Jay Rusgrove wrote:
Possibly the old NBVM (narrow band voice modulation) system debeloped by Dr.
R.J. Harris and
published in QST Nov. & Dec. 1978. There was a limited production run of
commercial units, and a
hard sell to the ARRL and commercial SSB users followed, however the concept
never caught on.
Imagine there are still units floating around.
A brief overview of the system can be found here:
http://www.qsl.net/vk5br/NarBandVoice.htm
Details are in the QST articles. Being in on the original testing, I can say it
was darn near
impossible to get any intelligence from the 'folded over' signal.
Jay W1VD
There were some rigs used back in the late 70's and early 80's, where
the police departments became more aware of those citizens that were
listening on scanners at home, to keep abreast with what was going on in
their community... and they knew (know) that the crooks use them too, to
try to stay a step ahead of the law.
In Southern California, Pomona, specifically, there was a 'code' they
used to go to the 'scrambled' mode; 'Gold'.
"Unit so-and-so, meet unit so-and-so on city-wide tack 2, 'gold'."
Gold was the 'code' to 'go scrambled', so that no one else (outside of
those officers who went and listened with their so-equipped rigs).
A little circuit inside the rig, activated by a miniature toggle switch
was all that was required.
I've head these signals on 75m in the evening hours, and I thought that
was -exactly- how it sounded. If the high-end response is replaced by
the low-end response, there won't be a high-end roll-off... you'd hear
the equivalant of the low-end roll-off, and pretty much, it's fairly
dramatic at around 100hz, in those commercial communication services.
Like most of y'all, though, I had never heard of that system being used
on SSB.
Let the Pumkin Pie be served! Pour the Egg Nog, and warm the filaments!
It's time to celebrate!
CHRISTMAS (_or_insert_your_celebrated_holiday_here_) Is here! It's time
to enjoy the fellowship and commraderie of your fellow AM'ers.
It's RADIO TIME!
--
Ho Ho, Mo-Fo!
73 = Best Regards,
-Geoff/W5OMR
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