Date: Fri, 17 May 2002 07:33:24 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Radar detector
In-Reply-To: <005f01c1fd0d$3a8f8150$6401a8c0@tdaoffice>
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At 03:09 PM 5/16/2002, developtrust wrote:
>I know a man who sold radar detectors. The fact is (he said) that none of
>them worked. Snake oil would work better.
>
>William
I see you haven't owned one... <g> There are various distinctions:
Passive vs superheterodyne -- the former have disappeared completely
AFAIK. The Escort from Cincinnati Microwave was one of the first examples
of the superhet type, if that helps give you a time line. Passive types
aren't very good.
Frequency coverage -- early speed radar used continuously-transmitting
X-band (10.525 GHz) with considerable power (8 watts or more). These units
aren't in common use any more but I've encountered them in Michigan and
southern New Jersey -- each time detectable from miles away on clear
road. Modern radar is either K-band (24.150 GHz) or Ka-band (33.4-36
GHz). Both use much lower power and many/most can be used in a mode where
the unit doesn't transmit until the officer is looking at you and pushes
the button. Modern radars can determine speed in a fraction of a second,
so if you happen to be the guy in front the detector will light up like a
pinball machine and tell you that you've just been bagged. If there's
someone ahead of you the detector will often/usually detect the splash off
that vehicle when it gets read, and you have a chance to briefly evaluate
your life choices before you get the direct beam. The latest development
isn't strictly radar at all -- it's LIDAR; I forget the acronym but it's a
laser device that does successive range-finding using an infrared laser and
calculates speed (very rapidly) from that. Unlike radar which has a
noticeable beam spread, LIDAR has very little spread and uses a gunsight so
that the officer can be quite specific (under most circumstances) about
precisely which vehicle he was pointing at. Police love to use these from
overpasses at about a half-mile range, with a chase car(s) hidden
below. They don't work well in rain and fog, but they also are very hard
to detect -- the beam bounces off the vehicle ahead like a flashlight beam,
and there's an excellent chance that the reflections aren't headed your
way. Modern detectors will detect all these bands, including laser -- but
the laser part is much more likely to tell you that you've just been nailed
than that you're about to be.
Camouflage -- a working radar detector like all superheterodyne receivers
contains a small transmitter, and the police have a device that listens for
it. Of course that device, being a superhet receiver itself makes its own
little noise; and fancier detectors will listen for that and shut down when
they detect it. They aren't working at that point, but at least you don't
get bagged for having one in the car (in case that's not permitted where
you are). Also, permitted or not they do make the polizei soggy and hard
to light, so it's good politics not to have little things stuck to your
windshield when you're talking to The Man.
Active interferers -- there are various devices that attempt to confuse the
machine at the other end. Generally highly illegal, I'd hate to get caught
with one. The Federal government has a very distinct notion that the
famous American right to receive freely from the airwaves does *not*
include the right to transmit freely; lasers aren't covered by that but at
least some states have laws against interfering with police speed-detection
by any method whether active or passive.
False alarms -- these things are just little radio receivers. They don't
know there's a policeman on the other end of that signal; quite often it's
a supermarket door opener. There are some patterns the user can observe
that help distinguish speed radar, but false alarms are a fact of life.
Sociology -- the police, not being stupid, have become aware that
triggering off a speed radar is normally followed by flashing brake
lights. This is so effective that highway departments have taken to
mounting K-band transmitters on construction warning signs, because it
makes the people slow down. If you see a (powered) construction sign with
what looks like a little silver floodlight hanging from the bottom, that's
what it is. The radar-detector people, eager to show that they are a
Social Good, have leaped on this with glad cries and developed a set of
signal codes to be transmitted by ambulances, fire trucks, construction
sites etc. etc. The detector I use believes in 64 distinct safety codes
(deer in road -- deer in rut -- rutting deer in road -- Bambi -- possible
grease spot under next overpass etc) and will speak them aloud. If you
have time on your hands it will speak them all one after another.
Overall -- in about 20 years of using these things I have unquestionably
saved several tickets, as well as numerous detections when I was perfectly
legal. I've also unquestionably been nailed several times with the needle
on the wrong side of the line, but I was within the officer's tolerance
that day and didn't get stopped. I've also listened to about 20,000 false
alarms. Not sure whether the detectors have cost more than the tickets
would have (I think less), but I don't have any points on my license.
cheers
david
--
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
