> At your very low data rate and very short required range, I think that
> simply pulsing a PIC pin at RF frequencies might work. This would have
> the advantage of a VERY low parts count. However, it would have the
> disadvantage of requiring you to run your PIC at frequencies which are
> much higher than usual for such a low-power circuit.

A really crazy idea:

Clock the PIC AT your RF frequency! Make the CLOCK PCB traces LONG
and use THEM as antenna!!!  Put the PIC asleep for a 0 (18ms), or
stay running a loop to transmit a 1.

Using RC clock, the startup time is very short.