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From: Frederick Williams on 29 Mar 2010 17:24
I haven't heard much about television detector vans lately but we used
to be told that they could detect a television even if it was switched
off and they could even tell which room it was in.

How do such detectors work?

[I know nothing about electronics but my guess is that televisions
contain circuits that resonate at characteristic frequencies*. When
those circuits have electro magnetic radiation of those frequencies
directed at them, they resonate and re-emit those frequencies and such
emissions can be detected. Something like that.

* I'm using the phrase "characteristic frequencies" loosely.]

--
I can't go on, I'll go on.
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