Well, for RF transmission it is necessary to use some kind of encoding, like manchester. That way data slicer on the receiver end will never reach either end of supply but sit in the middle of it.

What you do is always send two bits for each bit of information, like 1 transmits as 10 and 0 as 01. Always 50% of duty cycle is maintained.

If you have more questions, try to search the picbasic forum on melabs site or e-mail me.

Ioannis