If you wanted to transmit stealhily, you'd put modulation power in the difference between
the sidebands, ie. the AM stereo difference channel. So you'd modulate one up and one
down, so a receiver would pick off the same audio signal with or without your modulation.

You decode it by listening asymetrically to the sidebands, eg. SSB or even synchronous
detection on a single sideband, or AM detuned nearly to distortion.

In fact WFAN 660 NYC had a 120 Hz hum on its signal for a couple of months that was
only in this difference channel, that apparently went undetected by even the engineers;
and WOWO 1190 Ft Wayne I think had some strange low frequency modulation on theirs the
same way a couple of days ago (can't check them now because there's a thousand stations
on the frequency, at 4am) audible only if you receive a single one of the sidebands.
--
Ron Hardin


On the internet, nobody knows you're a jerk.