I was looking on the net for the wireless systems mentioned on this board and found a Kima KS-110. It's used for remote stereo listing. It looks like a perfect candidate for a caller. The product description states a 1000 foot range. They sell for about 49. They even can operate on 3 AA batteries with no modifications. It looks like an older US robotic's product. The frequency range looks good at 20-20K. Has anyone tried using one of these in a Home made caller?
Link to Kima KS-110
Link to Kima KS-110