Question

Draw a block diagram of a detector for AM signal and show, using necessary processes and the waveforms, how the original message signal is detected from the input AM wave.

Answer 1

When a message is received, it gets attenuated through the channel. Therefore, receiving antenna is to be followed by an amplifier and a detector. The carrier frequency is usually changed to a lower frequency in an intermediate frequency (IF) stage. The detected signal may not be strong enough to be made use of and, hence, is required to be amplified.

In order to obtain the original message signal m(t) of angular frequency, a simple method is used which is shown below in the form of a block diagram.

When the received modulated signal is passed through a rectifier, an envelope signal is produced. This envelope signal is the message signal. In order to retrieve the message, the signal is passed through an envelope detector.