I just tried the system outside. Using 4 emitters at a peak current of 120mA (one could go to 200mA without problems) the connection works at up to 35m *outside* at 3.00pm (right now). We have heavy clouds here at the moment, but no rain. When putting the rx offset to about 45-60° from the direction where the tx is the distance goes down to about the half. You have to loosely point the tx to the rx for these results. Inside a normal living room it doesn't matter where the rx and tx point to, the connection will always be up.
This is good news IMHO! I'm sure these results can be further improved by using more emitters, two or three sensors, and higher current. The tx uses a duty cycle of about 8%, so 2 sets of emitters driven by 200mA peak each will result in only 32mA constant current draw, which can easily be provided by the tx battery, also because the original rf tx is deactivated by pulling out the crystal.
Now I *have to* build a flyable rx!
only one PIC is needed! The sensor contains all the electronics to make a nice digital signal from the IR signal. This signal is fed directly into one PIC that contains Andy's code (slightly modified by me). That's all!