Path: utzoo!attcan!uunet!wang!tegra!vail
From: vail@tegra.COM (Johnathan Vail)
Newsgroups: sci.electronics
Subject: Re: Detecting Radar Detectors
Message-ID: <1285@atlas.tegra.COM>
Date: 15 Aug 90 15:20:37 GMT
References: <324@bally.Bally.COM> <229@dynasys.UUCP> <26c63bee-32e.10sci.electronics-1@vpnet.chi.il.us>
Organization: Tegra-Varityper, Inc., Billerica, MA
Lines: 45
In-reply-to: cgordon@vpnet.chi.il.us's message of 13 Aug 90 05:55:06 GMT

In article <26c63bee-32e.10sci.electronics-1@vpnet.chi.il.us> cgordon@vpnet.chi.il.us (Gordon Hlavenka) writes:

   >One other note here.  The way radars work is that waves are bounced off of
   >cars and the frequency is changed depending on how fast the car is going.
   >The radar measures the shift and approxiamates how fast the car was going
   >according to how much of a shift occurred.  Conceivably, you could build
   >a AECM unit that would detect the incoming frequency and broadcast back
   >some other frequency to fool the detector.  Of course, you would still have
   >the bounced frequency mixed in, so I'm not sure how well it would work.

   This is called a "gate stealer."

	A-   The military is already using it.
	B-   Civilian versions have been advertised as well.

   The civilian versions which I saw advertised (a couple years ago, no I don't
   have the address) called themselves "calibrators" for radar repair shop use,
   and the largest print in the ad was the warning that this equipment "will
   interfere with police radar units, causing erroneous low readings."

I think that this kind of device works by transmitting CW (continious
wave) pulses at a certain rate to spoof the counters that actually
measure the speed in the radar unit.  Although I understand that this
works to some extent, it should be easy to design around it and I have
heard that some of the newer units will detect when they are being
jammed.  And even if they work for some cases, they will be farther
off against moving radar.

The first first poster is talking about sending back a shifted signal.
This could work but is quite a bit harder to do.  Since the IF of some
units is in the middle of the 2M ham band, it might be possible to
spoof the detector at this frequency.

Anyway, given the extreme naughtiness of jammers and the very small
advantage of them I believe the best defence is awareness and a good
detector.   Still, it's fun to speculate about.

"Do policemen dream?
   ..Yes when they're fast asleep.
 And when policemen dream?
   ..It proves they're fast asleep" -- Robyn Hitchcock
 _____
|     | Johnathan Vail | n1dxg@tegra.com
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