From: jgd@dixie.com (John De Armond)
Newsgroups: rec.autos.driving,rec.autos
Subject: Re: Lasar radar again *sigh*
Date: 17 Apr 92 19:56:31 GMT
Article-I.D.: dixie.5-2j9bf
Organization: Dixie Communications Public Access.  The Mouth of the South.

jimf@centerline.com (Jim Frost) writes:

>wider angles.  That makes detectors much more practical although I'd
>still be surprised to find detection much farther out than .25 mile
>under good conditions -- that laser's still gotta be in the milliwatt
>range and IR doesn't carry that far if it's unfocused.  Still, that's
>better than nothing....

I'd not expect them to try to use it at 1/4 mile.  Not the least of
which because the pig could not reliably identify the car.  Where
this gun would be deadly would be in the typical urban bushwhack
situation where the pig waits until he sees the whites of your eyes
before firing.  It should be able to make an acquisition fairly
rapidly. but so can a cheap radar gun under the same circumnstance.


>BTW, my statement about "there's a bomb on the way" was intended to
>mean "if you're detecting LOS radiation it's already too late."  Even
>with multisecond lock-on times that's still the case, although a
>defocused fixed-frequency continual transmission laser will be lots
>easier to detect from reflection than what I expected the gun to have.

I can fairly reliably defeat my instant on radar gun with quick braking
so I'd expect to be able to defeat the LIDAR too.  Takes  practice and
attention.  One could even go so far as to say if one was not paying
enough attention to see the pig, perhaps a small speeding tax is in
order.

>A defocused IR beam means that sucker is going to be *very* unreliable
>in non-static situations.  That's better news than I had hoped for.

You got it.

>Do you know how the gun does velocity determination?  I'd expect it'd
>take distance measurements at timed intervals, except that if the
>source platform isn't completely stable you'd get extremely unreliable
>results (which would explain the "painting" technique you mention).

That is correct.  I've not gotten reliable information on the sample 
interval yet but I think it to be under one second.


>Note that by using a tunable laser rather than a fixed-frequency one
>most of the reliability problems would vanish: you could get reliable
>returns off of a much wider range of reflectors (this makes the gun
>less sensitive to car color).  With more reliable returns you'd be
>able to get faster lock times and less deviation due to gun motion.
>At this point the cost would be a major issue though.

Yes.  But consider that this gun sells for ~$4000 as it is.  Now 
factoring in the usual revenue harvesting equipment markup, they 
probably only have about $500 in it.  Not much room for sophistication.
Besides, the idiot media types who dutifully report the pig hype 
don't know a laser from a pig turd.  This gun is purely intimidation
with just a touch of Gee-whiz thrown in for bad taste.

>Thank you for a most enlightening response.

Thank you.  I'm pulling a couple of strings to see if I can get my
hands on one officially.  I'll report on it if I can.

John
-- 
John De Armond, WD4OQC        | What's the difference between Jane Fonda
Rapid Deployment System, Inc. | and Bill Clinton?  Hanoi Jane went to 
Marietta, Ga                  | Viet Nam.              
jgd@dixie.com                 | Need public access in Atl?  Write me.