|[AMRadio] Odd signals in lower 80 meters|
A.R.S. - W5AMI
ars.w5ami at gmail.com
Sat Dec 23 05:10:16 EST 2006
On 12/22/06, D. Chester <k4kyv at charter.net> wrote:
> If it is a simple scrambling system that works by inverting the audio -
> making the lower frequencies come out high and vice versa, they could
> easily be decoded by copying as SSB in the opposite sideband position and
> offsetting the carrier frequency by whatever the tone frequency in the
> inverter is. When copying in the opposite sideband, that is exactly what
> happens - the lower frequencies come out the highest and vice versa. The
> audio inverter scramblers were designed for landline telephone use, and
> maybe for AM or FM radio use.
I think the audio is being inverted BEFORE being transmitted,
therefore simply selecting USB or LSB would make no difference. If
I'm thinking right, it would sound the same on any mode. Actually
these signals are likely even more complex than simple audio
inversion. Looking at the spectrum on these shows a very even
distribution of audio energy, no sloping at the high end, etc. I
suspect they are mixed with some reference signal, compressed,
normalized, etc., then transmitted.
Regardless, no matter what detection method I use, I can make no sense
of the signal.
Suburbia is where the developer bulldozes out the trees, then names
the streets after them. - Bill Vaughan
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