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Eavesdropping using microwaves - addendum

11/12/2005 05:00 AM EST
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Sventhewonderyak
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re: Eavesdropping using microwaves - addendum
Sventhewonderyak   2/5/2010 9:37:03 PM
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I don't know. Try putting an rf signal of a low frequency on one of the strings of the harp using a small alligator clip connected to a wire and oscilator. Voices in the room should cause the harp string to vibrate which would then modulate the rf wave. With a radio receiver you could then listen in.

Sventhewonderyak
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re: Eavesdropping using microwaves - addendum
Sventhewonderyak   2/5/2010 9:29:06 PM
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The following is from a usenet post from 1987: In article <2...@phri.UUCP>, r...@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 40 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 guts. :-) As can be seen, your article is fairly well written but poorly researched. In addition, the Magrath patent has more to do with the politics of ignorance and potential financial gain more than anything else. Your article mentioned a commercial product called the Doppler Stethoscope. In regards to this device it was stated that it will not directly extract speech. I have first hand knowledge of this device and I can state without any doubt that it will in fact recover speech. Not from any great distance, but yes, it will do this. There are several different copies of this device that an electronics individual has been attempting on a website....try this out: http://projects2.gbppr.org/mil/index.html Look at the various links on the page especially at the bottom of the page. There are some recordings of the device operating with various levels of sucess. Basically, the priciple involves a device called an interferometer, which is just a fancy term for a beam splitter. To make one of these all you really need to do is take an rf signal and split it into two legs of different lengths with one beam being the reference and the other beam being the reflection and then recombine them and extract and demodulate the phase shift to recover the amplitude which contains vibrations caused by speech. You can do it with a couple of FRS radios and some odds & ends. The Led & Laser systems that do this, which were also invented by the Soviets by the way, use the same phase/demodulation scheme as well. There are also ultrasonic flood versions of these devices too, but I do not think they ever got much use. Hope this helps.

TechQuestions
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re: Eavesdropping using microwaves - addendum
TechQuestions   2/1/2010 2:16:48 AM
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Does anyone know how (or whether) an orchestral harp could be bugged? Or can you think of an instrument suitable for bugging--one not likely to be kept in a case most of the time (like a guitar), which might interfere with the task at hand? I'm writing a screenplay in which someone will bug another person's instrument (not while it's being played), but while it's in their apartment or car. Thanks to anyone who can help. Most photos I've found of orchestral harps don't show the sound holes I was looking for, through which a bug could be planted inside.

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