depolo@eniac.seas.upenn.edu (Jeff DePolo) (08/16/90)
In article <1229@atlas.tegra.COM> vail@tegra.COM (Johnathan Vail) writes: >Is this in anyway similar to the "CHiPs" detectors being sold? The >description was vague, something about being able to detect the cars >because of the mobile repeater in the car. The repeater is used to >allow a respectable range out of the walkys. I infer that the >detector works by either detecting the LO or by kerchuncking the >mobile repeater. Since a cop described the use of the detector as >being very illegal the kerchunking approach seems more likely. Many state police vehicles use what are known as "mobile extenders." Basically what they are is a small repeater that receives transmissions from the policeman's hand-held radio and relays them through the cruier's radio. It also repeats received transmissions through the mobile radio to the walkie-talkie as well. This transmit side is activated whenever a signal is received by the mobile radio. Since police frequencies are often active, the mobile extender transmits very often. The CHiPs detectors don't kerchunk the extenders. I'm sure the Friendly Candy Company would have come down hard on the manufacturers if they did. The CHiPs detectors are nothing more than glorified scanners. They scan the frequencies used for the mobile extenders' transmitter and sound an alarm when a signal is heard on that particluar frequency. Since the mobile extender transmitters are relatively low power (less than 100 mW, if I remember right), range is typically less than a mile, possibly a lot more on hilltops, etc. You can home-brew your own CHiPs detector from any scanner capable of receiving the mobile extender transmissions (which are typically on either the VHF-Hi or UHF police bands). Let the radio scan and whenever you hear a signal break squelch, you know you are in range of one of the mobile extenders. You could go through the trouble of having it "beep" instead of listening to the transmission, but it's probably not worth the effort. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia)