Section 3
Transmitters and Receivers

Microphone amplifiers and modulators

3E1 Recall that the microphone amplifier amplifies the signal from the microphone to the level required to drive the modulator and limits the audio frequencies to those required for communication.

An excessively high level of input audio signal from the audio amplifier into the modulator results in an excessive amplitude modulated signal. For instance, if you shout into the microphone, then instead of a louder sound of your voice in the receiver being heard then only a much distorted voice will be heard and depending upon the extent of distortion may nor may not be understood at all. The additional ADVERSE effect of an excessive input, is thus overmodulation that interference to adjacent channels / frequencies may well occur in an Amplitude modulated transmitter.

Recall the need to ensure that the microphone gain control (where fitted) is correctly adjusted.

The problem of excessive input can be prevented by the CORRECT use of the Microphone gain control where fitted to the transmitter.

The origin of some of the text on this page is from the RSGB with additions by the web master