It’s long been most drivers’ dream to go past a policeman with radar and blow up his radar gun. After all, the cops just use radar to generate revenue for the cities and towns across the country. It just doesn’t seem fair to penalize drivers for going just a little above the limit.
Over the years many people have designed (or tried to) systems to help defeat the radar traps. Some of these were just silly – remember the ‘put a fluorescent bulb across your windshield? – Oh, and put balls of aluminum foil inside your hubcaps? Others were more intentional radar jammers, electronic devices designed to interfere with the radar gun. Of course, the FCC was quick to adjust the rules to keep these off the street. Recently, Rocky Mountain Radar introduced radar scramblers, or ‘passive’ radar jammers. We thought it would be a good idea to explain all these efforts by telling you what they are and how they work.
Are You Kidding Me?
Some of the different methods to disable police radar are just silly when you think about them. For example, how can one believe that a fluorescent tube can magically absorb radar beams? While they will interfere with a radar gun and give a false reading when operating, there is no physical mechanism for anything like that when they are just laid on the dash.
Another popular thought was putting tin foil in the hubcap. This came from the World War II technology of dropping strips of metal foil from aircraft to hide from the enemy radar. Unfortunately, most hubcaps are made of metal or, now, chrome plated plastic. This means that when you put the metal foil between the hubcap and the steel wheel, there is no way for radar to penetrate inside to even see them. Further, as soon as the car starts moving, centrifugal force will keep all the balls stationary instead of ‘rattling around’ randomly to confuse the radar – that cannot even see them anyway!
Radar Jammers are basically transmitters tuned to be at or close to the police radar frequency. They have been deemed to be illegal by the FCC. The FCC defines a Radar Jammer as ‘…any device that contains an intentional radiator and emits radio frequency energy.’ An intentional radiator is a transmitter that generates its own radio frequency and emits it into the environment.
There are two Radar Jammer techniques that have been used for the consumer. The first is a simple transmitter tuned close to the police radar frequency that is turned On/Off (modulated) at a set frequency. The idea behind this approach is that the mixer diode in the radar gun will see the extra energy go up and down and amplify this change in its processor. If this works, the processor would effectively see the modulation and one could basically just dial in any speed they wanted. Naturally, there are a few problems with this approach. First, the amplitude variation is very small compared to the signal of the car so it is difficult to get enough for a reading. Second, when one sends out a speed lower than they’re actually going – the only reason to have a Radar Jammer – the transmitter beam from the jammer can actually increase the distance the police radar gets the correct speed! To cure this requires a very expensive isolator.
The second method is for the Radar Jammer to sweep across all the frequencies that the police radar can operate at. This approach was successfully used by Consumer Microwave Company in the late 70s to jam radar. The Radar Jammer was designed to function in an adjacent frequency band and ‘allowed’ to overlap the police band as well. It was sold with a caution “not to use on the highways” as it would completely jam police radar. This technique was marketed successfully until the police were allowed to use a newer super-wide Ka-band of the frequency spectrum. The technology was just too expensive to cover the added band.
Both of these Radar Jammer designs became challenged by the number of bands and their width to be able to economically operate and faded away.
The Radar Scrambler was a term coined by Rocky Mountain Radar to describe their passive radar jammer technology. The radar scrambler differs from a radar jammer in that it does not generate or transmit any radar signals. Rather, it works exactly the same way as police radar detects the speed of your car. Police radar bounces a radar signal off your car and, if the car is moving, that signal is distorted slightly. This is called the Doppler Shift and is proportional to the speed of the car. By mixing the bounced beam with the signal that was sent out, the radar gun can extract your speed information.
Due to a court case in Florida during the 60’s – when a tree was clocked going 75 miles per hour – all radar guns must now sample the speed reading 8 times and get the same reading before displaying it to the officer. The courts figured that the probability of a random reading – like those leaves on the tree in Florida – occurring 8 times in a row was very unlikely and the speed reading could be trusted.
A passive Radar Jammer – or Radar Scrambler – is mounted in your car and when the police radar beam hits it, it adds several ‘Doppler shifts’ to the signal that is being reflected back to the radar gun. The Radar Scrambler has a specially tuned antenna so all the radar signal is reflected back to the cop. When the police radar extracts the Doppler shifts from the reflected beam – and the one from your car – it sees the car’s speed plus all the other ‘speeds’ from the scrambler and gets confused. Since it cannot get the same reading every time, it does not display any speed to the officer.
Since the Radar Scrambler does not contain an intentional radiator, does not generate any radio frequency energy or transmit any signal at all, it fails the FCC’s definition of a Radar Jammer and is completely compliant with the FCC Rules and Regulations.
An added benefit is that the Radar Scrambler, unlike a Radar Jammer, can confuse police radar without setting off all the radar detectors in the vicinity!
Mike Churchman – President