Re: TV Detecotrs (was They don't take bookings for individuals on Friday, Satruday and Sundays)

On Wed, 30 Nov 2005 12:02:21 +0000, Simon Brooke
<simon@xxxxxxxxxxxxxx> wrote:

>
>Cathode ray tubes emit enough radiation during the raster scan for the
>image they are showing to be fairly reliably reconstructed through a
>brisk wall, so detector vans certainly used to work very well. All the
>processing involved in driving an LCD panel also generates a certain
>amount of radiation, but whether it's coherent enough to reconstruct the
>picture and thus detect the difference between a computer display and
>something displaying broadcast TV I don't know.

I do not believe the detector vans tried to get the picture. I was
told there was a detectable pulse when the CRT retraced and the vans
picked up that. They could tell which channel was being watched
because this pulse was in sync with the transmitter.

Apparently the pulse can also be detected on the national grid when a
popular television program is on. Everybody adding in their little
pulses synchronised to the local transmitter.

I would imagine that detection has become harder for the simple vans I
described for a number of reasons. Modern CRT tellys are better
screened. Digital TV is not syncronised to the transmitter. Other
CRTs. And some people accept the compromises of LCD and Plasma
screens as you said.

Of course what I heard could be complete rubbish.

.

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