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From: sampson@attctc.Dallas.TX.US (Steve Sampson)
Newsgroups: sci.electronics
Subject: Re: "Spybuster" AD COPY
Summary: Thoughts on how it operates
Message-ID: <9047@attctc.Dallas.TX.US>
Date: 19 Aug 89 09:29:06 GMT
References: <17100002@inmet>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 13



A couple of thoughts on the Spybuster: 1) With that frequency range it
probably uses the ATC Transponder which transmits at 1090 MHz (1.09 GHz),
and 2) It doesn't reflect off the aircraft, it's transmitted by it.
3) It's probably an omnidirectional antenna (which has 360 degree coverage)
since no mention was made of an azimuth indicator.  Would this then be a
1090 MHz receiver with a signal strength meter and alarm threshold control?

The aircraft actually sends a burst of replies to ATC every time the
Transponder is interrogated.  By comparing the amplitude of the last burst
with the amplitude of the current burst would then be an indication of
closing/opening rate.  Just thinking out loud...