Basically it has to do with the way hormones work or are triggered into action. It happens electrically. When the frequency is supplied via electricity it appears to actually mimic the action of melatonin. It may also destroy the hormone, but my experiments have not shown that. (When I run the frequency via my Scalar Craft 1A, I feel resonance - stuff vibrates and even blows up. When I run it via the F165 through contact mode, I don't feel resonance nor anything blowing up at all.)
Don't believe me? Derive the frequency for Human Growth Hormone, not too hard if you know how to multiply and divide. Run it via a wireless device, and then with a contact mode. You'll quickly see the huge difference in effect each has.
One destroys the hormone and the other mimics it...