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Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ihnp4!kitty!larry
From: larry@kitty.UUCP
Newsgroups: sci.electronics,sci.physics
Subject: Re: Laser eavesdropping
Message-ID: <1683@kitty.UUCP>
Date: Mon, 6-Apr-87 00:19:04 EST
Article-I.D.: kitty.1683
Posted: Mon Apr  6 00:19:04 1987
Date-Received: Wed, 8-Apr-87 05:20:15 EST
References: <503@sw1e.UUCP> <704@brl-sem.ARPA> <16143@sun.uucp> <2632@phri.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 68
Keywords: modulation
Xref: utgpu sci.electronics:463 sci.physics:1051
Summary: Passive electronic eavesdropping devices...

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?

	It probably still is.  The microwave energy is probably being used
for at least three purposes:

1.	To excite passive tuned-cavity listening devices.  A sharply tuned
cavity is fitted with a metallic microphone diaphragm.  Microwave energy is
directed toward the cavity using a directional antenna from the monitoring
location.  The microwave oscillator is connected to the antenna using a
directional coupler having forward and reverse power detectors.  The
instantaneous VSWR is an indication of diaphragm displacement as the cavity
power absorbtion changes through detuning.  Modulation of the microwave
oscillator, with appropriate detection, can also be used to improve S/N ratio
of the detected signal.

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.  This technique may be implemented by a tuned
cavity that is fitted with a varactor diode leading to a second tuned
cavity at a higher frequency.  The second tuned cavity is fitted with a
metallic microphone diaphram.  The "retransmitted" frequency is often a
simple second or third harmonic of the excitation frequency; depending upon
the type of diode and what frequency at which it is designed to oscillate,
the retransmitted frequency can also be a small frequency shift of the
excitation signal.  This principle has been used for a number of years as
a passive military radar beacon (sans microphone :-).

3.	To measure the micro-displacement of some reflecting metal object
in the subject room; this displacement is presumably the result of sound
vibration within the room.  The reflected signal is modulated both by
sound amplitude and sound frequency; the reflected signal is detected as
phase modulation and corresponds to the instantaneous velocity of the
reflecting surface.  This technique has the advantage of no advance
"planting" of a listening device in the room.  The principle behind this
technique has been used for industrial vibration measurement for at
least 30 years.
  
> 	The story I heard (about as reliable as any Nth-hand info) was that
> the the Russians presented the American embassy folks with some sort of
> carved wood plaque of an american bald eagle, or something like that, as a
> gift.  Of course, the embassy folks gave it to the electronics types to
> look at to make sure it wasn't bugged and then hung it up in the office.
> It never occured to them that the sheet metal plate on the back of it might
> actually be a microwave reflector...  Memory is hazy, but I seem to
> remember hearing this 5-7 years ago, and the story was at least a few years
> old by then.  Believe it at your own risk.

	It's a true story, and it happened during the 1950's at the United
Nations; most people in the know call this "The Great U.N. Seal Caper". :-)
	It seems that the Russians gave the Secretary General of the U.N.
a nice wooden plaque which contained a passive-cavity listening device
whose principle I described in (1) above.  It operated undetected for at
least two years.  The frequency of operation was around 330 MHz (which is
not truly microwave, but the principle is still the same).  The Russians had
a high-power transmitter concealed in a truck that they would park in close
proximity to the the U.N. building when they wanted to monitor the device.
I don't know how much transmitting power was used, but considering the lack
of directivity at UHF frequencies I would guess it to be several hundred
watts CW.  I seem to recall that the device was discovered only because the
truck was discovered, thereby triggering a thorough search of the building.
	You have to admit, them Rooskies have balls. :-)

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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