pls suggest a prac ckt for freq shift keying mod & demod

hi there,
i am looking for a simple circuit for frequency shift keying modulator(transmitter) and demodulator(receiver).
any practically operational circuit for the above design will be very helpful.
do suggest one...
do post your replies with a cicuit diagram...
i will appreciate any help...
see ya later,
venkatesh

Have you looked at **broken link removed**?

The National Semiconductor application note, AN46 show how to design an FSK receiver (demodulator). You can download it from www.nsc.com. The LM555 data sheet shows how to modulate it for PPM, if you modulate with a square wave it becomes FSK.