[sci.electronics] radar countermeasures

MJSCHMEL@pucc.Princeton.EDU (Michael J. Schmelzer) (02/29/88)

Hi there everybody!
I was cruising the news and saw the subject of radar invisibility,
and it brought to mind a question that's been buggin' me for quite a
while now.
You see, I'm an ideas man. And I think I may just have a pretty
nifty countermeasure to police radar besides invisibility.
Do you think it's feasible (forget about legal for the moment because I'm
speaking, of course, hypothetically) to build a radar TRANSPONDER?
(I hear your wheels turning already)
Think about it: A little black box in your (innocuous looking) Oldsmobuick
that would, upon receiving a threat signal from smokey, rather than just
sit there and beep like an idiot telling you to slow down even though its
already too late, would send back a signal to your friendly Highway
Patrolman on his X or K or whatever that would register a perfectly
legal double nickels on the Law's satanic little radar gun's readout.
Speed with impunity! Drive those Interstates at the speed God made them for!
 
Am I talking out my ass, or do I have a beautiful (though doubtlessly
illegal) idea? I hope I've stirred up a bit of discussion here.
 
Seriously: You design the box, and we could be talking millions here.
Thanks again for your time, and LET ME KNOW WHY THIS COULD(N'T) WORK.
 
=========================================================================
comes around             Mike Schmelzer                  what goes around
=========================================================================
"Come on baby, worship me. I'm the god of fertility."
                                                 -Zodiac Mindwarp

madd@bu-cs.BU.EDU (Jim Frost) (03/01/88)

In article <4596@pucc.Princeton.EDU> MJSCHMEL@pucc.Princeton.EDU writes:
>Do you think it's feasible (forget about legal for the moment because I'm
>speaking, of course, hypothetically) to build a radar TRANSPONDER?
>(I hear your wheels turning already)
>[It] would send back a signal to your friendly Highway
>Patrolman on his X or K or whatever that would register a perfectly
>legal double nickels on the Law's satanic little radar gun's readout.
>[...] LET ME KNOW WHY THIS COULD(N'T) WORK.

I can think of a couple of reasons why building it would be
impractical and also why it probably wouldn't work.

Impractical:  Determining the proper time to send the
pseudo-reflection would be relatively difficult.

As for why it wouldn't work, your car will also send back an image.
The radar gun would get back both your image and the pseudo image that
your transponder is sending.  This would confuse the hell out of the
radar gun!

The transponder idea is a pretty good one, actually, but the idea
wouldn't be to send a "55" to the offending radar gun, but instead
send a lot of extraneous signals to cause the radar gun to become
confused ("hopelessly hosed" is probably a better term).  There are at
least two things that could be done about this kind of transponder.

The police could stop cars that appear to cause their radar guns to
screw up (I'd assume that it's not legal to transmit the signals in
the first place, and even if it is it's easy to pass a new law).

Second, a tagged radar signal would allow the gun to filter out
inappropriate signals, unless you make your transponder smart enough
to detect tagged signals and respond with the tag.  Unlikely at best,
and harder than that because it's real simple to make the gun transmit
tags that shift between transmissions (such as using a tag with a
clock value associated with it).  A transponder smart enough to handle
this would be slow in responding and cost more than the tickets would.

jim frost
madd@bu-it.bu.edu

dave@sun.soe.clarkson.edu (Dave Goldblatt) (03/01/88)

From article <4596@pucc.Princeton.EDU>, by MJSCHMEL@pucc.Princeton.EDU (Michael J. Schmelzer):
> Do you think it's feasible (forget about legal for the moment because I'm
> speaking, of course, hypothetically) to build a radar TRANSPONDER?
> (I hear your wheels turning already)
> Think about it: A little black box in your (innocuous looking) Oldsmobuick
> that would, upon receiving a threat signal from smokey, rather than just
> sit there and beep like an idiot telling you to slow down even though its
> already too late, would send back a signal to your friendly Highway
> Patrolman on his X or K or whatever that would register a perfectly
> legal double nickels on the Law's satanic little radar gun's readout.
> Speed with impunity! Drive those Interstates at the speed God made them for!

Not only feasible, but already designed.  It was published in the
Radio-Electronics (annual?  semi-annual?) special issue around this
past November.

Operation was simple: You hooked it in parallel with your radar detector;
it looked for the voltage drop caused by the detector when the alarm goes
off, and activates for 10 seconds.  Switch on the front panel for 25, 35,
or 55 mph.  Estimated cost is about $125, with the most expensive component
a Gunn diode (around $60).  Article states it is only for LAB use, since
it is (probably) highly illegal {although I'd like to saee FCC or state
regulations on such broadcasts}.

Also in there is the plan for a radar detector, which costs about $20.
It give about a mile range, according to someone I spoke to who built
it; the parts are sitting in a bad waiting for me to put 'em together. :-)

-dg-

lyndon@ncc.UUCP (Lyndon Nerenberg) (03/01/88)

In article <4596@pucc.Princeton.EDU>, MJSCHMEL@pucc.Princeton.EDU (Michael J. Schmelzer) writes:
> Think about it: A little black box in your (innocuous looking) Oldsmobuick
> that would, upon receiving a threat signal from smokey, rather than just
> sit there and beep like an idiot telling you to slow down even though its
> already too late, would send back a signal to your friendly Highway
> Patrolman on his X or K or whatever that would register a perfectly
> legal double nickels on the Law's satanic little radar gun's readout.
> Speed with impunity! Drive those Interstates at the speed God made them for!

Yes, it can be done. I built one of these with a friend several years
back using a 10GHz Gunnplexor with the short horn antenna. What we
based the idea on was that the radar gun transmitted just above the
top of the 10GHz amateur band and measured the doppler offset of the
reflected signal to determine the speed of the object. As it turns out,
the receivers in the radar guns aren't to picky about which reflection
they track (high side of pilot freq. vs. low side) - they lock on to
the strongest signal that even looks close. As a result, it was possible
for us to conduct "propogation tests" just below 10.5 GHz (the top of
tha amateur band) that were guaranteed to screw up the readout on the
radar gun. Because the Gunnplexor is rather temperature sensative, it
wasn't possible to "dial in the speed" you wanted the gun to read (although
we did build a voltage divider controlled by a set of thumbwheel switches
that tried to vary the frequency to match the expected doppler offset
for a given speed). There were also problems with calculating the fudge
factor to compensate for the (our) vehicle speed.

The end result was we spent a couple of weeks driving around town
watching a *lot* of policemen poke their heads out from behind the
cars with very *confused* expressions on their faces :-)

I also recall some companies in the U.S. selling these boxes for a few
months before the FCC (?) stopped the practice (sometime around 1978?)

--lyndon  VE6BBM (maybe not for much longer :-)
{alberta,ddsw1,utzoo}!ncc!lyndon

malcolm@spar.SPAR.SLB.COM (Malcolm Slaney) (03/01/88)

In article <20271@bu-cs.BU.EDU> madd@bu-it.bu.edu (Jim Frost) writes:
>Impractical:  Determining the proper time to send the
>pseudo-reflection would be relatively difficult.

It is very unlikely that any radar gun could be built that times the
arrival time of a reflected pulse.  Much more likely is a system based
on doppler.  See any graduate level text on communications theory (for 
example Gagliardi) or radar for more information.

Spoofing radar is very common in the defense community.  Contact your
friends at TRW or any other of the military/electronice industry for
more information.  (I can just conjecture what they do.)

								Malcolm

richard@islenet.UUCP (Richard Foulk) (03/01/88)

> >Do you think it's feasible (forget about legal for the moment because I'm
> >speaking, of course, hypothetically) to build a radar TRANSPONDER?
> >(I hear your wheels turning already)
> >[It] would send back a signal to your friendly Highway
> >Patrolman on his X or K or whatever that would register a perfectly
> >legal double nickels on the Law's satanic little radar gun's readout.
> >[...] LET ME KNOW WHY THIS COULD(N'T) WORK.
> 
> I can think of a couple of reasons why building it would be
> impractical and also why it probably wouldn't work.
> 
> Impractical:  Determining the proper time to send the
> pseudo-reflection would be relatively difficult.
> 
> As for why it wouldn't work, your car will also send back an image.
> The radar gun would get back both your image and the pseudo image that
> your transponder is sending.  This would confuse the hell out of the
> radar gun!

But it's apparently been done.  It's been a while now, but I remember
seeing ads for plans (maybe even kits) for radar spoofers in some of
the electronics hobbiest magazines.

I'm pretty sure there was even a construction article published.
Though that one billed itself as a radar calibrator -- but it did
the same thing.

If I remember correctly it was just designed to transmit a signal
that looks just like a 55mph (or whatever speed you set it to)
shift to the radar gun.  And since most of the radar guns around
currently just lock onto the strongest available signal they don't
become confused.

There was also an option to connect a radar detector to the unit
to cause it to turn on only when necessary.




-- 
Richard Foulk		...{vortex,ihnp4}!islenet!richard
Honolulu, Hawaii

max@trinity.uucp (Max Hauser) (03/01/88)

In article <20271@bu-cs.BU.EDU>, madd@bu-cs.BU.EDU (Jim Frost) writes:

> In article <4596@pucc.Princeton.EDU> MJSCHMEL@pucc.Princeton.EDU writes:
> >Do you think it's feasible (forget about legal for the moment because I'm
> >speaking, of course, hypothetically) to build a radar TRANSPONDER? ...
> >[It] would send back a signal to your friendly Highway
> >Patrolman on his X or K or whatever that would register a perfectly
> >legal double nickels on the Law's satanic little radar gun's readout.
> >[...] LET ME KNOW WHY THIS COULD(N'T) WORK.
> 
> I can think of a couple of reasons why building it would be
> impractical and also why it probably wouldn't work.

I too would be happy to say why it "could" not work if I did not already
know that it's been done. With custom microwave chips, no less. Years ago. 

Or so I understand. I myself do not know the details. 

Of course, accomplishing such a task would demand that you both knew 
exactly what you were doing and also had an element of finesse, both of
which argue fundamentally against the possibility of finding any 
authoritative guidance on the Usenet.

> As for why it wouldn't work, your car will also send back an image.
> The radar gun would get back both your image and the pseudo image that
> your transponder is sending.  This would confuse the hell out of the
> radar gun!

Forgive me, but this sounds very much like a digital person's reaction
to a straightforward analog problem.

> The transponder idea is a pretty good one, actually, but the idea
> wouldn't be to send a "55" to the offending radar gun, but instead
> send a lot of extraneous signals to cause the radar gun to become
> confused ("hopelessly hosed" is probably a better term).  

No, the idea is to send 55. Or better still, 55.4 or 59 (let's be realistic).
4596@pucc was right on target. Indeed, the way this works so well is that 
local cops expect to see confused equipment, or bad readings, but they do
not expect to see loud and clear readings of fine legal speeds. The equipment
says 59, and the equipment cost $6700, so they must be going 59, Lieutenant.

At least, this is how I understand it works.


In article <912@spar.SPAR.SLB.COM>, malcolm@spar.SPAR.SLB.COM (Malcolm Slaney)
writes:

> In article <20271@bu-cs.BU.EDU> madd@bu-it.bu.edu (Jim Frost) writes:
> >Impractical:  Determining the proper time to send the
> >pseudo-reflection would be relatively difficult.
> 
> It is very unlikely that any radar gun could be built that times the
> arrival time of a reflected pulse.  Much more likely is a system based
> on doppler.  
> 
> Spoofing radar is very common in the defense community.  Contact your
> friends at TRW or any other of the military/electronice industry for
> more information.  (I can just conjecture what they do.)

I'm not obliged to conjecture, having done it. Arrival time vs. doppler
indeed. We are mixing apples and oranges (or, as it were, range and velocity).
(Do I need to point out that even pulsed radars examine doppler shift?
Evidently). Police radars, unlike "real" radars, are concerned with velocity,
not with range: a narrow slice of the ambiguity surface. It is sufficient --
in principle, mind -- to SSB-modulate an incoming carrier with a frequency 
corresponding to the doppler shift you want on the received band, correcting 
the modulation frequency as necessary from a speedometer or wheel-tachometer
link. This could, of course, be construed as obstructing justice.

Please drive safely.

Max Hauser / max@eros.berkeley.edu / ...{!decvax}!ucbvax!eros!max

floyd@brl-smoke.ARPA (Floyd C. Wofford) (03/01/88)

In article <4596@pucc.Princeton.EDU> you write:

>Think about it: A little black box in your (innocuous looking) Oldsmobuick
>that would, upon receiving a threat signal from smokey, rather than just
>sit there and beep like an idiot telling you to slow down even though its
>already too late, would send back a signal to your friendly Highway
>Patrolman on his X or K or whatever that would register a perfectly
>legal double nickels on the Law's satanic little radar gun's readout.
>Speed with impunity! Drive those Interstates at the speed God made them for!


Good idea!  Yes it could be done.  Not cheaply, it may be prohibitive to the
general consumer.  First have only smooth curves on your vehicle, NO! sharp
edges or corners of any type!  Next cover the entire surface of the vehicle 
with an absorbing material.  Remember a curveacous type in the passenger
seat returns a signal.  Now we do not return any signal to the transmitter,
or have at least reduced its radar cross section to about the size of a
grasshopper (big radar cross section).

Now comes the fun part. We gonna fake him out.  We need to know how he
transmits.  FM-CW or some kind of pulse modulation or maybe some highly
sophisticated spread spectrum scheme.  Probably FM-CW or pulsed, 'cause they
are lots cheaper to make and use.  Nice to know his frequency too, but he
is probably using some off the shelf equipment so i probably can find out
real easily what his modulation scheme and rf is.  Oh yes, are there competing
brands to these devices, that is are the all Radio Shack or Heathkit devices
or are there different brands and models.  Do they all use the same scheme
for reading my doppler shift?  That will make my designing task a lot easier
'cause it will take a different black box to fake out an FM-CW than a pulse
system.  (I really don't know what is used).

OK so far?  Great!  Now he is going to hit me straight on (doppler shift
in radar is related to the range rate).  If i am doing my best x miles
per hour over double nickles, then my doppler shift will show that.  If I
am going y miles above, then my doppler shift will show that.  I am going
to have to vary some parameter in my transmitter in relation to the velocity
of my vehicle so THE MAN will only read double knickles, and always read
double knickles.  Remember if you are the transmitter, THE MAN is moving
with respect to you.  This is an expensive problem you wish to solve, expen-
in the sense that I am going to have to control my device with an input
from some speed indicator from the car.  This hardware will drive up the
cost of my box.

If you are in an F-16 or B1 then the cost of the countermeasure may lend
itself well to the cost of what's being protected.  For the cost of the
speeding ticket and insurance increase I am not so sure you will make
money.

What is neater, cheaper (not cheap though) and more fun is to get yerself
a TWT or equally high powered device and attach it to a real narrow beam
antenna.  Give her a great narrow modulating pulse.  You will fry his front
end or fuse his agc before he knows what hit him.  If you are caught, your
a*s will be reamed.  Consider your license plate useless for public travel,
but what the heck.

My advice at this point is to, instead, buy a Rolls Royce and a chauffeur,
install a cd player, vcr and bar in the back, crank up yer Megadeth, Metallica
or Blood Sucking Pigs cds, put on yer Leave it to Beaver or Rocky & Bullwinkle
tapes, and mellow out with a quart of Jack Daniels.  Your chauffeur will then
be the only one who worries about the speed limit. 

Any government frowns on the use of countermeasures against its law enforcing
agencies.  What you propose is highly illegal.  Governments enjoy monopolies
despite any political rhetoric.  Try printing twenty dollar bills as an
entrepreneurial venture to test my assertion.  They also assert monopolistic
divine providence to use electronic means to detect scofflaws, and legislation
to protect themselves from not being allowed to use their precious equipment.
Jammers, detectors, decoys, masking agents and deceptive devices are probably
illegal in any states.

You do have a good idea.  It is one that has been worked on in the counter-
measure field.  It is both difficult and expensive, both of which are good
reasons to explore the field.  You might make more money if you can come up
with an absorbing paint.


Floyd Wofford
floyd@brl.arpa

scw@CS.UCLA.EDU (03/01/88)

What you really need is not a Xponder (mode C?) but a Jammer,
Police Radar is really a CW Doppler radar, what you need to do is
detect an incoming signal (on the band in question) and transmit a
signal that varies its frequency so that the recieved signal appears to
be from a target whose speed is varying from -200 to +200 MPH over a period
of about 1 second, then listen for ~.1 sec to see if he's still transmitting.
This will keep the police radar from locking onto your (weaker) reflected
signal. His gun will needs a fairly stable signal to lock onto. The nice
thing about this is that unless you regulary drive in the 100+ MPH range
his radar will never get any reasonable speed for your car (from either
direction).
<scw>

Stephen C. Woods; UCLA SEASNET; 2567 BH;LA CA 90024; (213)-825-8614
UUCP: ...!{{inhp4,ucbvax,{hao!cepu}}!ucla-cs,ibmsupt!ollie}!scw 
ARPA:scw@SEAS.UCLA.EDU  <-note change from cs.ucla.edu

klavan@aecom2.AECOM.YU.EDU (Yossi Klavan) (03/02/88)

In article <4596@pucc.Princeton.EDU>, MJSCHMEL@pucc.Princeton.EDU (Michael J. Schmelzer) writes:
> Think about it: A little black box in your (innocuous looking) Oldsmobuick
> that would, upon receiving a threat signal from smokey, rather than just
> sit there and beep like an idiot telling you to slow down even though its
> already too late, would send back a signal to your friendly Highway
> Patrolman on his X or K or whatever that would register a perfectly
> legal double nickels on the Law's satanic little radar gun's readout.
> Speed with impunity! Drive those Interstates at the speed God made them for!


Sorry to dash your hopes, but a friend of mine did something like the
transponder you described.  It sent back a legal 54 MPH every time his
car was being radar watched.  My friend did more than taht, he had a few
variable settings, ie. 02 MPH, 189 MPH, etc. He would love going down a
certain street in my town where the radar happy patrolmen hang out, and
give them a taste of their own medicine.

My friend never did anything for money, just for gags. I'm also sure that
he didnt think of the idea...

Yossi Klavan
Yeshiva College
Torah U'Madah University (Home of the Mall & the Wall)

UUCP ...!aecom!aecom2!klavan

reid@decwrl.dec.com (Brian Reid) (03/02/88)

In the 1960's I worked as a programmer in a university laboratory whose
focus was on low-noise electronics and interplanetary microwave communication.
(moon-to-earth telemetry, for example).  Our lab had quite a number of
hot-shot microwave people in it.

One of the guys built what I consider to be the ultimate radar jammer. It was
passive. His car had a plastic grille. Behind the grille he put a 12-inch
audio loudspeaker. On the surface of this loudspeaker he had glued several
thousand copper dipoles, sprinkled at random, that were carefully cut to be
half-wave (or was it quarter-wave; I can't remember) at police radar
frequencies. The dipoles were individually dipped in varnish so that when the
crossed each other as they were sprinkled on the speaker grille, they would
not make electrical contact.

This speaker was connected to an audio oscillator in his car, whose frequency
he could control with a knob on the dashboard. Because the copper dipoles
were the correct length, they reflected (absorbed and reradiated, probably)
vastly more of the radar signal than the body of the car. By carefully
choosing the waveform that went into the loudspeaker, he could set the
frequency of the doppler-shifted signal received by the police radar.

One of my most joyous memories of my college years was the Sunday morning
that I helped him calibrate the thing with a radar gun borrowed from the
university police (some friend of a friend was a policeman who was amused by
the concept, and he let us use their radar for the morning). We were able to
pretty much dial the speed that the cops would see, anywhere from the true
speed of the car up to about 200 mph. It didn't seem to work to set a speed
lower than the car was going, but if the car was traveling 60mph and the dial
was set right, the radar readout would show 200mph, which was so obviously
false that (in theory, anyhow) the cop would have no data.

This guy drove like Buck Rogers, and during the time I knew him he never got
a radar speeding ticket, so I guess it worked.

dmt@ptsfa.UUCP (Dave Turner) (03/02/88)

In article <4596@pucc.Princeton.EDU> MJSCHMEL@pucc.Princeton.EDU writes:
>speaking, of course, hypothetically) to build a radar TRANSPONDER?


I had the same idea 25 years ago.

Most speed radars measure the doppler shift of the received signal.
For a given transmitted signal one can calculate the return frequency to give
any desired doppler shift (desired indicated mph). If the transmitted signal
always had a constant known frequency all that is necessary is to generate
a fixed frequency that will provide the desired readout.

A more elaborate transponder would subtract the speed of the moving car
from its received frequency to compensate for the doppler shift of the
moving car before transmitting a suitable higher frequency to give a legal
speed on the police radar.

To combat hand-held radar that are turned on and off to try to defeat
radar detectors the transponder should not transmit except when a signal
is received.

The police radar guns that I've read about will lock onto the strongest signal
so the transponder signal should dominate the radar gun readout.

I never built such a device but Radio Electronics magazine for August, 1986
(p. 39) has a construction article that will work. They call it a
"Radar Speed-Gun Calibrator" for X and K bands. Illegal? You bet.


The same idea should work for laser speed detectors that use doppler shift
but the implementation would probably be more difficult.
But if sufficient power is available just blast the speed detector, the police
squad car, etc. It would also be useful to blast cars that run red lights,
cut you off without signaling, jaywalking pedestrians, etc. :-)


-- 
Dave Turner	415/542-1299	{ihnp4,lll-crg,qantel,pyramid}!ptsfa!dmt

bill@videovax.Tek.COM (William K. McFadden) (03/02/88)

In article <4596@pucc.Princeton.EDU> MJSCHMEL@pucc.Princeton.EDU writes:
>Think about it: A little black box in your (innocuous looking) Oldsmobuick
>that would, upon receiving a threat signal from smokey, rather than just
>sit there and beep like an idiot telling you to slow down even though its
>already too late, would send back a signal to your friendly Highway
>Patrolman on his X or K or whatever that would register a perfectly
>legal double nickels on the Law's satanic little radar gun's readout.

Actually I think this has already been done.  There is (was?) a company here
in Beaverton that sold plans for a "Police Radar Jammer" that could be set
to give a fixed speed reading or a percentage of your actual speed.  A friend
of a friend once sent for the plans and showed them to me.  At the time
(~1984), the plans looked reasonable to me (i.e., it looked like this thing
would work).  I don't remember much of the theory, but the idea behind it was
to transmit a signal of such power that it was much stronger than the
reflection off your car and would thus capture the radar gun's receiver.  Once
you got to this point, you could modulate your transmission in such a way as
to cause any reading you wanted to be displayed on the radar gun.  I don't
know if this company is still in business, but if anyone is interested I could
look up their address.  BTW, I don't think the guy who ordered the plans ever
got around to actually building the thing.
-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077
UUCP: ...{hplabs,uw-beaver,decvax}!tektronix!videovax!bill
GTE: (503) 627-6920         "How can I prove I am not crazy to people who are?"

max@trinity.uucp (Max Hauser) (03/02/88)

In article <305@bacchus.DEC.COM> reid@decwrl.UUCP (Brian Reid) writes:
>
>One of the guys built what I consider to be the ultimate radar jammer. ...
>His car had a plastic grille. Behind the grille he put a 12-inch
>audio loudspeaker. On the surface of this loudspeaker he had glued several
>thousand copper dipoles, sprinkled at random, that were carefully cut to be
>half-wave (or was it quarter-wave; I can't remember) at police radar
>frequencies. ...

Scattering needles! Marvelous. Shades of Project West Ford (sp?) of the
late 1950s. (Surely even on the Usenet are some who have heard of 
West Ford -- old farts, no doubt...)

It is the most elegant approach I've seen yet to this (increasingly classic)
radar-jamming "problem."

M. Hauser

wtm@neoucom.UUCP (Bill Mayhew) (03/02/88)

Radio Electronics has a history of publishing quasi-legal
do-it-yourself articles, such as: a TV descrabler, Radar Gun
spoofer,...  They get away with it on the basis that the articles
are for information only and should not be used to construct
illegal devices.  Chuckle.

Two years ago, R-E published a DIY article to build a radar gun
spoofer.  They published the article supposedly for the purposes of
calibrating your own radar gun that you use to measure the speed of
your kid's softball/baseball/..? pitches.  Right!  (I guess they
never heard of something simple like a tuning fork.)

The basic operation of the circuit was a Gunnplexer that was
modulated by an audio carrier that corresponds to the doppler shift
for a given MPH.  I don't have my phyiscs book here, and I'm too
lazy to calculate it; i think it works out to 3.2 Hz per MPH.  You
simply set the modulator to the speed you want to the radar gun to
read.

I thought it was a nice touch that their sports radar gun tuner
included a relay the you could attach to the LED on a radar
detector so that you wouldn't run down the battery on the radar gun
tuner.  The idea is that the gunnplexer would only come on when
illuminated by a radar source.  Right.

If you are determined to build an illegal device like that, go to
your pulbic library and look up the specific issure of R-E in the
Reader's Guide to Periodical Literature.  I'm pretty sure it was
published within the last two years.

--Bill

jac@penguin.UUCP (James Carter) (03/02/88)

In article <4596@pucc.Princeton.EDU>, MJSCHMEL@pucc.Princeton.EDU (Michael J. Schmelzer) writes:
> Do you think it's feasible (forget about legal for the moment because I'm
> speaking, of course, hypothetically) to build a radar TRANSPONDER?

When I was in the AF, our ECM class played with the idea of converting some
surplus jamming equipment for automotive use. It is do-able, it is ILLEGAL,
and it might be fun.

> already too late, would send back a signal to your friendly Highway
> Patrolman on his X or K or whatever that would register a perfectly
> legal double nickels on the Law's satanic little radar gun's readout.

Why just 55? Our concept was to feed enough noise toward the gun as to
render it completely useless. Or we thought we could have fun by sweeping
a noise signal (very rapidly) across his bandwidth. Either way, the speedgun
would require minor :-) adjustments afterward.

Disclaimer: THIS IS NOT A GOOD IDEA...IT IS NOT RECOMMENDED BY ME...

-- 
==========================================================================
	Fast Enough  - Never Is!	| James A. (JC) Carter
	Big Enough   - Never Is!	| Penguin Business Systems, Inc.
	Cheap Enough - Never Is!	| ..!rutgers!pbox!romed!penguin!jac

davea@hpscdd.HP.COM (Dave Angelini) (03/02/88)

Here is agood one,

My brother is in an f-18 squadron down in Lemoore Ca. and one of the planes he 
flies in gave some good ideas to a maintenance person (non-military) This guy
has a Vet that had a very unique air dam on the hood. The whole electronics
package is hid so well that a casual inspection would never reveal it's
presense. 

There is not much finess in his system but he makes up for that with large and
very "quick" power transmission. I can see this could cause a big bill to
taxpayers. 

                                            Dave
                   (what is the missile solution for a CHP patrol car? )

todd@uop.edu (Dr. Nethack) (03/03/88)

In article <4596@pucc.Princeton.EDU>, MJSCHMEL@pucc.Princeton.EDU (Michael J. Schmelzer) writes:
> Hi there everybody!
> Think about it: A little black box in your (innocuous looking) Oldsmobuick
> that would, upon receiving a threat signal from smokey, rather than just
> sit there and beep like an idiot telling you to slow down even though its
> already too late, would send back a signal to your friendly Highway
> Patrolman on his X or K or whatever that would register a perfectly
> legal double nickels on the Law's satanic little radar gun's readout.

This has already been done, the main problem is that the police guns
tend to read the highest speed (as they measure the crowd, or try to).

If you tell it you are travelling at 55, it will pick out the higher
speed.  The solution has been to inject a higher than obvious speed..

say 110-140, the machine defaults to that, and the fuzz can see you are
not going that fast, so he takes his gun in for repair.

There were some other comments about this earlier on, anyone remember the
rest?

rlf@mtgzy.UUCP (XMRN10000[saf]-r.l.fletcher) (03/03/88)

> Think about it: A little black box in your (innocuous looking) Oldsmobuick
> that would, upon receiving a threat signal from smokey, rather than just
> sit there and beep like an idiot telling you to slow down even though its
> already too late, would send back a signal to your friendly Highway
> Patrolman on his X or K or whatever that would register a perfectly
> legal double nickels on the Law's satanic little radar gun's readout.
> Speed with impunity! Drive those Interstates at the speed God made them for!
>  
> Am I talking out my ass, or do I have a beautiful (though doubtlessly
> illegal) idea? I hope I've stirred up a bit of discussion here.
>  
> Seriously: You design the box, and we could be talking millions here.
> Thanks again for your time, and LET ME KNOW WHY THIS COULD(N'T) WORK.

I think it will work but...

A friend of mine sent me plans for a jammer (~4 years ago) that had
two modes of operation:

	1. Dial in the speed you want the cop to see on his end.

	2. Dial in a percentage of what you want removed from your true
	   speed.

I never built it nor do I know anyone who did but its drawbacks were
obvious. You are transmitting (constantly) on the radar bands (illegal), and
the parts for it included a radar gun type transmitting antenna (hard to find)
and a radar detector type receiving antenna. Since you are transmitting
whenever the unit is in operation it would be an easy task for the FCC
to triangulate your position and take you and your gadget to a place
where rf signals would be about the only thing that gets in or out :-).

john@anasaz.UUCP (John Moore) (03/04/88)

In article <469@sun.soe.clarkson.edu> dave@sun.soe.clarkson.edu (Dave Goldblatt) writes:
>a Gunn diode (around $60).  Article states it is only for LAB use, since
>it is (probably) highly illegal {although I'd like to saee FCC or state
>regulations on such broadcasts}.
(1) Obstruction of justice - they can get you for messing with their speed
     trap
(2) Communications act of 1934 makes it a federal crime to Jam signals
(3) FCC rules make it illegal to transmit without
     identification (except in specifically allowed cases).









-- 
John Moore (NJ7E)   hao!noao!mcdsun!nud!anasaz!john
(602) 870-3330 (day or evening)
The opinions expressed here are obviously not mine, so they must be
someone else's.

guest@hyper.UUCP (guest) (03/04/88)

In article <1123@pasteur.Berkeley.Edu>, max@trinity.uucp (Max Hauser) writes:
> In article <20271@bu-cs.BU.EDU>, madd@bu-cs.BU.EDU (Jim Frost) writes:
> 
> > In article <4596@pucc.Princeton.EDU> MJSCHMEL@pucc.Princeton.EDU writes:
> > >Do you think it's feasible (forget about legal for the moment because I'm
> > >speaking, of course, hypothetically) to build a radar TRANSPONDER? ...
> > >[It] would send back a signal to your friendly Highway
> > >Patrolman on his X or K or whatever that would register a perfectly
> > >legal double nickels on the Law's satanic little radar gun's readout.
> > >[...] LET ME KNOW WHY THIS COULD(N'T) WORK.
> > 

Radio-Electronics (August 1986 issue) gives construction details for a
'radar-calibrator' which does exactly what you want.

Police radar works on the principle that the doppler shifted return
signal beats with the internal reference signal, the beat frequency is
proportional to the speed of the car.  Simply AM modulate an X or
K band rf signal with the appropriate frequency (in the audio or sub-
audio range, depends on desired speed and radar freq) and it will
over power the beat mechanism in the radar, causing it to lock on
to your 'programmed' speed.

John Logajan umn-cs!hyper!ns!logajan
Network Systems Corp
7600 Boone Ave
Brooklyn Park, MN  55428

joel@mit-amt.MEDIA.MIT.EDU (joel s. kollin) (03/04/88)

A few years ago someone was selling plans for a radar device for 
about $15 or so.  A co-worker who did ECM in the air force bought them
and said they very well might work, but he wasn't going to build it
because the severe legal penalties...

joel

rsilvers@hawk.ulowell.edu (Amigas Dominate) (03/04/88)

     I have seen police radar guns that light up "JAM" on the display if it
recieves a signal other than it's own.  I suppose that most police
departments cannot afford this latest technology though.

						--Rob.




|--------------------------------------------------------------------------|
|Robert Silvers.           (617) 452-8814 Rm. 322                          |
|University of Lowell.            ______                                   |
|--------------------------------------------------------------------------|

commgrp@silver.bacs.indiana.edu (BACS Data Communications Group) (03/04/88)

Plans and semi-kits for speed-radar jammers are commercially avail-
able, ostensibly for use by racing drivers to keep competitors from 
timing them during trials.  Yeah, right! :-)

_Car and Driver_ magazine published a survey of radar jammers a few 
years ago (sorry, can't cite specific reference), in which they 
concluded that the jammers are worthless.  The most effective jammer 
was able to decrease radar acquisition range by 25%.

I knew a guy who worked in a Nike Ajax missle radar van while he was 
in the army in the '50s.  He said, "The cops used to set up a radar 
trap on the hill near our base... We'd point the antenna at them and 
burn out the diode in their receiver.  After a while, they'd figure 
out that it wasn't working and leave... Once on Armed Forces Day, a 
press photographer with his pockets full of flashbulbs walked across 
the field... We turned the antenna on him and they all went off!"

Good war stories, but this is whole discussion barks up the wrong 
tree.  Cops, being few in number, are least among the biological 
hazards of the highway.  The geeks who think they own the road because 
they have radar detectors ("No cops = no speed limit") are a greater 
threat.  ECMing their "fuzzbusters" is a lot easier than jamming cop 
radar and, until someone invents the orgasmotron, is the most fun you 
can have with electronics!  All you need is the microwave source from 
a junked radar burglar-alarm or door opener ($10 at a hamfest).

--

Capt. Blackout

sj1f+@andrew.cmu.edu (Steven Kent Jensen) (03/04/88)

I have seen this product not on the market, labeled (of course) not for use 
against police radar.  It would register on the radar gun either a preset 
speed of a percentage of your real speed.

				Steven Jensen

dbraun@cadev4.intel.com (Doug Braun ~) (03/05/88)

Someone mentioned the fact that someone using a radar gun with an
audio output would become aware of jammers.  This definitely seems
true, and it would make me very reluctant to try a jammer.  If
you had a jammer with a constant pitch AM output, it would sound
a LOT different than the normal Doppler tone.  The Fuzz would
also wonder why you were doing 54 ever after he pulled you over :-)
Even if the pitch of your AM signal was connected to the speedometer
(to give a constant fraction of your true speed), the recieved signal
would not have the noise and jitter that a real signal would have.
I'm SURE you cauld easily detect this by ear.

There is a problem with the jammer-hooked-up-to-the-detector-output
idea.  As soon as the radar detector trips, and turns of the jammer,
the output of the jammer will drive the detector crazy, and the whole thing
will lock up.  I think you wiuld need a jammer that shuts off for a
few microseconds every few milliseconds, and listens to see if
the police radar signal is still there.


Doug Braun				Intel Corp CAD
					408 496-5939

 / decwrl \
 | hplabs |
-| oliveb |- !intelca!mipos3!cadev4!dbraun
 | amd    |
 \ qantel /

matthew@ucscb.UCSC.EDU (73550000) (03/05/88)

In article <1101@silver.bacs.indiana.edu> commgrp@silver.bacs.indiana.edu (BACS Data Communications Group) writes:
>         ECMing their "fuzzbusters" is a lot easier than jamming cop 
>radar and, until someone invents the orgasmotron, is the most fun you 
>can have with electronics!  All you need is the microwave source from 
>a junked radar burglar-alarm or door opener ($10 at a hamfest).
>

Or your own radar gun (moving doppler type)
It's a GREAT toy to mount on your car,... keeps the people
around you slowed down... and you get to see how fast they're going
if they don't have a fuzzbuster.

In my experience a good X band radar unit can get an accurate
speed fix EVEN WHILE MOVING  L O N G before the target's detector
goes off.  What good are they, anyway?

(p.s.: I have the radar unit thanks to a sci.electronics posting)

Matthew Kaufman (KA6SQG)
matthew@ucsck.ucsc.edu     ...!ucbvax!ucscc!ucsck!matthew

sampson@killer.UUCP (Steve Sampson) (03/06/88)

In article <2203@saturn.ucsc.edu>, matthew@ucscb.UCSC.EDU (73550000) writes:
> Or your own radar gun (moving doppler type)
> It's a GREAT toy to mount on your car,... keeps the people
> around you slowed down... and you get to see how fast they're going
> if they don't have a fuzzbuster.

Great, idiots setting off our alarms now.

> In my experience a good X band radar unit can get an accurate
> speed fix EVEN WHILE MOVING  L O N G before the target's detector
> goes off.  What good are they, anyway?

This is generally not true.  The detectors have an excellent MDS and can
sound an alarm with a signal level that the radar gun would otherwise
ignore.  What kind of testing did you do?  I don't believe it! Prove it,
etc.  Radar detectors are good for checking your speed against the limit
when radar is detected.  This saves you money.  What kind of detector did
you use in your test?  I want to stay away from it...

> Matthew Kaufman (KA6SQG)
> matthew@ucsck.ucsc.edu     ...!ucbvax!ucscc!ucsck!matthew

lharris@gpu.utcs.toronto.edu (Leonard Harris) (03/08/88)

Just wondering - what would these radar jammers/emitters do to home
security systems - or banks?  My car radar detector goes off whenever I
pass by a bank due to their security system.  Where will all this lead...

henry@utzoo.uucp (Henry Spencer) (03/08/88)

> > In my experience a good X band radar unit can get an accurate
> > speed fix EVEN WHILE MOVING  L O N G before the target's detector
> > goes off...
> 
> This is generally not true...

Radar signal return follows an inverse-fourth-power law, inverse-square
outbound and again inbound, assuming diffuse reflection.  Radar detection
is only inverse-square, since the signal doesn't make a round trip.  Other
things being equal (detection technology, size of antenna, etc.), this
means that a radar signal can always be detected from well beyond the
effective range of the radar itself.  Of course, other things aren't always
equal, and if the radar isn't in steady use, a range advantage may not mean
a time advantage.
-- 
Those who do not understand Unix are |  Henry Spencer @ U of Toronto Zoology
condemned to reinvent it, poorly.    | {allegra,ihnp4,decvax,utai}!utzoo!henry

todd@uop.edu (Dr. Nethack) (03/09/88)

In article <1988Mar7.161433.21780@gpu.utcs.toronto.edu>, lharris@gpu.utcs.toronto.edu (Leonard Harris) writes:

> Just wondering - what would these radar jammers/emitters do to home
> security systems - or banks?  My car radar detector goes off whenever I
> pass by a bank due to their security system.  Where will all this lead...

That is most likely due to the implementation of microwave motion
detectors that can be placed in a rather sneaky fashion, since they
will shoot through solid objects. 

One company kept getting calls to a warehouse to fix false alarms, until
it was discovered that the unit was picking up passing trains outside.

They rehung the unit.

I like infrared myself, microwave is good if you want to cover several
stories or areas regardless of walls in the way.

Sonics tend to create falses due to movement of fan blades, phones that
ring in harmonic range of the detector, and cob-web spiders building
nests in the recievers.

I usually think about how I would break in, and then spend my time
laying traps and misinformation for the would be theives.

In this way you force them to do something that causes their demise.

--such philosophy is another story   ;-)


-----------------------------------------------------------------------
+ uop!todd@uunet.uu.net                                               + 
+                 cogent!uop!todd@lll-winken.arpa                     + 
+                                 {backbone}!ucbvax!ucdavis!uop!todd  + 
-----------------------------------------------------------------------

jack@cs.hw.ac.uk (Jack Campin) (03/10/88)

Expires:

Sender:

Followup-To:



[ignore the above email address and use my signature]


commgrp@silver.bacs.indiana.edu (BACS Data Communications Group) writes:
>  ECMing their "fuzzbusters" is a lot easier than jamming cop 
>radar and, until someone invents the orgasmotron, is the most fun you 
>can have with electronics!
>Capt. Blackout

I have actually seen an orgasmotron. When I was at school we got a visit from
a scientist at the local animal research lab, where they had developed a gizmo
for making rams ejaculate - it used low-voltage square waves applied to the
prostate gland. It looked like a one of those piezoelectric things for lighting
gas stoves, only the wand was 18 inches long. It seems like an obvious thing
for the sex toy industry to produce, but as far as I know they haven't.

Anyone know the voltage and frequency?

-- 
ARPA: jack%cs.glasgow.ac.uk@nss.cs.ucl.ac.uk
JANET:jack@uk.ac.glasgow.cs       USENET: ...mcvax!ukc!cs.glasgow.ac.uk!jack
Mail: Jack Campin, Computing Science Department, University of Glasgow,
      17 Lilybank Gardens, Glasgow G12 8QQ, Scotland (041 339 8855 x 6045)

wolfgang@mgm.mit.edu (Wolfgang Rupprecht) (03/10/88)

In article <1988Mar7.233054.235@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>Radar signal return follows an inverse-fourth-power law, inverse-square
>outbound and again inbound, assuming diffuse reflection.  Radar detection
>is only inverse-square, since the signal doesn't make a round trip.  Other
>things being equal (detection technology, size of antenna, etc.), this
>means that a radar signal can always be detected from well beyond the
>effective range of the radar itself.  Of course, other things aren't always
>equal, and if the radar isn't in steady use, a range advantage may not mean
>a time advantage.

This observation of inverse-fourth power for diffuse reflection vs.
distance is brilliant. (I wish I'd thought of that!)

I don't think that this is the typical limitation a police radar is
operating under, though. For the most part, cops have gotten more
clever and aren't "shining" their radars down long stretches of
straight roads anymore. This gives people with radar detectors too
much warning. (And leads to the situation that Henry describes, where
detection will always win.) Many of the radar traps now seem to
illuminate the road at an oblique angle around rocks or bridges, where
the difference in longitudinal distance for being in the radar "shade"
to being in the full flux is only a few tens of feet. This doesn't
give the driver much reaction time. One saving grace in a situation
like this is that other cars ahead of you, will act as radar mirrors,
often reflecting the signal "around the corner" for you. Nothing like 
keeping a few "passive scouts" in front of you!



Wolfgang Rupprecht	ARPA:  wolfgang@mgm.mit.edu (IP 18.82.0.114)
326 Commonwealth Ave.	UUCP:  mit-eddie!mgm.mit.edu!wolfgang
Boston, Ma. 02115	TEL:   (617) 267-4365

il01+@andrew.cmu.edu (Ihor Andrew Lys) (03/11/88)

It seems odd that no one has come up with this idea yet.  

A small fan blade, turning in the wind, in front of your car
would cause havoc on a radar gun.  The approach works for only one 
band, but so what, get 3.

The absolute best way to solve the problem is to just blast a few hundred 
watts
for a microsecond or two out in front, and turn that Gunn diode into a
bussbar. (or saturate the recieving amps).

By zapping it for a short time, the gun would not have time to react
(display JAM) and you would solve everybody else's problems that day too.

Its probably dangerous, illegal, immoral, fattening ..... but who cares?


il01@andrew.cmu.edu  If its not fun - don't bother.

davef@brspyr1.BRS.Com (Dave Fiske) (03/17/88)

In article <7386@brl-smoke.ARPA>, floyd@brl-smoke.ARPA (Floyd C. Wofford) writes:
> In article <4596@pucc.Princeton.EDU> you write:
> 
> >Think about it: A little black box in your (innocuous looking) Oldsmobuick
> >that would, upon receiving a threat signal from smokey, rather than just
> >sit there and beep like an idiot telling you to slow down even though its
> >already too late, would send back a signal to your friendly Highway
> >Patrolman on his X or K or whatever that would register a perfectly
> >legal double nickels on the Law's satanic little radar gun's readout.
> >Speed with impunity! Drive those Interstates at the speed God made them for!
> 
> 
> Good idea!  Yes it could be done.  Not cheaply, it may be prohibitive to the
> general consumer.  First have only smooth curves on your vehicle, NO! sharp

On seeing this, I dug out an old photocopy I made about 4 years ago
from the "Marketplace" section of Computers and Electronics magazine
(R.I.P).  It has a small picture of a box with some LEDs and buttons
and reads:

"Worlds Most Remarkable Radar Jammer!

Causes speed radar guns and devices to read out your choice of either a
percentage of your true speed when in automatic mode (example: Your
speed; 76 mph, auto mode set for 75%, speed displayed--57 mph), or the
speed that you dial in when in manual mode.  Transmits only in the
presence of speed radar, or by manual override. Operates on both X and
K bands. WARNING: The device described in this literature is not legal
for use against police radar, and is not FCC approved."


You were supposed to send $14.95 to Phillips Instrument Design Co. in
Portland, Oregon for the plans.  Whether it would really work, I can't
tell.

I love that disclaimer though!  I guess the only reason to get one
would be for ... home use.
-- 
     "LASER BEAM SETS BRAIN               Dave Fiske  (davef@brspyr1)
      SURGERY PATIENT ABLAZE"             BRS Information Technologies
                                          Latham, NY
 Headline from Weekly World News          UUCP:brspyr1!davef 

madd@bu-cs.BU.EDU (Jim Frost) (03/17/88)

In article <3615@bloom-beacon.MIT.EDU> wolfgang@mgm.mit.edu (Wolfgang Rupprecht) writes:
>I don't think that this is the typical limitation a police radar is
>operating under, though. For the most part, cops have gotten more
>clever and aren't "shining" their radars down long stretches of
>straight roads anymore. [...]
> Many of the radar traps now seem to
>illuminate the road at an oblique angle around rocks or bridges, where
>the difference in longitudinal distance for being in the radar "shade"
>to being in the full flux is only a few tens of feet. This doesn't
>give the driver much reaction time.

Worse, many will hide their cars completely and shine towards the back
of the car, or to "shotgun" you, which means snap on the gun if they
think you're speeding.  Either way, you can't detect it in any
reasonable amount of time, and in the case of shotgunning you haven't
a chance.  One thing that helps is that they're behind you when it
happens; an all-out run has a good chance of working, since you're
already doing some 60mph or more better than the cruiser.  I don't
personally condone this sort of thing, but if they're going to take
your license away anyway, what's the difference? :-)

jim frost
madd@bu-it.bu.edu

robertl@bucsb.UUCP (Robert La Ferla) (03/29/88)

Jim,

	There's one way around shotgunning that I know of.  Follow another
car.  The cop will 'shotgun' the car in front of you and your radar detector
will pick up the beam that bounces off that car.  neat, ay?  oh yeah - i got
another speeding ticket last fri nite!  i forgot to turn on my detector!

-rob