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Re: "Radar Scramblers"

DeWitt Harrison wrote:
> Adding the additional complication of doppler shifted return signal does
> not overcome the fundamental flaw in passive radar/lidar "jamming" devices.
> Whatever sort of reflected signal is returned from a doohickey equipped
> car will consist almost entirely of "car" and virtually nothing of "doohickey."
> Signal-to-noise-ratio. All you have to do is measure the square meters
> of the car's frontal area and compare it to the area of the passive reflecting
> device.  That ratio is signal to noise.  If we ignore the windshield area which
> may not be a good radar/lidar reflector, I think the car-to-doohickey-ratio
> would be something like 2 square meters divided by 0.0005 square meters.
> Fudge all you want, but the cop's supersensitive-califragilistic zapper will
> see all car and no doohickey. What we have here is a modern day sequel
> to "The King's New Clothes."  What is really needed is an inexpensive and
> legal radar/lidar/ovloV homing tactical nuclear missile.  Cheers,
> DeWitt Harrison    de@aztek-eng.com
> Boulder, CO
> 88 5kcstq

Wouldn't this S/N ratio assume that the jammer is only reflecting the
signal rather than contributing to the return?  I would think that we
would need to know the cop's signal strength, the % the car reflects,
and the jammers signal strength.  I have no idea how strong police radar
is so maybe this is a moot point, but simply using the cross section of
the jammer and car seems counter-intuitive.  

Maybe this has to do with active vs passive jammers.  Maybe we're
assuming that passive means it doesn't transmit, I was assuming that
passive meant off-until-needed (ie: no user input/control required). 
Isn't a non-transmitting jammer an oxymoron?  I was also assuming that
an active jammer was on all the time (like the "push button to select
speed" variety decribed earlier), and that would seem very bad to me,
talk about advertising.

Anyway, still have to worry about vascar, pacing, and lidar :-(