Radar Gun Fundamentals

[Clifford Heath]

These are the same cops who shot 81 rounds and only hit the suspect 27
times at point blank range. How do you think they can hit a license
plate at half a mile and never miss?.

And that's assuming that the sighting laser still points in
vaguely the same direction as the speed laser...

 

[Homer J Simpson]

They can miss the intended target and score a direct hit on the wrong
one?

You can with radar - they were notorious for that.

 

[JoeBloe]

Complete crap. Parallax error is error in measured speed due to the
radar looking out from the side of the road at an angle.

Wrong. Nice try though. In auto radars, it is where the radar
acquires the fastest article in its field of view, but the cop
incorrectly chooses the wrong vehicle as being the vehicle that was
traveling at the clocked speed. It is the very reason that radars are
successfully fought in the courts of many states. Cop pops a radar
scan down twenty cars on a highway, but picks you as the one that was
pegging the radar gun. Lots of room for human error there.

Looking down a road on an angle changes the operation of the device
not one iota. It takes a reading in its FOV rather quickly, and it
does it well, regardless of whether you are approaching it, receeding
from it, or crossing its field.

 

[Richard Henry]

Looking down a road on an angle changes the operation of the device
not one iota. It takes a reading in its FOV rather quickly, and it
does it well, regardless of whether you are approaching it, receeding
from it, or crossing its field.

Does the radar automatically correct for the angle?

 

[Joel Kolstad]

Plus, who can tell whether someone's using an optical chaff
generator. It isn't hard to flash an LED or uncollimated LD
of the right wavelength, flash length, and period, to
completely baffle the laser gun so it either can't get a
reading at all, or gets a wrong one.

I would expect that a LIDAR gun uses something similar to a direct-sequence
spread spectrum pulse of LED flashes that it correlates to back on the
receiving side. That would make it rather difficult to jam!

Anyone know for certain?

 

[Jim Thompson]

Does the radar automatically correct for the angle?

JoeBloe is ignorant ;-)

...Jim Thompson

 

[[email protected]]

I would expect that a LIDAR gun uses something similar to a direct-sequence
spread spectrum pulse of LED flashes that it correlates to back on the
receiving side. That would make it rather difficult to jam!

Anyone know for certain?

One of the car magazines did some real world testing and the best
"jammer" was a set of very hot driving lights. It drives the preamp
into saturation. Once the car gets close enough the gun can more
selectvely choose a spot to look at and it gets a reading.

Legally the cop is supposed to identify a suspected speeder and then
use the guin to verify his suspicion. We know that is not really the
way it works, particularly with a radar trap. A guy with a good radar
detector can easily "frame" an innocent driver by slowing down at the
right time and making the guy going the legal speed look like the bad
guy.

 

[Charlie Edmondson]

Does the radar automatically correct for the angle?

Of course not. It doesn't know what the angle is! It can only measure
direct closure (or its opposite) between the gun and the target. So,
unless you are directly in front of, or behind the target, you get a
certain amount of error. However, that error is in the targets favor,
so it doesn't help you in court! And a laser can still get the wrong
vehicle, it depends on how good the aim of the user is...

Charlie

 

[Joel Kolstad]

One of the car magazines did some real world testing and the best
"jammer" was a set of very hot driving lights. It drives the preamp
into saturation.

Yeah, that's understandable. I'd think the guns would have an overload
detector (just as some contemporary radar guns have jammer detectors),
although perhaps with a *pulsed* set of ultra-bright lights you could avoid
the overload detector triggering (since presumably it needs some filtering to
prevent falsing when, e.g., the cop swing the gun around and it briefly stares
into a headlight or the sun or whatever).

A guy with a good radar
detector can easily "frame" an innocent driver by slowing down at the
right time and making the guy going the legal speed look like the bad
guy.

True enough, I suppose... although it's at least a little harder than a cop
simply claiming outright you were speeding and the court taking his word
alone?

 

[Rich Grise, Plainclothes Hippie]

Shakespeare said "For 'tis the sport to have the engineer
Hoist with his own petar" (Hamlet III iv). But that was a long time
ago 1604?).

What part of the body is the petar(d)? And have you ever been hoisted by
yours? That must really hurt. =:-O

Thanks,
Rich

 

[Rich Grise]

... With a good IF you can differntiate male
and female hip swing.

http://home.gwi.net/~jdebell/pe/cj/v20-1.htm

Cheers!
Rich

 

[Rich Grise]

On Wed, 25 Oct 2006 14:40:35 GMT, "Homer J Simpson"


Most of the radar in SW Florida will be shot from a moving deputy
cruiser while he is running other calls. They shoot you coming at them
and come get you if a speeding ticket is more important than his next
call.

There are a couple of spots in Whittier where you're on the honor system -
they have those "your speed is" displays (solar-powered) in a couple of
school zones, or where the limit changes from 45 to 30 or so.

Very fascinating displays - they're those little mechanical flipper
pixels (a little flapper, black on one side and yellow on the other),
with an interesting twist - if the number is over, say, 35 (or whatever
it's set at), the yellow pixels flash orange.

Cheers!
Rich

 

[Richard Henry]

What part of the body is the petar(d)? And have you ever been hoisted by
yours? That must really hurt. =:-O

A petard is a portable bomb with a "slow" fuse attached, used in the
case cited by Shakespeare to blow a hole in a fortification. Typically
an engineer would dig a tunnel under a wall, place his petard, and
light it, and then try to get away before the explosion. Sometimes the
wall came down, sometimes the engineer went up.

 

[mark]

What part of the body is the petar(d)? And have you ever been hoisted by
yours? That must really hurt. =:-O

Thanks,
Rich

You've got to read the classics more Rich. I believe a petard is either a
type of morter/cannon or similar to a satchel charge. (gee, maybe I should
read the classics more myself and find out)
M Walter

 

[mark]

http://home.gwi.net/~jdebell/pe/cj/v20-1.htm

Cheers!
Rich

Interesting anecdote I read. Someone circa 1940 built just such a device. It
was for an electronic exposition. The engineer's were worried some Scotish
officer would show up in kilts.

M Walter

 

[Rich Grise, Plainclothes Hippie]

A petard is a portable bomb with a "slow" fuse attached, used in the
case cited by Shakespeare to blow a hole in a fortification. Typically
an engineer would dig a tunnel under a wall, place his petard, and
light it, and then try to get away before the explosion. Sometimes the
wall came down, sometimes the engineer went up.

I knew that, you dingleberry. That's why I thought I was qualified to make
what I thought was a joke.

Here's one for ya:

Why did the dyslexic cross the road?

Cheers!
Rich

 

[Bobo The Chimp]

Does the radar automatically correct for the angle?

JoeBloe is ignorant ;-)
[/QUOTE]

Ignorance isn't a vice, it simply means "I do not know".

When one who is ignorant refuses to learn, then it becomes stupidity.

Unfortunately, Society has been in conflict with Nature here - stupidity
in Nature is a terminal disorder, but then Society started protecting the
stupid from the consequences of their own stupidity, and they've been
breeding like flies ever since.

And voting.

Cheers!
Rich

 

[Jim Yanik]

I would expect that a LIDAR gun uses something similar to a
direct-sequence spread spectrum pulse of LED flashes that it
correlates to back on the receiving side. That would make it rather
difficult to jam!

Anyone know for certain?

AFAIK,laser speed guns send out a 904nm laser(not LED) pulse train of about
500pps,a PW of ~30ns,and measure consecutive pulse returns to determine
distance travelled in the time between pulses,IOW,a repetitive rangefinding
then calculating speed for that time interval.Got that from a laser
industry magazine article many years ago. Today's laser guns probably have
some sort of "jam" detection,perhaps by audio like the radar runs.

 

[[email protected]]

True enough, I suppose... although it's at least a little harder than a cop
simply claiming outright you were speeding and the court taking his word
alone?

You are taking his word alone no matter what. The gun does not take a
picture or anything. It is only his word about what it read and which
car he was pointing at. They don't let you get out of your car and go
look at the radar.

 

[[email protected]]

. Today's laser guns probably have
some sort of "jam" detection,perhaps by audio like the radar runs.

The problem is "so what" the fcc does not regulate IR transmissions.