[Milsurplus] DFing receiver LOs and truck ignition radiation

[mikea]

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