CD laser jammer

Archives of Posts to the NZ MX5 List back in 2003
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ross campbell

CD laser jammer

Post by ross campbell » Sun Dec 07, 2003 11:20 am

I have seen a number of vehicles with 1 or 2 CD,s in the front window
playing side out .I was told they jamb or alter radar or laser gun.Can any
one confirm this or is it a "myth".Thanks Ross.

Wayne

CD laser jammer

Post by Wayne » Sun Dec 07, 2003 11:38 am

Ross
Well I hope its not a 'myth'. Just think of all those Warehouse sales of
Nana Mouskouri CDs they can't get rid of. Have seen them on bug catchers of
big rigs - thought it was just to show off the spooky colours caused by sun
rays - but Hey - maybe I should fit a few on my work Ute.
I tell you what, I'll send some up to you to try out Ross.

Cheers Wayne


-Original Message-----
[...]

Grant
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CD laser jammer

Post by Grant » Sun Dec 07, 2003 12:12 pm

I can't see how this would work and believe it to be a myth. The disk is
purely a reflective surface with microscopic holes punched into it so that a
laser is either reflected from the surface or not when it encounters the
hole. This builds up the digital data required to reconstruct whatever has
been recorded. The CD is designed to be very reflective to infra red light.
The laser speed guns work by sending a pulse of infra red light towards the
target and measuring the time taken for the reflected pulse to return to the
gun. At a distance of say 300 metres, the area covered by the light pulse is
probably about 1 metre in diameter. Any light reflected from that 1 metre
area will be detected by the gun's receiver. The CD is only a very small
percentage of that area. The amount of reflected light is going to be quite
small, depending on the surfaces the transmitted pulse encounters, so if the
pulse hits a highly polished object that is perpindicular to the pulse, then
the return will be quite strong, so range will be good. If the object hit by
the pulse is not reflective then there will be a poor return so limited
detection range. Front reflective number plates are a very effective surface
to return the pulse from a laser gun.
If anything, I would expect the range of the laser speed gun to be enhanced
if it encounters the reflective surface of a CD in the front of a vehicle!
The cd is nothing more than a mirror with minute irregularities.
To reduce the amount of light returned to the laser gun, perhaps just having
a very dirty car would be the most effective way!
Grant.

From Michael_VanZoggel@bcait.com.au Fri Apr 27 16:51:00 2007
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It's got to be a myth. Think about light absorbant material and surface reflection / refraction. Does anyone still have 1/2 filled soft drink bottles on their lawns?

Cheers -Mike
Red 2006 NC Tiptronic
FIX A PC

EricW
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Posts: 95
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Location: Whangaparaoa

CD laser jammer

Post by EricW » Mon Dec 08, 2003 10:41 pm

Actually Grant, there is almost no scatter at all on these guns, if the beam
leaves the gun 2mm across it will still be 2mm at very long ranges (in the
order of miles), this is why they can pick you off at up to 1 km.

The whole thing works on Doppler Shift and the Laser will bounce off just
about anything, a dirty car will not help.

The CD thing is a myth, think about it, to be effective, the gun, which
transmits rapid square wave pulses that are time synched, ( a bit like a GPS
signal ) would have to hit nothing but the CD, square on, and hold that
target throughout the entire reading.

At 300 metres that means the gun has to move through no more than 1 /50,000
of a degree, relative to the disc! It would not happen, even if the car was
stationary and the gun set in concrete.

This pre-supposes that the laser did not bounce off the windscreen or the
back of the mirror or sunvisor and that the CD absorbed all of the laser
energy, and was not swinging on a string. That will not happen either.

Another digression! My little Maltese Terrier always liked the plastic
bottles on the lawn, those black ends on the early ones looked like a tiny
truck tyre and, being vertically challenged, he found it much easier to
"score a bullseye" on one of these, than on the real thing. (no bad puns
about Coke thanks)

Regards

Eric

zorruno
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CD laser jammer

Post by zorruno » Mon Dec 08, 2003 11:00 pm

I have seen a number of vehicles with 1 or 2 CD,s in the front window
playing side out .I was told they jamb or alter radar or laser gun.Can any
one confirm this or is it a "myth".Thanks Ross.
The principle of speed measurement is Doppler effect. This depends on 2
things for measurement:
a) the power of the microwave (or infrared) signal, and
b) the reflectivity of the moving target.

We can't control the power of the device (although rain, fog, trees, curves
in the road etc all lessen the distance a microwave or 'laser' (LIDAR) speed
detector can be operated effectively), but as the MX5 sits low, has no big
protruding headlights (when eyes down) and a curved smooth plastic front
surface, it is one of the least reflective vehicles on the road (not wanting
to get into a number plate debate again).

A couple of nice round reflective targets in a window would help somewhat...
maybe the rumour was started by motorway patrol?

Modern detectors with high focus beams have very little dispersion, giving
high energy at the point of the target, so just about any surface will
reflect the signal anyway.

This could actually have progressed from another vicious rumour of many
years ago, I remember someone telling me that you could make a fast spinning
disc out of a headlamp reflector and motor, and it would upset the Doppler
shift. I remember trying to do the maths years ago, and it ended up pretty
much impossible at the radar frequencies. Not to mention it would look
bloody ugly on the front of my MX5 ;)

There is only two ways to guarantee radar fine avoidance,
a) investigate http://tinylink.com/?LgBeW99vil or
b) don't drive over the speed limit ;)

cheers
zorruno
(z)

Grant
Need, more, 5-ing, time....
Need, more, 5-ing, time....
Posts: 175
Joined: Thu May 18, 2006 9:41 pm
Location: Sunny Blenheim

CD laser jammer

Post by Grant » Mon Dec 08, 2003 11:17 pm

Had a look on the internet and the sites I checked suggested the lasers work
on measuring the time delay, not Doppler shift. I assumed they used Doppler
as well, as does radar. Thinking about it, how do they detect doppler shift
with a laser? Easy with a radar system. Time delay would be an easy thing to
measure with a laser. Academic I suppose as the result is the same. They
also state that there is some spread to the beam as the extremely narrow
beams tried on earlier units made them too difficult to aim. Again seems
strange to me. I would have thought that the width of the beam wouldn't
matter. If you hit the target, then you would get a reflection.
Oh well, got a lot to learn about these things.

Grant.
Red 2006 NC Tiptronic
FIX A PC

Biff

CD laser jammer

Post by Biff » Thu Dec 11, 2003 7:49 pm

So what we need to do is find some indium-tin-oxide paint at the right
price, (red of course because we go faster) and paint the nose and
windshield and we are stealthy!
Anyone got a mate at Dulux??
Biff
ZOOM1N

Badcat
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CD laser jammer

Post by Badcat » Thu Dec 11, 2003 8:18 pm

i was told once that there is a type of paint used in microwave ovens
that is particularly good at evading speed radar/microwave.
could be bollocks though.

ken

EricW
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Posts: 95
Joined: Wed May 24, 2006 7:07 pm
Location: Whangaparaoa

CD laser jammer

Post by EricW » Thu Dec 11, 2003 10:00 pm

Sorry fellows, there is only one way of preventing these things from doing
their job and it requires little equipment or effort, just sufficient muscle
power to lift your right foot a fraction of an inch. Do that, and how they
work and how you jam them suddenly becomes redundant. The money you save can
then be used to buy CDs for their real purpose too.

Regards

Eric

Badcat
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Need, more, 5-ing, time....
Posts: 158
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CD laser jammer

Post by Badcat » Thu Dec 11, 2003 10:34 pm

thanks eric,
just needed your enlightened perspective to sort me out.
what was i thinking talking about irresponsible driving on a sports car list?
i feel so dirty.

ken


On Thursday, December 11, 2003, at 10:00 PM, Eric & Ann West wrote:

[...]

EricW
See my 5 and raise you.
See my 5 and raise you.
Posts: 95
Joined: Wed May 24, 2006 7:07 pm
Location: Whangaparaoa

CD laser jammer

Post by EricW » Sat Dec 13, 2003 12:58 pm

Sorry Ken, You missed the tongue lodged firmly in cheek.

For the record, ex traffic cops are a bit like ex smokers, and I have a very
heavy right foot. My (I have to say very, very, few) speeding tickets are
not for the offence committed at the time, more, the resolution of a
lifetime of undetected crime!

The point I make is that none of these avoidance devices actually work
against laser. But at least lasers are honest, the cop still has to stop you
and face you at the time. If he does his job well, he has to square his
conscience with the nature of the offence and the action taken. They also
give the cop a chance to discover other matters, because he actually talks
to a possibly drunk, drugged or unlicensed driver.

I am 20 years out of practice, but I will meet any wager that I could pull
up more drunks in an evening's clever patrolling, than any five officers on
the occassional "random roadblock". Nothing beats interfacing with other
people, that is a maxim the present police have long forgotten.

And when someone is, as we used to say, "Richly deserving of a pilling", the
"pilling" happens there and then, not days or weeks later. after the
offender has gone on his way, past a speed camera, continuing to offend and
presenting a danger to others, while the officer who set up the camera does
nothing. And speed cameras can only detect speed, they have never been able
to talk to drivers and never will.

That, as a former cop, is the thing I hate about cameras and the reason that
no cop, who is any good at his job, will ever convince either me or himself
that they are about safety.

Well Ken, you did get me going, didn't you.

I hope to see you guys and girls at Shakespear Park tomorrow, if Ann is well
enough, she just got out of Hospital yesterday, so if I'm there, it will be
for a few moments only

Regards

Eric

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