Question

The antenna current of an AM transmitter is 8 A when only the carrier signal is transmitted. What is the antenna current when the carrier signal is modulated by sinusoidal signal V(t) = 1.4 sin (2π × 500t) with modulation index 0.8 ?
1. 3.2 A
2. 7.2 A
3. 9.2 A
4. 11.2 A

Answer 1

Correct Answer - Option 3 : 9.2 A

Concept:

In AM total transmitted power is given by,

 \(P_t=P_c(1+\frac{μ^2}{2}) \)

Where P_t → total transmitted power, P_c→ carrier power, μ =modulation index 

Power can be given as P = I²R

\(I_t^2 R= I_c^2R \sqrt{1+\frac {\mu^2}{2}} \)

where, I_t→total antenna current, I_C→ unmodulated current

Calculation:

Given: I_c  8A 

\(I_t=8\sqrt {(1+(0.8^2)/2)} \)

I_t = 9.2 A