wiz@xroads.UUCP (Mike Carter) (07/27/89)
Hmm. The Ontario police department must be feeling a budget crunch. While I'm skeptical that a resonant cavity "Grid-dip" scan would come anywhere near being effective (lookit all those nice cavities on radiator grilles) the spectrum search for local oscillators operating near the typical radar detector frequency would. I wonder if there's a method to fake those out by jamming the spectrum full of high energy radio transmission...say in the 800MHZ range? Would a cellular phone transmitter start the lights on these detectors? My Mobile 2M FM Xmtr sets off my Radar Detector if it's on high power. In Australia during the 60's, the local government required a license for T.V. reception. They would be seen driving up and down streets in a white van with a loop antenna searching for houses with receivers using the same principles and confiscate the T.V is the owner(s) refused to cough up the price of a fine + a license. [ We were visited...my recently arrived from the States parents had no idea about the license bit ] Has anyone devised an effective method to "jam" the radar detector detectors? -- ============================================================================= = Mike Carter N7GYX, Phoenix AZ| Q: Why did the Chicken cross the road ? = = hplabs!hp-sdd!crash!xroads!wiz| A: To ESCape the Main Menu . = =============================================================================
karn@epic.bellcore.com (Phil R. Karn) (02/21/91)
It seems to me that there are some simple counter-counter-measures for the radar detector detector problem. Radar detector detectors work by sensing the stray radiation from the first local oscillator in the radar detector. The stray radiation leaks through the first mixer and comes out the antenna. 1. Use an RF amplifier. Amplifiers tend to be one-way devices; not only would a good one suppress LO energy, but it would improve receiver sensitivity. 2. Use a balanced mixer. A balanced mixer, by design, suppresses LO energy from going out the input port. Cheap unbalanced mixers simply combine the RF and LO signals and feed them to a nonlinear amplifier, and there's nothing to keep the LO energy from going right out the antenna. 3. Spread the LO before feeding it to the first mixer. Then despread the IF signal. Any stray LO radiation will also be spread, thus making it much more difficult (if not impossible) to detect. Spreading should be easy to do - use a common PN sequence generator for both the spreading and despreading operations. This will also require two additional balanced mixers, one each for spreading and despreading. Phil