"The
trick was to modulate the ultrasound at sonic rates. The directivity of the
ultra-sound speaker was intact. And the ear would hear the sonic modulation
directly."
That's not the trick.
W0RI is right. You have to *demodulate* the 432MHz signal.
With ultrasound, it's easy. You just crank up the ultrasound
intensity until the air's response to the ultrasound signal is
nonlinear, and you get demodulation right there in the air!
With RF, you'd need *at least* enough ERP to turn the air to plasma,
and that's no guarantee that you'd demodulate... I suspect you
probably have to drive the *plasma* pretty hard to get useful
nonlinearity... and I don't know off the top of my head if there'd be
any useful radiation.
Maybe if you could get enough field intensity in the ionosphere... but
there's just no way that any ham could generate this amount of
power... look at what they have to do at HAARP to get any ionospheric
modification *at all*.
Nonlinear effects in propagation media are really fascinating, but
unfortunately for this idea, propagation in a vacuum or air is just
totally linear.
73,
Dan
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