An AM transmitter has an un-modulated carrier power of 10 kW. It can be modulated by a sinusoidal modulating voltage to a maximum depth of 40%, without overload. If the maximum modulation index is reduced to 30%, what is the extent up to which the modulated carrier power can be increased without overloading?

Ans

Given that Pc = 10kW

Modulation index µ = 0.4

Total transmitted power

\[ P_t = P_c \left(1 + \frac{\mu^2}{2}\right) = 10 \times 10^3 \left(1 + \frac{0.16}{2}\right) = 10.8 \, \text{kW} \]

Now the effective modulation index

\[ m_a = \sqrt{m_{a1}^2 + m_{a2}^2} = \sqrt{0.16 + 0.09} = 0.5 \]

The total radiated power

\[ P_t = P_c \left(1 + \frac{m^2}{2}\right) \]

\[ P_t = P_c \left(1 + \frac{0.25}{2}\right) = 10 \times 10^3 \times 1.125 \]

Hence Pt = 11.25kW

Hence modulated carrier power is increased by amount of 11.25 - 10.08 = 1.17kW



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