what is the different between class A,B,C amplifier?

what is the different between class A,B,C amplifier? Why class C amplifier always use in RF circuits?
THX:)

Hi
Very basic.
It has something to due with the linearity of the drive.

Class A is full linear operation
Class B is driving the transistor 50% of the time
Class C is driven less than 50%.

What you gain is more efficiency, but at the cost of more distortion(harmonics).''

Regards

http://www.highfrequencyelectronics....%20part%202%22