[Milsurplus] DFing receiver LOs and truck ignition radiation

[J. Forster]

Actually, this could work.

Consider a lot of cars on the road. An individual LO might well not be
detectable easily, but a LOT of LOs might make a fairly easily detectable
spectral bump. If all the LOs radiated equally, it's actually a pretty
clever way of the cars "voting" for the most popular station.

Best,
-John

===============


> On Fri, Dec 04, 2009 at 10:42:31AM -0500, Ray Fantini wrote:
>> Some years back I worked for a marketing research company and they
>> tried to develop a system to automatically detect and log what
>> channels people were watching. We did not waste time on trying to
>> detect LO radiation due to most televisions built after the seventies
>> radiate so little that it's not practical to receive a millo watt
>> signal but we did use the output of the sweep stage of the TV that we
>> were able to detect being most old analog sets developed a good six
>> or eight watts of signal in their sweep stages at 15.75 Kc. You can
>> compare the phase of the sweep signal to the phase of horizontal sync
>> pulse of the broadcaster and determine if someone was watching the
>> same channel. System was useless because in a urban environment there
>> are so many sets you can't tell anything. This is why I am always so
>> doubtful of the whole LO detecting story. The BBC still says they have
>> TV detection vans that can now detect PC TV tuner cards but many are
>> starting to question their ability to do this. There are no technical
>> papers or equipment published or marketed for this function. Look
>> at this web site for pictures of different detection vans thru the
>> years: http://www.oobject.com/category/sinister-bbc-spy-vehicles/ and
>> maybe you can speculate what the antennas do. The art of deterrent
>> is producing the fear in your opponents mind, real or imagined.
>
> Back around October 2000 to May 2001, when I was working in the Redwood
> City, Ca. area off and on, there were some billboards which sensed the
> LO freq. of car radios and changed their messages accordingly. I don't
> know exactly how they worked, though I suspect they looked for the
> strongest peak in the LO spectrum and worked from there. They made the
> newspapers for a while, with people writing about privacy violations and
> suchlike. Enough milliwatts add up to a pretty detectable signal, and I
> *know* I've wound up listening to other folks' leaky FM radios when they
> pulled up next to me.
>
> --
> Mike Andrews, W5EGO
> mikea at mikea.ath.cx
> Tired old sysadmin
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