🚀 go-pugleaf

to sci.electroics and rec.autos:
jkimble@bally.Bally.COM (The Programmer Guy) writes:

Subject: Detecting Radar Detectors

>I saw a story on the world news a few weeks ago regarding drivers
>(primarily 18-wheelers) using radar detectors.  During the news
>segment, the reporter was talking to a highway patrol officer who was
>using a device to detect if the oncomming vehicle was using a radar
>detector.
>...How do these detectors of radar detectors work? ...

A friend sent me an article from a Virginia newspaper, _Lessburg 
Today_, July 13, 1990, entitled "Radar 'Detector Detictor' Cruises 
Local Primary Roads."

     "...The $1100 device detects microwaves "leaking" from operating 
     radar detectors...  Originally developed in Canada, where radar 
     detectors are illegal... The VX6-2 detector is being fornished at 
     no cost on a loan basis to the state police by the Insurance 
     Institute for Highway Safety, a private research organization 
     funded by insurance companies..."

There's a picture of the beast, which is housed in a box aprox. 3 x 4 
x 6", with two knobs and a LED on the front.  It looks home-brewed.

---

This article seems to confirm rumors that the insurance cartel wants 
to outlaw radar detectors everywhere in the U.S., either through the 
legislators they own, or by excommunicating/sh*tlisting policyholders 
who use them.

These devices have been used in Canada for several years.  They are 
for real, and apparently very effective.  

Superhet radar detectors work like little spectrum-analyzers: The 
local oscillator (11.5 GHz +/-) is a Gunn diode with a varactor to 
sweep its frequency.  The first i.f. is 1 GHz, followed by further 
conversion and circuits which detect valid alarm conditions.  K-band 
is detected via a harmonic of the local oscillator; I haven't done the 
arithmetic.  The advantage of this method is that it searches a wide 
band but retains high sensitivity.

The local oscillator, varactor and mixer diodes are all inside a 
cavity at the end of the horn antenna.  A series of screws projecting 
into the horn form a trap to suppress local oscillator radiation, but 
are only partially effective.  Some brands of radar detector mutually 
interfere because of local-oscillator radiation.

In WW II, the Germans installed radar detectors on U-boats.  These 
also had a problem with local-oscillator radiation, and Allied ASW 
aircraft were able to home-in on them without radar.

A detector-detector could probably be made by modifying a conventional 
 radar detector:  Mechanically retune its local oscillator to 1 GHz 
above or below 11.5 GHz, and remove the trap screws.

--

Frank Reid    W9MKV     reid@ucs.indiana.edu
26 states on 10 GHz.  ZAP!  ;-)