Fred - you can program several different frequencies in the 433 or 434 band. If I'm not mistaken, the 100 or 500 in FM100/FM500 means it's capable of receiving that many different frequencies in its respective band. In reality, you'd want to space them out a bit so nothing overlaps. I believe 434 is more common with falconers and, if I'm not mistaken, some other commercial entity is using 433. Again, I'm sure Ron or Tom will come along and right the ship, again, but, if my understanding is half-ass accurate, I'm pretty sure with 5 (hz??) of separation, you could still use 100 different transmitters with a FM500, all on different frequencies.

The reason I'm going to buy a FM500 in 434 is to maximize my ability to help other falconers in the area who are on UHF.

Hopefully I'm not too far off the mark because this has been my logic behind planning to buy the FM500 in 434. I'm definitely looking forward to some input from Ron/Tom now as it might save me some money!