On Wed, 16 Feb 2011 15:27:25 -0600, Jim Yanik
wrote:
Jeff Liebermann wrote in
:
On Tue, 15 Feb 2011 08:32:11 -0800 (PST),
" wrote:
This type of product is advertised almost everywhere that it helps you
avoid tickets etc.
Episode 18: Beat the Radar Detector
http://mythbustersresults.com/episode18
I imagine that it must transmit a signal on the
same freq. as the radar gun at the moment it receives the police
transmission.
You have a good imagination. The illegal ones are essentially radar
jammers. That's not as easy as it sounds as getting the timing just
right so that it coincides with a radar *PULSE* is tricky. Most
handheld radars now work on several bands simultaneously, making a
universal radar jammer somewhat difficult and expensive to produce.
How are the HANDHELD radar guns multi-band?
they would have to have multiple Gunn oscillators,too.
And more than one feed horn.(antenna)
Maybe, but I've worked with horn antennas with several octave
bandwidth. It's not the horn that's bandwidth limited. It's the
waveguide feed. Figure about 0.6 octaves per standard waveguide
number:
http://www.microwaves101.com/encyclopedia/waveguidedimensions.cfm
Since only one feed need be active at a time, it's easy enough to
build a switch or just imbed the Gunn diodes or DRO (dielectric
resonant oscillator) and detector diodes in the throat of the horn,
where no waveguide is necessary. Or, just forget about the switch and
use multiple patch antennas on a PCB to feed the horn antenna:
http://www.eetimes.com/design/microwave-rf-design/4009957/Mattel-makes-a-real-radar-gun-on-the-cheap
(Note: This is an X band design, which is NOT commonly used in
current police radar guns).
Most that I've seen on police cars are pretty small units.
I'm wrong on the dual band feature. Kustom Signals advertises a "dual
K band" device (RP-1) for either K (24Ghz) or Ka (33-36Ghz) bands. I
wrongly assumed that this meant that the device was dual band. It
really means that it has two antennas, one internal and one external.
http://www.galls.com/goid/style.html?assort=general_catalog&cat=&style=LE954
http://www.kustomsignals.com/product_body2.asp?product_id=89&cat_id=8&strpagena me=fixedmount
My apologies for the wrong info and thanks for the corrections.
AFAIK,most radar guns are Doppler,and the receiver reads the strongest
signal it receives,so transmitting a signal from your "jammer" overpowers
the reflected radargun signal.That jammer signal has to be near in freq
to the gun's signal,or it will be rejected,because it would indicate a
higher speed than the gun will measure or considers reasonable.Then the
speed gun would light it's "interference" indicator.
The problem is for the jammer to figure out what frequency to jam and
then to synchronize the pulse repetition rate to that of the radar.
That's not easy when it could be arriving on X, K, Ka, and possibly Ku
bands. It doesn't take very long to get a reading and if the jammer
is listening on the wrong band or simply too slow, it will be too
late.
I have two of these radar guns, in rather poor condition:
http://www.kustomsignals.com/product_body2.asp?product_id=26&cat_id=7&strpagena me=handheld
While totally obsolete, one does function well enough to measure
speed. I must admit that I've never tested it for jamming tolerance.
Tempting to build this ummm... tester:
http://blockyourid.com/~gbpprorg/mil/wall/speed/index.html
do you have any information on or links to these multi-band radar speed
guns?
No, nor could I find any. There might be some patents but after a few
minutes of zero luck, I gave up. I recall discussing the problem
during a show with someone from Kustom Signals, who indicated that a
solution to a potential jamming problem was to frequency hop through
the available bands. At the time, only X and K bands were available,
so I assumed that this was the current technology. Apparently not.
Radar Gun FAQ:
http://www.radarguns.com/radar-guns-faq.html
Ramsey Radar Gun:
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SG7
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
#
http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS