHz and peak voltage 400 V.

• So,Fm = 100MHz = 10^8 MHz

(Vm)o = 100V , ( Ve)o =400 V

So the modulation index = (Vm)o /( Ve)o

= 100/400 = 1/4 = 0.25

UBF or Upper Band Frequency = Fe + Fm

LBF or Lower Band Frequency= Fe – Fm

so,the difference between the two side band frequencies are [UBF — LBF] = 2Fm = 2× 10 ^8 Hz

So, the answer is (D) 0.25 ; 2 × 10⁸ Hz

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