pturner@eng.auburn.edu (Patton M. Turner) (06/24/91)
Dave Rubin <drubin@prism.poly.edu> writes: > I was wondering if it was possible to jam the signal of a cellular > phone to prevent effective communication. > The reason I ask is that a new automobile anti-theft system, called > "Intercept" has recently been introduced. This system uses a cellular > phone to alert a central station as to the whereabouts of the stolen > automobile, and the station can also send a signal to the car to turn > off its engine. > It would seem that if a car thief can get his hands on a device to jam > a cellular phone signal, the "Intercept" system would be useless. Virtually any reciever can be jammed when you are several orders of magnitude closer than the transmitter is (assuming a omnidirectional antenna or the ability to relocate the jammer). I suspect the strength of this device that it won't be expected. Several ways to defeat the device are: 1) Unplug the battery, the antenna, etc, after breaking into the car, the police probally won't respond too quickly because of false alarms. (An aside: a friend of mine who carries a lot of expensive radio equipiment in his car bought a Jeep with a factory alarm installed with sensors in the door, hood, etc., he's never had a false alarm.) 2) Burn out, overload or jam the front end of the reciever with a RF source near the cell-phone frequency fed into a high gain yagi antenna. The antenna can also be connected to the battery or a 110/220 VAC source. Bye Bye FET's! 3) If it's an external antenna, cut it. If the antenna is inside the car (ie. hidden in the trunk, or even worse under the hood), I would think parking the car inside a steel bulding would prevent reception of the signal. I think if I had one of these alarms, I would want it to page me rather than call the police. Of course, in Alabama we don't have too park to far from where we are going. Patton Turner KB4GRZ pturner@eng.auburn.edu