Path: utzoo!mnetor!uunet!husc6!bloom-beacon!mgm.mit.edu!wolfgang
From: wolfgang@mgm.mit.edu (Wolfgang Rupprecht)
Newsgroups: sci.electronics
Subject: Re: radar countermeasures
Message-ID: <3615@bloom-beacon.MIT.EDU>
Date: 10 Mar 88 01:52:44 GMT
References: <1101@silver.bacs.indiana.edu> <2203@saturn.ucsc.edu> <3606@killer.UUCP> <1988Mar7.233054.235@utzoo.uucp>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: wolfgang@mgm.mit.edu (Wolfgang Rupprecht)
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In article <1988Mar7.233054.235@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>Radar signal return follows an inverse-fourth-power law, inverse-square
>outbound and again inbound, assuming diffuse reflection.  Radar detection
>is only inverse-square, since the signal doesn't make a round trip.  Other
>things being equal (detection technology, size of antenna, etc.), this
>means that a radar signal can always be detected from well beyond the
>effective range of the radar itself.  Of course, other things aren't always
>equal, and if the radar isn't in steady use, a range advantage may not mean
>a time advantage.

This observation of inverse-fourth power for diffuse reflection vs.
distance is brilliant. (I wish I'd thought of that!)

I don't think that this is the typical limitation a police radar is
operating under, though. For the most part, cops have gotten more
clever and aren't "shining" their radars down long stretches of
straight roads anymore. This gives people with radar detectors too
much warning. (And leads to the situation that Henry describes, where
detection will always win.) Many of the radar traps now seem to
illuminate the road at an oblique angle around rocks or bridges, where
the difference in longitudinal distance for being in the radar "shade"
to being in the full flux is only a few tens of feet. This doesn't
give the driver much reaction time. One saving grace in a situation
like this is that other cars ahead of you, will act as radar mirrors,
often reflecting the signal "around the corner" for you. Nothing like 
keeping a few "passive scouts" in front of you!



Wolfgang Rupprecht	ARPA:  wolfgang@mgm.mit.edu (IP 18.82.0.114)
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