[Wolves] Digital Radio (OFFTOPIC TV detectors)

[Neil Woolford]

>Does standby keep the crt warm and would that emit rf radiation that could
>be detected? Or does it still decode the signal just keeping the tube dark
>which might be detectable.




>I remember hearing that they could actually detect what channel you were
>watching so I suspect some sort of van Eck phreaking
>(http://whatis.techtarget.com/definition/0,289893,sid9_gci550525,00.html) is
>used but that should only get TVs that are on.
>
>
>chris

My distant days as a trainee Radio and TV Mechanic (that's the City and 
Guilds' description of the course) come in handy here!

Basically, all practical modern (since about 1940) analogue receivers have 
what is known as a 'local oscillator' which produces a steady radio 
frequency signal (a 'tone' if you like).  The frequency of this tone is 
related to the frequency of the broadcast the apparatus is tuned to.  This 
locally generated signal, and certain harmonics and beat products from the 
interaction between it and the received signal, is indeed detectable in the 
manner of van Eck phreaking.  And yes, the fundamental frequency of the 
signals indicates which channel the set is tuned to.  Unplugged and fully 
powered down is *not* detectable, as there is then no local signal.

I had a tour of a detector van in the very early 70s and one of the antenna 
systems was directional enough to allow location of a set to within a 
couple of yards if they took two or three shots at it.  (RDF or goniometry 
are the terms for this technology I think.)  However, most of the work is 
actually done by parsing the databases and footslogging from door to 
door.  (My late mother's house accumulated a lot of mail from them in the 
year after she died, and I have had a man come to the door to enquire why I 
had no licence.  [Because I don't have a TV should anyone be interested...])

Neil
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