# AM signal - Transmission efficiency & Synchronous detection

## What is the maximum transmission efficiency of an AM signal?

a.) 64.44%
b.) 33.33%
c.) 56.66%
d.) 75.55%

Explanation:

The transmission efficiency (η) of AM wave is defined as the percentage of total power contributed by side bands of the AM signal. The maximum transmission efficiency of an AM signal is 33.33%, i.e., only one third of the total transmitted power is carried by the side bands in an AM wave. The remaining two third of the total transmitted power gets wasted.

## In synchronous detection of AM signal

a.) Carrier is locally generated
b.) Passed through a low pass filter
c.) The original signal is recovered
d.) All of the above

Correct Answer : d) All of the above

Explanation:

In synchronous detection of AM signal, the carrier signal is locally generated and then passed through a low pass filter. At the output of the low pass filter, the original modulating signal is recovered. The synchronous detection requires the generation of carrier at the receiver also. So additional circuitry is required at the receiver.