Question

A modulating signal is amplified by a 80% efficiency amplifier before being combined with a 20 kW carrier to generate an AM signal. The required DC input power to the amplifier, for the system to operate at 100% modulation, would be

(a) 5 kW

(b) 8.46 kW

(c) 12.5 kW

(d) 6.25 kW

I had been asked this question by my school principal while I was bunking the class.

My doubt stems from Amplitde Modulation topic in section EDC Overview of Electronic Devices & Circuits

Answer 1

Correct answer is (c) 12.5 kW

The best I can explain: Pi = Pt -Pc = 30 – 20 = 10 kW. DC input = 10/0.8 or 12.5 kW.