Frequency Modulation

In Frequency Modulation, the strength (amplitude) of the radio frequency wave is fixed and its actual frequency is varied in time with the changing frequency and amplitude of the audio signal.

The top picture represents an audio wave which is to modulate a radio frequency and the lower picture shows how the modulated RF wave changes frequency in sympathy with the audio. The greater the audio amplitude, the higher the deviation in the radio frequency and the higher the audio frequency, the greater the rate at which the radio frequency changes.

Whatever the modulation method, we now have a radio frequency wave which is able to travel in space acting as a 'carrier' for an audio signal which can normally only travel through wires. Once amplified, this signal can be fed to an antenna and launched into the atmosphere to be picked up by any waiting receiver!