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From: Zerothehero2...@webtv.net
Newsgroups: sci.electronics.design
Subject: Microwave Listener System
Date: Thu, 13 Dec 2001 13:06:16 -0800 (PST)
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I am interested in the specifications on the microwave surveillance
systems used by the government and others to monitor room sounds from a
remote location. These systems are similar in principle to the laser
window bounce listener systems that are well known, but because they are
utilizing microwaves or millimeter waves they can and do penetrate solid
barriers and so do not require a window for operation. 

I only have an interest in the type of microwave/millimeterwave passive
reflector that does not require the implantation of a resonant cavity or
other similar device in the area of interest to be able to function. 

These devices have existed for over 3 decades, but specific information
such as exact carrier frequencies, power output levels, etc, are very
hard to obtain. I know that commercial units, even from the early or mid
70's were very small, only several inches by several inches in size.
This small unit performed both the transmit & receiver demodulation
function. I call it - sound radar.

I think the units that operate without a planted resonator are utilizing
a principle where by standard everyday objects in the dwelling to be
monitored, including the people themselves, modulate a continues wave
microwave or millimeter wave carrier with the amplitude as well as the
frequency of the audio sounds produced in the dwelling of interest. This
now modulated carrier wave is then bounced back to the transmit/receiver
unit and then demodulated as an AM or possibly a PM signal. 
There are government people, others etc...that will claim a device like
this cannot work with out a purpose built resonant cavity being planted
in the area to be monitored. This kind of claim is either propaganda to
keep the reality of such devices hidden, or is made out of ignorance.  

I would like to obtain brand & model names, companies that sell the
units, as well as full specifications as detailed in manufactures
product manuals etc. Any information would be appreciated.