Answer Posted / syncopator
If we radiate a simple r.f. carrier it conveys no information other than the fact that its transmitter is working. Not much use is it?
The name "carrier" suggests that it is capable of carrying information.
The information is applied to the carrier so that the carrier's characteristics are changed. It is these changes which represent the information being carried.
Changes to the carrier's characteristics are called modulation.
The two most common ways that the information can change its carrier's characteristic are by altering the amplitude of the carrier (it should come as no surprise to learn that this is called amplitude modulation, abbreviated to a.m.), and by altering the frequency of the carrier (which, of course, is f.m.)
The process of recovering the information imposed upon a carrier (the modulation) is called demodulation or detection.
Exactly the same processes are encountered in audio.
If an audio note has its amplitude varied (modulated) to and fro (up and down) it is called tremolo - in r.f. we call it a.m. (it's the same thing).
If an audio note has its frequency varied back and forth, it is called vibrato - in r.f. we call it f.m. (it's the same thing).
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