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From: advax@reg.triumf.ca (A.Daviel)
Newsgroups: sci.electronics
Subject: Re: Radar detector DETECTORS?
Date: 6 Apr 1993 16:13 PST
Organization: TRIUMF: Tri-University Meson Facility
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Message-ID: <6APR199316135249@reg.triumf.ca>
References: <1993Apr06.173031.9793@vdoe386.vak12ed.edu> <1pslckINNmn0@matt.ksu.ksu.edu>
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In article <1pslckINNmn0@matt.ksu.ksu.edu>, nhowland@matt.ksu.ksu.edu (Neal Patrick Howland) writes...
> 
>From what I understand about radar dectectors all they are is a passive
>device much like the radio in your car.  They work as an antenna picking
>up that radar signals that the radar gun sends out.  Therefore there would
>be no way of detecting a radar detector any more than there would be of
>detecting whether some one had a radio in their car.  
> 
From my rather rusty knowledge of radio, most radio receivers use a superhet 
circuit, so that the incoming signal is mixed with a local oscillator, giving 
a fixed intermediate frequency (IF) that is more easily amplified. The
detector detectors work by picking up IF re-radiated from your radar 
detector. In Britain, where one has/used to pay for a TV licence, there 
are/were TV detector vans prowling the streets, looking for people who hadn't 
paid their licence fee. They had a couple of long solenoid antennae on the
roof, and I believe could triangulate an operating TV from the IF. 

I wonder how much of the IF is radiated back from the detector antenna, and 
how much from the rest of the module. It might be worth putting the detector 
in a proper RF shielded enclosure.

--
 Andrew Daviel, Vancouver, Canada <advax@triumf.ca>
  finger advax@reg.triumf.ca for PGP key
