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Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!husc6!think!ames!lll-lcc!pyramid!pesnta!phri!roy
From: roy@phri.UUCP
Newsgroups: sci.electronics,sci.physics
Subject: Re: Laser eavesdropping
Message-ID: <2634@phri.UUCP>
Date: Mon, 6-Apr-87 09:21:19 EST
Article-I.D.: phri.2634
Posted: Mon Apr  6 09:21:19 1987
Date-Received: Thu, 9-Apr-87 00:59:01 EST
References: <16143@sun.uucp> <2632@phri.UUCP> <1683@kitty.UUCP>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 29
Keywords: modulation
Xref: utgpu sci.electronics:465 sci.physics:1058

In article <1683@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
> In article <2632@phri.UUCP>, roy@phri.UUCP (Roy Smith) writes:
> > > Wasn't the U.S. Embassy in Moscow being snooped on a couple of years
> > > ago with *microwaves* being bounced off windows?

	I didn't write that!  Larry, you may be an inexhaustible source of
useful information about all areas of communications and a cat lover (both
good things), but you have to learn to be more careful in quoting! 1/2 :-)

> 2.	To excite listening devices which use received energy to power a
> transmitter on a different frequency, which is then detected by a receiver
> at the monitoring location. [...] The "retransmitted" frequency is often a
> simple second or third harmonic of the excitation frequency ...

	This is also, BTW, one of the ways those stolen-item detectors in
stores work.  The big plastic clips contain some sort of passive tuned
circuit, with a diode detector.  The gizmos on either side of the door emit
RF at some frequency (presumably up in the several hundred Mhz range) and
listen for harmonics comming back.  The important features of this system
are that the replicated parts (the big plastic clips) 1) are cheap to
produce, 2) require no internal power, 3) are not likely to break, and 4)
can be made physically small.  The latter three are properties which also
makes this a nice spy technology.
-- 
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016

"you can't spell deoxyribonucleic without unix!"