Can't help you with that one, Bill. My frequency counter will not register, but an AM radio will pick up a tone that is obviously in the audio range. Quite a while back Dell talked about HID units operating in three different frequencies. I'd have to go back and check on it. I've seen ads from Asia that mention (pirated units?) 4-400 MHz and another mentions ultrasonic range.
"...The only instruments on the market that fully discriminate are the H.I.D. (Harmonic induction discrimination) These transmit & receive (3) timed, synchronized signals that respond to the Electron, Neutron, and Atomic Weight of the element. All other instruments on the market respond to the Electron only."
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