RE: "Radar Scramblers"

[Aleksander Mierzwa <alex@matrix.com.pl>]

DeWitt wrote:

	>It's really pretty simple. All passive, reflecting "jammers"
are a hoax and
	>fail the common sense test as well. Imagine how your vehicle
appears
	>to a radar or lidar receiver's antenna. It's analogous to your
pointing
	>a flashlight beam into the night and observing objects by the
reflected
	>light, an oncoming car for example. Your ability to see this
car depends
	>on the total amount of car-reflected light returned to your
eyeballs
	>compared to the amount from other reflective objects. These
amounts
	>depend on physical and apparent sizes (closeness) and the
reflective
	>properties of the front of the car, etc.. Now try to imagine
how it would
	>be possible for that car to become invisible to you by sticking
some
	>little reflective doohickey behind the windshield.
	>[...]
	>Passive schemes that could work are not generally practical.
The
	>entire target could be covered with non-reflective, absorbing
materials.
	>The front of the car could be shaped like a big mirror which
reflects
	>everything away from their points of origin.  Then your car
would look
	>like the stealth bomber.

Dewitt, what you've described makes perfect sense as far as we treat a
radar only as a locating device. The police radar is, however, a speed
measuring device, which uses a Doppler effect to measure the speed of
the target. Following your analogy, you would need to perform a spectral
analysis of the light reflected from the target and then measure the how
much the spectrum is "shifted" comparing to the light of your
flashlight. A typical police radar emits rather weak signal to conform
to the safety regulations on microwaves emissions and there's a constant
tendency to lower the signal strenght to make radar detectors less
effective :-) There are also high demands on police radars in terms of
reliability and accuracy, otherwise they could not have been used as a
proof. To catch up to these demands, a police radar makes a series of
measurements. It won't display the speed until the results of 10 or so
measurements are equal within 2 percent or so. A passive radar jammer
mixes the radar signal with constantly varying FM noise. It does not
makes you invicible to the radar, nor even prevents the radar from
measuring your speed, it just makes these measurements less accurate.
Actually most reputable manufacturers of the jammers don't claim that
their products will make you invicible to radar, they just say that the
jammer will prolong the time the radar needs to lock on your car,
sometimes it will make the radar not lock at all (it will keep measuring
your speed, but the results of all the measurements will not fall within
specified range), it is not guaranteed, though. That's why any jammer
should be used with a radar detector. Normally when the detector beeps,
it's already too late to brake. A jammer gives you a chance to decrease
your speed before the radar lock on your car.

Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.com.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars broke at the same time :-)