commgrp@silver.bacs.indiana.edu (12/09/89)
I decided to post this here, where the smart people hang out. :-) There has been a long discussion on rec.autos about the Canadian radar detector-detector which the Dudley Do-rights use for sniffing out illegal radar detectors in peoples' cars (followed by fines and confiscations). It works by detecting 11.5 GHz local-oscillator radiation. Most superhet radar detectors apparently copy Cincinatti Microwave's basic design with 1-GHz first i.f. A harmonic of the local oscillator is used to detect K-band radar. Has anyone actually seen the infernal Canadian device? What does it look like? What is its range? Many brands of radar detectors mutually interfere because of local- oscillator radiation. Some of the Gunn-diode oscillators can be mechanically retuned down to 10.5 GHz. Has anyone tried to make a detector-detector by retuning an ordinary detector's local oscillator to 12.5 GHz and removing the series of screws in the horn antenna which form a trap to suppress 11.5 GHz transmission? It could be a fun project, useful for an *sshole early-warning indicator and other ECCM experiments. Unfortunately, you could not use a conventional radar detector simultaneously. Local oscillators in radar detectors include a varactor diode which sweeps their frequency, searching a few hundred MHz either side of the 10.525 GHz police radar frequency. Radar transmitters drift with age, temperature and voltage, and sometimes the cops (illegally) retune them, attempting to evade detectors. I don't know if detectors sweep continuously, or "lock on" when they detect a signal. There might be problems trying to use a sweeping detector to detect another swept signal. An extremely useful tool for such work is an X-band wavemeter. It's an adjustable resonant cavity with a tuning-screw calibrated in GHz. It has two waveguide flanges, one for input and the other for a diode detector. Tune for maximum output, read the frequency dial. I got one at a hamfest for $35. -- Frank Reid W9MKV reid@gold.bacs.indiana.edu