For a radio controlled system (a radio controlled car for example) what are the main components of the circuit (As in a block diagram kind of thing)?

I know you will have switches on the handset, an oscillator for a carrier wave, and then something to modulate a signal onto that, then at the reciever a filter, amplifier, and something to demodulate the signal. Then maybe a ADC and a microcontroller to control the motors/servos?

How is it usually done?

 

Have you checked here and the links therein?

John