the original transmitter was 100mW based on the 27MHz CB radio band. As a result the signal could be received an a standard CB radio or walkie talkie. It was crystal controlled for one channel. The stock transmitter was a beeper that could be used for direction finding. There was a microphone option (which was a earphone) so you could hear what was happening on board, they also had a thermometer option and a photo cell that could be used to measure roll. It was available as a kit, or you could order it assembled for an additional charge. it used a square battery that I think was 6 volts, and was hard to find. I friend of mine built one was never able to get it to work.