what is an effective RADAR/LASER jammer?

[AndrewR]

Jammers of any sort are illegal. The idea of a laser jammer might work, but it would be insanely expensive (you'd have to detect and locate the gun and send a fake signal or a jamming signal in VERY short order).

I know for a fact that you can build a radar jammer for use in a car because a friend of mine knew a guy who did just that (Air Force electronics warfare guy). He basically broadcast a specific speed to a cop's receiver so that he always appeared to be going 65 (or 55, don't recall which or if it could change). He ended up selling the car and forgot to tell the buyer that the rig would only broadcast that speed so the guy ended up with a ticket for doing 55 in a 25 zone.

 

[Ultima]

Have you never heard of the Autobahn? People there drive twice as fast as on highways over here yet their death rate per mile/km is less than over here. Most highways have their speed limits set far below the engineering limit or the 85th percentile limit.



<<

<< Following the speed limits (for those of us who would rather not waste such time) sucks. >>



Yes and it's the thrill seakers and irresponsible speeders that cost thousands of U.S. lives a year not to mention high insurance rates and increased medical expenses. GROW UP! :|

Any device to prevent law enforcement devices from getting a lock on your speed is illegal. Call your local police station and ask!

Any device that transmits radio waves that isn't FCC licensed (last time I checked, NO radar jammer was licensed!) is unlawful to operate. If you're caught, you face insurmountable financial burden and legal issues.

Speeding doesn't save as much time as you think. I'm talking about going ten to fifteen miles over the highway limit which a lot of the time people do because of traffic flow. People that go 100 mph on the highway that get caught deserve what's coming to them. :|

Cheers! >>

 

[Freejack2]

Radar/lidar jammers are a joke, only things I know of that work is to get a good detector like the Valentine One, supposedly some of those license plate covers work giving you a couple of seconds before the cop retargets another part of your car with lidar, and keep a lawyer on retainer.

 

[Ultima]

<< Jammers of any sort are illegal. The idea of a laser jammer might work, but it would be insanely expensive (you'd have to detect and locate the gun and send a fake signal or a jamming signal in VERY short order).

I know for a fact that you can build a radar jammer for use in a car because a friend of mine knew a guy who did just that (Air Force electronics warfare guy). He basically broadcast a specific speed to a cop's receiver so that he always appeared to be going 65 (or 55, don't recall which or if it could change). He ended up selling the car and forgot to tell the buyer that the rig would only broadcast that speed so the guy ended up with a ticket for doing 55 in a 25 zone. >>



I don't think that's how a laser jammer could operate at all.
What you could do is apply some material to the car's body that will diffuse the laser. That way, it isn't reflected directly back to the cop, but is reflected EVERYWHERE causing the cop to get a very weak and inaccurate signal. I wonder if this is possible...

 

[jteef]

Broadcasting a constant speed would require extremely complex circuitry since it would have to constantly adjust its own frequency based on how fast you are driving. I doubt that is what the guy did.

I am not sure if laser uses time of flight or the doppler effect to measure speed. If its the former, you could probably equip your car with a laser diode on the same wavelength as the gun and it would give false readings. broadcasting light is perfectly legal. The actual units in use are probably not that simple and would require a lot of test equipment or access to a service manual to make something that actually worked. There are a lot of easy things they can do to detect a certain signature they embed on the outgoing light that would be difficult to reproduce without a lot of specific knowledge.

A car with a low profile and no front licence plate or licence plate holder will give the cop a pretty tough time in getting an accurate laser reading. An unlicenced RF transmitter is definitely illegal, but i dont know how much you can get away with before anybody notices or how much power you would need to be effective. Using a jammer over a wide band like Ka might also be pretty tough. If they use a lot of averaging you could probably build a circuit that sensed the incoming frequency and quickly auto tuned a transmitter to jam. It would have to do that *really* quickly though. radio waves travel pretty quickly through the air... A good radar detector and knowing the law regarding what is required and allowed to convict you of speeding are pretty effective in keeping you out of trouble.

jt

 

[AndrewR]

Broadcasting a constant speed would require extremely complex circuitry since it would have to constantly adjust its own frequency based on how fast you are driving. I doubt that is what the guy did.

Considering that the guy maintained extremely complex circuitry designed to do a lot more than simply spoof a police radar, I suspect it was well within his abilities. We're talking about a military electronics warfare specialist, not a college student.

 

[Fandu]

AFAIK Radar guns use the doppler effect to determine speed, so it would be very easy to make such a system. As long as you knew the frequency of the guns, it's pretty simple math to determine what frequency you should broadcast back at.

Eg: Say radar is 600Hz, if you always wanted to be going 100km/h, you would broadcast at 649.02Hz

Now that's assuming that the cop is stationary. But it still wouldn't be too hard to detect an incoming frequency, apply the correct shift and re-broadcast it. If you know the exact frequency of the radar guns, then it's even easier. That's not exactly too hard to find out either.

 

[Jerboy]

<< They are illegal in CA. OK. MN. VA. NE. and Washington D.C. >>



It depends on the type of the jammer. If it simply reflects by a mean of reflector without the use of an RF amplifier it should be in compliance. Anything that uses RF generator or RF amplifier and creates RF energy from itself are in violation of Federal Communication Commision laws.

Radar Detectors are illegal in commercial vehicles per Federal Law
Link

 

[spanky]

hehe... don't get the jammer with a 20 ft range

 

[Lucky]

<<

<< They are illegal in CA. OK. MN. VA. NE. and Washington D.C. >>



It depends on the type of the detector. If it simply reflects by a mean of reflector without the use of an RF amplifier it should be in compliance. Anything that uses RF generator or RF amplifier and creates RF energy from itself are in violation of Federal Law(FCC).

Radar Detectors are illegal in commercial vehicles per Federal Law
Link >>





he didnt say detector he said jammer. detectors are only illegal if you have are driving on a CDL or are in virginia.

 

[jteef]

<< Eg: Say radar is 600Hz, if you always wanted to be going 100km/h, you would broadcast at 649.02Hz >>



That would only work if you weren't moving either.

now tell me how to do that if instead of 600hz its any frequency between 18 and 31Ghz. What if they modulate the signal with a triangle wave? or a recording of the first 10 seconds of the 1812 overture? or the last 2 seconds of ambient noise recorded by the radar unit? a really powerful wideband noise which would probably be effective on police radar(prolly not military) up until the point you were arrested for using an unlicenced rf transmitter.


jt

 

[vegetation]

There is some confusion here. Traditional radar jammers are indeed illegal. However, laser jammers are NOT illegal. In fact, traffic laser's infrared emissions are regulated by the FDA (due to potential damage to human eyes), not the FCC! And they do work if mounted properly, I have been saved many times with my plate mounted laser sensor and emitter array.

 

[AgentZap]

They don't work. I have a passive jammer and I go by those "You are going this fast" automated radar guns on the side of the road, and they get my speed right every time. Like everyone says it is probably the best idea to get a solid detector like the V1 and keep your eye out and make sure nobody paces your car.

 

[Theslowone]

I have talked to many cops about most jammers, and all of them laugh at jammers. For one thing they say they don't work, the next thing is they are pretty good judge of speed, this judgement increases when your passing someone they just clocked at 80 like they were sitting still.

 

[sharkeeper]

<< now tell me how to do that if instead of 600hz its any frequency between 18 and 31Ghz. What if they modulate the signal with a triangle wave? or a recording of the first 10 seconds of the 1812 overture? or the last 2 seconds of ambient noise recorded by the radar unit? a really powerful wideband noise which would probably be effective on police radar(prolly not military) up until the point you were arrested for using an unlicenced rf transmitter. >>



Well if you want to go to that trouble...


Why not construct a device that disables the entire electrical system of the police cruiser? This way you can drive the way you want. When you see flashing lights, just disable them and speed away laughing!

I like the idea of using a TFT panel mounted where your license plate is. This allows you to use any license plate you want, make it blank while running automated toll booths and intersections where red light cameras take your picture. Imagine your tag changing to some nasty picture or video clip of your choice to display at a tailgater! Today's pocket pc's are all that are needed to provide the display information. The uses are only limited by your imagination!

Cheers!

 

[BillGates]

I used to frequent a particular sportbike website as I'm a rocket rider myself... One guy who was there worked for the Army and painted his entire bike with the brown paint that they paint tanks with to basically absorb radar.... He said the stuff is like $500 a gallon or something - and ugly as sin, but definitely effective... Pretty sweet.

 

[rutchtkim]

just watch out for the cop speed pacing u secretly on the highway, a time when the jammer cant help u out. happened to me, sux

 

[Fandu]

<< That would only work if you weren't moving either. >>



The doppler effect is expressed by the following formula for relativistic speeds. My example was non-relativistic BTW
V/c = dF/Fo

where V is different in velocity between the two refrence frames
c is the speed of light (3x10^8m/sec)
dF is the change in frequency
Fo is the source frequency

27.777/3x10^8*18x10^9 = 1666.62Hz change, so if the source frequency is 18GHz, you would broadcast at 18000001666.62Hz

31GHz would be 31000002870.3Hz for 100.0Km/h

So what you would need to do is detect the incoming frequency and apply a relativistic doppler effect. It doesn't matter if your both moving, or only one of you, etc. The effective change in the frequency is the same regardless.

 

[jteef]

Fandu, if you transmit while moving, the perceived frequency to a bystander will be different than the one you are broadcasting based on how fast you are going. That is why you couldn't easily broadcast an absolute speed. The doppler effect works both ways.

if you are really screaming on a bike in the middle of nowhere, you already get at least a minute head start and chances are the cop isn't going to be able to read your plates. The military does have some amazing stuff though...

jt

 

[Fandu]

If we were dealing with non-realtivistic speeds, then yes you would be correct. However, because we're using EM radiation (radar/light) with a speed of c, you have to use special relativity.

Think of it this way. It doesn't matter if your moving, or the cop is moving, all that matters is the relative velocity between the 2 of you. See formula I posted earlier. Now if we know the broadcast frequency, whether we detect it, or know it, we take that and apply a doppler shift. Remember that there are 2 doppler shifts involved here. One when the EM hits your vehicle, and another it gets back to the detector. So if you always wanted to be traveling at 100km/h, the shift when the waves hit your vehicle is ALWAYS the same. Now remember that the detector also takes into account the speed of the cop car when it calculates the speed. So if the cop is sitting still, you broadcast a shift corresponding to 100km/h, and that's what the detector reads. If both you and the cop are moving, the detector will receive a shift equal to 100km/h plus it's own speed. It knows it's own speed and takes that into account when it calculates the relative speed. It works

Obvisouly you wouldn't broadcast the same frequency behind you.....


See: Halliday, Resnick, & Krane. Chapter 39, section 6: The Doppler Effect for Light.

It has a decent explanation as well as the derivation. Notice that the formula that I used is a simplified one based on the fact that the ratio of V^2/c^2 is very, very small (8.6x10^-16). So it's a pretty good approximation.