In the cave, the signal is not likely to get out, and if the signal cannot get out, then its range does not go beyond the cave, and if the signal cannot be heard farther than a certain distance, does this not fall under part 15 of the FCC regs. Therfore in a cave, anything would be legal, except maybe transmitting on the lower end of the RF spectrum. So now freeband transitters, export radios, $200 chinese FM broadcast transmitters and other assorted nasties would have a legit market. HMMM, the underground loophole. Could this be reality or just a another crazy idea i thought up?