Path: utzoo!attcan!uunet!olivea!mintaka!snorkelwacker.mit.edu!usc!zaphod.mps.ohio-state.edu!ub!dsinc!netnews.upenn.edu!eniac.seas.upenn.edu!depolo From: depolo@eniac.seas.upenn.edu (Jeff DePolo) Newsgroups: sci.electronics Subject: Re: POLICE hand-held RADAR units Message-ID: <37593@netnews.upenn.edu> Date: 15 Feb 91 01:19:07 GMT References: <1991Feb12.035201.16098@nntp-server.caltech.edu> <2470014@hp-vcd.HP.COM> <1991Feb14.015812.14576@nntp-server.caltech.edu> <3498@casbah.acns.nwu.edu> Sender: news@netnews.upenn.edu Reply-To: depolo@eniac.seas.upenn.edu (Jeff DePolo) Organization: University of Pennsylvania Lines: 75 In article <3498@casbah.acns.nwu.edu> squishy@casbah.acns.nwu.edu (Shishin Yamada) writes: >As the recent holder of a new speeding ticket, also from speed radar. I got >clocked at 69 in a 40mph zone on Lake Shore Drive in Chicago at 1 in the >morning. There was NOBODY else on the freeway. I wascurious as to the >frequencies used for X & K band radar. X: 10.525 GHz K: 24.150 GHz >Are these government frequencies? No. They are classified as "radiolocation". They are also shared allocations. For example, some motion-sensors used for opening the doors at your local supermarket are on 10.525 GHz. 24.150 is in the middle of the amateur radio 24 GHz band. >Does FCC Part 15a apply to a radar signal >generator (ie jammer)? No. Intentional jamming or interfering with another radio (radar gun), whether the device is a part 15 device or not, is illegal. Radar guns are part 15 devices, but that doesn't mean that you can maliciously jam them. It just means that other devices being operated for a valid reason can interfere with the part 15 device legally. >I know that often cheap radar detectors will set of >one another becuase they usually have a local oscillator that I think >connects to an AM Super Heterodyne Receiver. Not quite. The echo signal is mixed with the original signal in a nonlinear device (a detector diode or the Gunn diode itself) and the difference frequency is fed to a counter or PLL (or, in moving radar, into 2 counters or PLL's). >My pink cloud project would be >to build a signal generator pegged to a radar detector to turn on when >radar signals are detected. However, I do not know the precise effects it >would have on Doppler radar (I would expect superposition of the signals), >but I do not know what the radar gun's filtering systems are. This is how most radar jammers are supposed to work. You pulse a X band/K band signal (doesn't have to be right on his frequency) to cause a perceived doppler shift in the radar gun. The speed at which you pulse is the frequency you want to be displayed on smokey's gun. >If this is illegal, how good does a radar gun do. Getting a speeding >ticket, just makes me want to buy one even more now. However, I do not know >wht good it would do, depending on how fast you can *brake*. Braking VERY hard will often cause no readings. Most radar guns have some sort of a verification system. It will re-sample the counter's result a few times (like 5 or 10 or whatever). If all of the numbers come up the same, it displays the reading. If not, it leaves the display blank. Hence, if you're braking hard enough, you can "beat the gun". Don't do it with anyone behind you or they'll get a macroscopic view of your license plate. Most of them are able to do the initial validiation in about 1/2 to 3/4 second, and then 2/10 of a second thereafter on subsequent checks, so your key is to start braking AS SOON AS your detector goes off. Note that you usually have less time when the radar gun is operating from a fixed position (Kustom's stationary-only guns like the Falcon are deadly in this respect - they can lock in about 2/10 second on the first fire). Moving mode guns have to validate two readings (the cop's ground speed as well as yours) so you have a bit more time, but still not much. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104