[sci.electronics] A New Approach to Radar Detection

frank@snowy.rice.edu (Franklin Tae-Sung Kang) (06/20/91)

In article <8641@awdprime.UUCP> daryl@vixen.Berkeley.EDU () writes:

>A couple of years ago, I saw an ad in Car & Driver (or one of the others)
>that offered a detector which tuned in to the repeater frequencies that
>the car radios in police cars use to forward received transmissions to
>the officer's portable walkie-talkie.

Does anyone know the frequencies of this broadcast?  It sounds like
it would be relatively easy to make.  Perhaps this is the CHiPs
detector advertised in the back of C&D all the time.

Also, does anyone truly know the range of these broadcasts?

Frank

khan@mrcnext.cso.uiuc.edu (Scott Coleman) (06/22/91)

frank@snowy.rice.edu (Franklin Tae-Sung Kang) writes:

>In article <8641@awdprime.UUCP> daryl@vixen.Berkeley.EDU () writes:

>>A couple of years ago, I saw an ad in Car & Driver (or one of the others)
>>that offered a detector which tuned in to the repeater frequencies that
>>the car radios in police cars use to forward received transmissions to
>>the officer's portable walkie-talkie.

>Does anyone know the frequencies of this broadcast?  

It varies from state to state and area to area. For a list of frequencies which
are used where you live, stop by your nearest Radio Shaft and pick up a copy 
of the Police Call book. It lists all the frequencies for a 4-state area.

>It sounds like
>it would be relatively easy to make.  

Or you could buy a portable scanner for your car. In some states this is 
illegal, however.

--
Scott Coleman                                                    tmkk@uiuc.edu
University of Illinois at Urbana-Champaign

"The military particularly liked Prodigy because the censorship came for free."
- Andrew Grove on the use of email services to send mail to troops in the gulf

mcovingt@athena.cs.uga.edu (Michael A. Covington) (06/23/91)

The trouble with trying to detect police cars by listening to their radios
is that the range is too good.  There is *always* a police car close enough
to you to give a strong signal.  In fact there are always ten or twenty,
unless you live in the Mojave Desert.

Not only that, but signal strength is not a good indicator of proximity.
Base stations put out a strong signal over a 20-mile radius. Cars put out
a signal that varies depending on exactly what is between you and it.

Finally, the police car standing still at a speed trap is not likely to be
transmitting anything.






-- 
-------------------------------------------------------
Michael A. Covington | Artificial Intelligence Programs
The University of Georgia  |  Athens, GA 30602   U.S.A.
-------------------------------------------------------

mzenier@polari.UUCP (Mark Zenier) (06/23/91)

In article <1991Jun22.175649.8327@athena.cs.uga.edu> mcovingt@athena.cs.uga.edu (Michael A. Covington) writes:
>The trouble with trying to detect police cars by listening to their radios
>is that the range is too good.  There is *always* a police car close enough
>to you to give a strong signal.  In fact there are always ten or twenty,
>unless you live in the Mojave Desert.

The police car detectors only work in cases like the California Highway
Patrol, where the car <> base signals use Low Band VHF, and in each
car the signals are repeated on a higher frequency, one that works
better for handheld radios.  There is still a lot of empty space in
California, so it's easier to carry your repeater along with you than
build a system that can pick up watt level signals on every lonely highway.

Mark Zenier  markz@ssc.uucp  mzenier@polari.uucp

khan@mrcnext.cso.uiuc.edu (Scott Coleman) (06/23/91)

mcovingt@athena.cs.uga.edu (Michael A. Covington) writes:

>The trouble with trying to detect police cars by listening to their radios
>is that the range is too good.  There is *always* a police car close enough
>to you to give a strong signal.  In fact there are always ten or twenty,
>unless you live in the Mojave Desert.

The secret is not merely to listen for the presence of a police car, but 
also the location. Whenever a cop changes status, he radios in to the
dispatcher to let them know what he's up to. If he's 10-8, it means he's
coming back on duty after a break (at the donut shop?). If you hear one
unit call for another unit to 10-25 in the 7-11, that means that the two
cars in question are going to go park in a convenience store parking lot,
each facing in the opposite direction, and chew the fat. Around here, if
you hear a unit going "code 34 at <location>" it means he's going to whip
out his radar gun and start enhancing the city coffers.

OK, so it requires more effort than using a radar detector. On the upside,
if you hear over your scanner the exact location where the cop is waiting
with his radar, isn't that BETTER than a radar detector? This technique
even works against instant-on and LIDAR (so-called "laser radar"), which
no detector on the market will protect you from.

>Finally, the police car standing still at a speed trap is not likely to be
>transmitting anything.

Au contraire. For each and every speeder he pulls over, he calls into the
dispatcher for a licence and registration check. If you're cruising around,
and you hear One-Adam-Twelve calling in a bunch of 10-27s, chances are good
he's taking pictures. Just keep listening until he relays his 10-20 to 
dispatch, and steer clear of the area.

Now, you nitpickers in the audience who are just itching to hit 'F' and
tell me how this ain't gonna work in all situations, please save your
energy. ;-) I already know there are limitations to this idea; I merely
present it as a possible component of a multi-faceted revenue enhancement
defense plan. A scanner, a radar detector, a CB, some RAM for your bra ;-),
a CHiPs Detector, a radar communicator, and a Corvette would be quite an
effective combination, don't you think?


--
Scott Coleman                                                    tmkk@uiuc.edu
University of Illinois at Urbana-Champaign

"The military particularly liked Prodigy because the censorship came for free."
- Andrew Grove on the use of email services to send mail to troops in the gulf

frank@snowy.rice.edu (Franklin Tae-Sung Kang) (06/24/91)

In article <khan.677690564@mrcnext.cso.uiuc.edu> khan@mrcnext.cso.uiuc.edu (Scott Coleman) writes:
>
>defense plan. A scanner, a radar detector, a CB, some RAM for your bra ;-),
>a CHiPs Detector, a radar communicator, and a Corvette would be quite an
>effective combination, don't you think?

Don't you mean a mouse gray Taurus SHO, Infinity Q45 or perhaps
a Lexus coupe?  You gotta maintain the visual blandness you know!
I'm working on the ultimate defense - an invisible car.  Just like
Wonder Woman's plane.  That failing, I'll contact the Romulans
to purchase a Romulan Cloaking Device. :-) :-)

Frank

dil@mace.cc.purdue.edu (Perry G Ramsey) (06/25/91)

In article <khan.677690564@mrcnext.cso.uiuc.edu> khan@mrcnext.cso.uiuc.edu (Scott Coleman) writes:
>mcovingt@athena.cs.uga.edu (Michael A. Covington) writes:
>
>The secret is not merely to listen for the presence of a police car, but 
>also the location. Whenever a cop changes status, he radios in to the

Of course, what you are talking about is using a police band receiver
in commission of a crime, something that is illegal in most states.
We who what to carry radios for legitimate purposes have no end of
trouble because of those who want to carry one in support of illegal
activities.  For more flames on this issue, see
rec.radio.amateur.misc.

Yes, I know that 55 (even 65 under most circumstances) is a stupid
speed limit.

-- 
Perry G. Ramsey         Department of Earth and Atmospheric Sciences
dil@mace.cc.purdue.edu  Purdue University, West Lafayette, IN USA
perryr@purccvm
N9LFF

tmkk@uiuc.edu (K. Khan) (06/25/91)

In article <7830@mace.cc.purdue.edu> dil@mace.cc.purdue.edu (Perry G Ramsey) writes:
>In article <khan.677690564@mrcnext.cso.uiuc.edu> khan@mrcnext.cso.uiuc.edu (Scott Coleman) writes:
>>mcovingt@athena.cs.uga.edu (Michael A. Covington) writes:
>>
>>The secret is not merely to listen for the presence of a police car, but 
>>also the location. Whenever a cop changes status, he radios in to the
>
>Of course, what you are talking about is using a police band receiver
>in commission of a crime, something that is illegal in most states.

Driving is a crime?  's news to me!!

>We who what to carry radios for legitimate purposes have no end of
>trouble because of those who want to carry one in support of illegal
>activities.  For more flames on this issue, see
>rec.radio.amateur.misc.

I remind you that my post said nothing about breaking any laws. We who
want to post to Usenet for legitimate purposes have no end of trouble
because of those who want to jump all over us because they ASSUMED we
were talking about something we weren't. ;-)

>Yes, I know that 55 (even 65 under most circumstances) is a stupid
>speed limit.

Agreed. As the report published in C&D noted, many speed limits are set
artificially low. For more flames on this topic, see rec.auto.driving.
;-) ;-) ;-)

To those of you reading along, let me reiterate that I do not condone
the use of police band receivers in the commission of any crime, which
as is pointed out above an illegal act. The discussion was merely
academic.