Passive Resonant Cavity & "Spycatcher" Technical Surveillance Devices


Excerpt from the National Security Agency Museum Website

On August 4, 1945, Soviet school children gave a carving of the Great Seal of the United States to U.S. Ambassador Averell Harriman.  It hung in the ambassador's Moscow residential office until 1952 when the State Department discovered that it was 'bugged.'

The microphone hidden inside was passive and only activated when the Soviets wanted it to be.  They shot radio waves from a van parked outside into the ambassador's office and could then detect the changes of the microphone's diaphragm inside the resonant cavity.  When Soviets turned off the radio waves it was virtually impossible to detect the hidden 'bug.'  The Soviets were able to eavesdrop on the U.S. ambassador's conversations for six years.

Excerpt from Spycatcher, by Peter Wright

Taylor and I divided up the technical work.  The Post Office pressed ahead with research into infrared detection.  I began using the resources of the Services Electronics Research Laboratory to develop new microphones and look into ways of getting sound reflections from office furniture.  I was already familiar with the technical principles of resonance from my antisubmarine work.  When sound waves impact with a taut surface such as a window or a filing cabinet, thousands of harmonics are created.  The knack is to detect the point at which there is a minimum distortion so that the sound waves can be picked up as intelligible speech.

One day in 1951 I received a telephone call from Taylor.  He sounded distinctly agitated.

"We've been beaten to it," he said breathlessly.  "Can we meet this afternoon?"

I met him later that day on a park bench opposite the Foreign Office.  He described how the British Air Attache in our Embassy in Moscow had been listening to the WHF [sic] receiver in his office which he used to monitor Russian military aircraft traffic.  Suddenly he heard the British Air Attache coming over his receiver loud and clear.  Realizing the Attache was being bugged in some way, he promptly reported the matter.  Taylor and I discussed what type of microphone might be involved and he arranged for a Diplomatic Wireless Service engineer named Don Bailey to investigate.  I briefed Bailey before he left for Moscow on how best to detect the device.  For the first time I began to realize just how bereft British Intelligence was of technical expertise.  They did not even posses the correct instruments, and I had to lend Bailey my own.  A thorough search was made of the Embassy but nothing was ever found.  The Russians had clearly been warned and turned the device off.

From questioning Bailey on his return it was clear to me that this was not a normal radio microphone, as there were strong radio signals which were plain carriers present when the device was operating.  I speculated that the Russians, like us, were experimenting with some kind of resonance device.  Within six months I was proved right.  Taylor summoned me down to St. James's Park for another urgent meeting.

He told me that the U.S. State Department sweepers had been routinely "sanitizing" the American Ambassador's office in Moscow in preparation for a visit by the U.S. Secretary of State.  They used a standard tunable signal generator to generate what is known as the "howl round effect," similar to the noise made when a radio station talks to someone on the telephone while his home radio or television is switched on.  The "howl round" detected a small device lodged in the Great Seal of the United States on the wall behind the Ambassador's desk.

The howl frequency was 1800 MH [sic], and the Americans had assumed that the operating frequency for the device must be the same.  But tests showed that the device was unstable and insensitive when operating at this frequency.  In desperation the Americans turned to the British for help in solving the riddle of how "the Thing," as it was called, worked.

Brundrett arranged for me to have a new, secure laboratory in a field at Great Baddow, and the Thing was solemnly brought up by Taylor and two Americans.  The device was wrapped in cotton wool inside a small wooden box that looked as if it had once held chess pieces.  It was about eight inches long, with an aerial on top which fed into a cavity.  Inside the cavity was a metal mushroom with a flat top which could be adjusted to give a variable capacity.  Behind the mushrooms was a thin gossamer diaphragm, to receive the speech, which appeared to have been pierced.  The Americans sheepishly explained that one of their scientists had accidently put his finger through it.

The crisis could not have come at a worse time for me.  The antisubmarine-detection system was approaching its crucial trials and demanded long hours of attention.  But every night and each weekend I made my way across the fields at the back of the Marconi building to my deserted Nissen hut.  I worked flat out for ten weeks to solve the mystery.

First I had to repair the diaphragm.  The Thing bore the hallmarks of a piece of equipment which the Russians had rushed into service, presumably to ensure it was installed before the Secretary of State's visit.  They clearly had some kind of microscopic jig to install the diaphragm, because each time I used tweezers the thin film tore.  Eventually, through trial and error, I managed to lay the diaphragm on first and clamp it on afterward.  It wasn't perfect, but it worked.

Next I measured the length of the aerial to try to gauge the way it resonated.  It did appear that 1800 MH was the correct frequency.  But when I set the device up and made noises at it with an audio-signal generator, it was - just as the Americans had described - impossible to tune effectively.  But after four weekends I realized that we all been thinking about the Thing upside down.  We had all assumed that the metal plate needed to be opened right out to increase resonance, when in fact the closer the plate was to the mushroom the great the sensitivity.  I tightened the plate right up and tuned the radiating signal down to 800 megacycles.  The Thing began to emit a high-pitched tone.  I rang my father up in a state of great excitement.

"I've got the Thing working!"

"I know," he said, "and the howl is breaking my eardrums!"

I arranaged to demonstrate the Thing to Taylor, and he traveled up with Colonel Cumming, Hugh Winterborn and the two American sweepers.  My father came along too, bringing another self-taught Marconi scientist named R. J. Kemp, who was now thier Head of Research.  I had installed the device against the far wall of the hut and rigged up another monitor in the adjoining room so that the rounds of the audio generator could be heard as if operationally.

I turned the dials to 800 and began to explain the mystery.  The Americans looked aghast at the simplicity of it all.  Cumming and Winterborn were smug.  This was just after the calamity of the Burgess and Maclean affair.  The defection to the Soviet Union of these two well-born Foreign Office diplomats in 1951 caused outrage in the USA, and any small way in which British superiority could be demonstrated was, I soon realized, of crucial importance to them.  Kemp was very flattering, rightly judging that it would only be a matter of time before Marconi got a contract to develop one themselves.


Within eighteen months we were ready to demonstrate the first prototype, which was given the code name SATYR.  Kemp and I presented ourselves at the front door of MI5 headquarters at Leconfield House.  Hugh Winterborn met us and took us up to a spartan office on the fifth floor and introduced a tall, hunched man wearing a pin-striped suit and a lopsided smile.

"My name is Roger Hollis," he said, standing up from behind his desk and shaking my hand stiffly.  "I am afraid the Director General cannot be with us today for this demonstration, so I am standing in as his deputy."

Hollis did not encourage small talk.  His empty desk betrayed a man who believed in the swift dispatch of business.  I showed him the equipment without delay.  It comprised a suitcase filled with radio equipment for operating SATYR, and two aerials disguised as ordinary umbrellas which folded out to make a receiver and transmitter dish.  We set SATYR up in a MI5 flat on South Audley Street with the umbrellas in Hollis' office.  The test worked prefectly.  We heard everything from test speech to the turn of the key in the door.

"Wonderful, Peter," Hollis kept on saying, as we listened to the test.  "It's black magic."

Excerpt from Marty Kaiser's Website

One type of free-space transmitter, a type that has no battery, is the so-called "resonant cavity" transmitter.  The Great Seal of the United States in the Moscow Embassy concealed such a device.  As has been reported extensively in the media, a wooden wall plaque was presented as a gift along with the suggestion of mounting it on the wall behind the Ambassador's desk.  Many may recall the photograph of Ambassador Lodge pointing to a "bug" concealed in the back of the plaque.  The embarrassment caused by the detection of this transmitter motivated the intelligence community to spring into action and devices similar to it soon evolved.

The resonant cavity transmitter is an amazingly simple device technically known as a passive radiator;, i.e., one that lacks an internal source of energy.  In constructing this device, a layer of thin metalized material was stretched across a closed metal tube.  The specific size of the tube determined its resonant frequency.  A wire "tail", which functions as an antenna, is attached to the base of the cavity.  The cavity was then flooded with a beam of radio frequency energy from an external source (usually in the microwave region, 1 GHz and up).  The size of the cavity and the length of its antenna are carefully calculated so that a harmonic (multiple) of the inbound radio frequency energy that bathes the cavity is rebroadcast.  The metalized diaphragm acts as a transducer, and the audio range energy modulates the returned radio frequency signal that, in turn, is picked up by a receiver in the nearby listening post.  Do not assume these devices are the sole providence of Federal level agencies.

Excerpt from Odyssey of an Eavesdropper, by Marty L. Kaiser

The most famous listening device [Leon] Theremin invented was found in the U.S. embassy in Moscow, hidden inside a wooden carving of the Great Seal of the United States.  It was presented by a group of Russian schoolchildren to the U.S. Ambassador to Moscow, Averill Harriman, in 1946, shortly after the end of World War II in Europe, at a time when Stalin was consolidating his conquests within th Iron Curtain bloc.  The Great Seal bugging coincided with start of the Cold War in earnest.  The device, known as "The Thing" in intelligence circles, hung on a wall in the ambassador's private study.  It was far ahead of its time because it carried no wires, electrical circuits, or batteries to wear out.  Its inherent genius was its simplicity.

It worked by beaming an ultra-high frequency radio signal at the Great Seal from a van parked near the building.  The room conversation entered the carving in holes drilled below the bald eagle's beak.  The radio frequency signal from the van was picked up by a short antenna that entered the device, which looked like a small tunafish can.  On one side of the can, a resonant cavity held a thin metallic membrane that vibrated at a rate determined by the voices striking it.  The signal carrying the room conversation then returned to the van at three times the frequency of the original input signal, was detected, monitored, and recorded.  Soviet intelligence was able to record conversations for nearly six years until the device was discovered during a routine physical, not electrical, security check.


On one occasion, [Chris] Griffin asked if I could check Helen's [Bentley] campaign headquarters.  Again, I found nothing.  The phones were of a newer design that contained a CPU (central processing unit) to handle the switching.  I showed the staff how easy it was to bug those phones by simply pointing my 2010 Doppler Stethoscope at the CPU and listening to the conversation.  Look Ma, no hands, no wires.  The staff was amazed at the ease with which their phones could be compromised.

Here are some internal photos of a Martin Kaiser 2010 Doppler Stethoscope.  The Gunnplexer is a M/A-Com 87140-2, which puts out 25 mW (+10 VDC) at 10.25 GHz.  The MA86551 (or similar) horn antenna provides an additional 17 dB of gain.  This stethoscope model is meant to matched with the Martin Kaiser 1059 Preamplifier but the 2047 Ultrasonic/Contact Stethoscope will also work.

Excerpts from The Art of High-Tech Snooping, Time Magazine, April 20, 1987

Moreover, inspections of the new U.S. embassy building now under construction have turned up plenty of signs of bugs: cables seemingly unconnected to anything, odd indentations in wall panels, steel reinforcing rods so arranged as to convert structural pillars into antennas.


For a long time American experts have worried about mysterious low-level microwaves that have apparently been beamed at the embassy building.  One explanation involves a possible type of snooping that does not require hidden transmitters in the building.  Mysterious cavities along with configurations of steel rods and wire mesh have been found in the walls of the new embassy complex.  It is theoretically possible that the microwaves could somehow pick up the reverberations that emanate from within the walls of a building; a computer would then analyze those reverberations.

Excerpt from Bugging the Bedroom, Esquire Magazine, May 1966

It's an automobile spotlight.  But inside: a Doppler radar microphone hooked up to the car's radio.  The car is parked miles away from your house, but in line of sight of your window.  A narrow band signal is bounced off the windowpane, which vibrates as you talk inside.  The driver hears what you say.

Excerpt from How They're Watching Us, Popular Mechanics, July 1976

Early this year the United States protested against the Soviet practice of radiating the upper floors of our Moscow embassy with microwaves.  Though our diplomats didn't say so, it was thought that the Russians were either trying to reduce the effectiveness of antennas on the embassy roof (antennas for monitoring equipment) or were using microwaves in an attempt to intercept conversations.

Microwaves are short radio waves that travel by line of sight, like FM transmissions.  They are employed in long-distance telephone communications, in radar operations and in the latest type of home cooking oven.  They also are used in connection with resonators to eavesdrop on conversations in rooms that are in the line of sight of the listening post.  Resonators - small metal canisters or metal sheets - may be buried in the walls, ceiling or floor of a room.  Metal wastebaskets, airconditioning ducts or other metal devices also funtion as resonators.

A resonator vibration in response to pressure changes in the air, changes produced by sounds, include conversation.  When microwaves hit a resonator, they "pick up" the vibrations.  Reflected, the beam travels back to the receiver operated by the eavesdropper.  Electronic processing is then used to reproduce the spoken words.

Excerpt from Moscow Station, by Ronald Kessler

In September 1952, near the end of [George] Kennan's brief tour, two technicians arrived from Washington to check further for bugs.  Having found nothing, they asked the ambassador if he would go through the motions of dictating to his secretary in the den.  Perhaps the sound of his voice would activate the bugs.  As he later reported:

I dronded on with the dictation [as] the technicians circulated through other parts of the building.  Suddenly, one of them appeared in the doorway of the study and implored me, by signs and whispers, to "keep on, keep on."  He then disappeared again but soon returned, accompanied by his colleague, and began to move about the room in which we were working.  Centering his attention finally on a corner of the room where there was a radio set on the table, just below a round wooden Great Seal of the United States that hung on the wall, he removed the seal, took up a mason's hammer, and began to hack to pieces the brick wall where the seal had been.  When this failed to satisfy him, he turned these destructive attentions on the seal itself.

In the seal the technicians found a cavity resonator that modulated microwaves beamed at it from the building across the street.  By converting the reflected beams back into sound waves, the Soviets could reproduce every sound in Kennan's office.

The day after finding the bug, Kennan noticed that his Soviet servants were unusually quiet, even hostile.  The tranquil mood of Spaso House had been shattered.  The thought of offending them weighed on him.  Perhaps, he thought, he should not have assisted the technicians after all.

Excerpt from The Age of Electronic Messages, by John Truxal

In the late 1960s, officials at the U.S. embassy in Moscow suddenly learned that the Russians had been using ingenious technology to listen to conversations in the ambassador's office.  On the office wall there was a plaque representing the American eagle.  The Russians had secretly hollowed out a cavity in the plaque and covered the front of the cavity with a membrane in such a way that it would not be noticed from inside the room.

Across the street, the Russians had a high-frequency radio with the beam focused on the cavity in the eagle.  Using the principle of resonance, they were able to listen to conversations with no "bug" or microphone in the ambassador's office, and indeed, no obvious way for the Americans to discover that the eavesdropping was going on.


Let us return to the opening paragraph of this chapter, where we mentioned the American eagle in the ambassador's office of the U.S. embassy in Moscow.  How did that system use resonance?

The below figure shows that the important parts were the cavity and the diaphragm.  The cavity was simply an empty space lined with metal.  This cavity was resonant for radio signals beamed at it.  The longer the distance D from the front of the cavity to the back, the lower the resonant frequency.

This resonance depending on size is just like sound signals resonating in organ pipes.  The long pipes resonate at low frequencies, the short at high frequencies.  A crystal glass partly filled with water acts the same way: the more water, the smaller the air cavity above the water, and the higher the frequency.  Thus, the cavity in the eagle was a resonant system, with the resonanting frequency measuring D.

From across the street, the Russians beamed toward the eagle a radio signal with many different frequency components.  The echo coming back to them was strongest at the resonant frequency of the cavity.

During conversation in the ambassador's office, the speech sounds are really changes in air pressure. When

  1. Air pressure rose, then
  2. the diaphragm in the figure was pushed to the right, and
  3. the resonant frequency of the cavity increased (smaller D), and
  4. the radio echo that the Russians picked up across the street was at a higher frequency.

Thus, the frequency of the echo received across the street directly measured the changes in air pressure or sound in the room.  The Russians could listen to the conversation, but the only indication that the Americans had of this very elegant bugging was an extra, very weak radio signal, which probably could not be easily detected unless the frequency was known.

Excerpt from Spycraft, by Robert Wallace and H. Keith Melton

The Technical Services Staff was not a year old in 1952 when the CIA received information about an alarming audio discovery in Moscow.  During an electronic sweep, the countermeasures team discovered a device secreted in the wooden replica of the Great Seal of the United States that hung behind Ambassador George Kennan's desk in his residence at Spaso House, barely a mile from the Kremlin, at No. 10 Spasopeskovskaya Square.  The seal had been hanging there seven years, after a group of Soviet Young Pioneers presented it as a token of friendship on July 4, 1945, to then U.S. Ambassador, W. Averell Harriman.  The gift, presented by smiling children in neatly pressed uniforms, concealed a listening device that would baffle and frustrate the Agency for years.  "The Englishmen will die of envy," Valentin Berezhkov, Stalin's personal translator, whispered to Ambassador Harriman during presentation.


However, what was discovered hanging behind the Ambassador's desk in 1952 was revolutionary in the technology of listening devices.  Implanted in the middle of the carved wood of the Great Seal, cleverly hidden behind an air passage formed by the American eagle's nostril, was a device that was alarming as much for the technology it employed as the fact it had been active for more than half a decade.  Indeed, four American ambassadors - Averell Harriman, Walter Smith, Alan Kirk, and George Kennan - presumably had their secret conversations picked up by the bug.

Differing significantly in design and function from any piece of covert listening equipment previously known, the device was constructed of precision-tooled steel and comprised a long pencil-thin antenna with a short cylindrical top.  Agency engineers could not understand exactly how it worked.  The stand-alone unit, apparently, did not require a battery or an other visible power source.  It had no wires or tubes, nothing that identified the device as a piece of electronic equipment.  If the oddly shaped length of metal was tranmitting conversation, then how was it doing it?

"The Thing," as it was soon dubbed, bounced among the Agency's lab, the FBI, and private contractors for evaluation and reverse engineering.  No one could offer anything beyond an educated guess to how The Thing worked, and somewhere in its travels from lab to lab it was damaged from either improper handling or shipping.

The Thing was eventually sent to Peter Wright, the principal scientist for MI5, the British intelligence service responsible for counterintelligence operations.  Wright worked for more than two months to solve the mystery before eventually coaxing it into operation.  He dubbed it a "passive cavity resonator."  The Thing, as Wright discovered, worked by reflecting radio waves, then picking those echoes up with a radio receiver.

To operate the device, the NKVD aimed a continuous 800 MHz radio signal at the seal from a listening post in the building across from Spaso House.  The Thing's thin diaphragm at the top, which Wright had repaired, vibrated with the sound of a voice.  Those vibrations were carried by an interior tuning post to the antenna.  Then, as the vibrations hit the antenna, they altered the reflected radio signal that bounced back to the listening post.  The Thing did not require internal power in the same way a mirror does not require power to reflect light.  The radio transmitter and receiver, code named LOSS (or REINDEER by the Russian techs), were a marvel of signal processing, considering the technology available at the time.

According to Wright's own account, once he understood the principle and made the device work, he took another eighteen months to create a similar system for British intelligence.  Called SATYR, his device featured aerials - transmitter and receiver - disguised as two proper British umbrellas.  SATYR proved to be a great success and Wright called it "black magic."  Then, as he observed, "the Americans promptly ordered twelve sets and rather cheekily copied the drawings and made twenty more."  The American version of the device, according to Wright, was called EASY CHAIR (also called MARK2 and MARK3).

Excerpt from Molehunt, by David Wise

But the CIA's technical boffins worked hardest of all at playing catch-up with the KGB: they were trying deperately to reproduce an unusual, highly sophisticated bug that the Soviets had used against the United States with devastating effect.  The bug employed a technology that had not been encountered before, and the CIA scientists were having trouble figuring it out.

In 1945, the Soviets had presented to Ambassador Averell Harriman in Moscow a carved replica of the Great Seal of the United States.  The hollow wooden seal had decorated the wall of four U.S. ambassadors before the listening device it concealed was discovered by the embassy's electronic sweepers in the early 1950s.

"We found it and we didn't know how it worked," [S. Peter] Karlow recalled.  "There was a passive device inside the seal, like a tadpole, with a little tail.  The Soviets had a microwave signal beamed at the embassy that caused the receptors inside the seal to resonate."  A human voice would affect the way the device resonated, allowing the words to be picked up.  "Technically it was a passive device, no current, no batteries, an infinite life expectancy."

The effort to copy the Soviet bug that had been discovered inside the Great Seal was given the code name EASY CHAIR by the CIA.  The actual research was being performed in a laboratory in the Netherlands in two supersecret projects code-named MARK 2 and MARK 3.

Unknown to Karlow and the CIA, British intelligence had succeeded in replicating the Soviet bug, which MI5, the British internal security service, code-named SATYR.  In his book Spycatcher, former MI5 official Peter Wright said he first thought the device was activated at 1,800 megahertz, but then tuned it down to 800 MHz and it worked.  But, according to Karlow, the British did not share their secret with the CIA.

Karlow's work on EASY CHAIR was to have unexpected consequence.  When Anatoly Golitsin dug his package out of the snowbank in front of Frank Friberg's house in Helsinki, one of the papers it contained was a KGB technical document warning that the CIA was working on an eavesdropping system to match the Soviet bug.

Excerpt from The Ultimate Spy Book, by H. Keith Melton

In the early 1950s, a Soviet listening device was found in the American Embassy in Moscow.  This came to the attention of the world when it was displayed at the United Nations by the American ambassador in May, 1960.  It was a cylindrical metal object that had been hidden inside the wooden carving of the Great Seal of the United States -- the emblem on the wall over the ambassador's desk -- which had been presented to him by the Soviets.

The Great Seal features a bald eagle, beneath whose beak the Soviets had drilled holes to allow sound to reach the device.  At first, Western experts were baffled as to how the device, which became known as "The Thing" worked, because it had no batteries or electrical circuits.  Peter Wright of Britain's MI5 discovered the principle by which it operated.  MI5 later produced a copy of the device (codenamed SATYR) for use by both British and American intelligence.


A radio beam was aimed at the antenna from a source outside the building.  A sound that struck the diaphragm caused variations in the amount of space (and the capacitance) between it and the tuning post plaste.  These variations altered the charge on the antenna, creating modulations in the reflected radio beam.  These were picked up and interpreted by the receiver.

Excerpt from a November 14, 2004 TSCM-L mailing list post, by James M. Atkinson of the Granite Island Group.

The audio transmitters you mention can be done by introducing a microphone into the sensor housing, or by taping or suspending a small piece of foil or metalized mylar onto the microwave beam of the sensor.  A good example of this would be a PIR/Microwave sensor that is mounted on the wall of the office of an executive and is directed towards the window with drapes.  The eavesdropper places a very lightweight piece of foil inside of behind the drapes.  The air in the room slightly moves the foil which causes a very slight doppler shift in the 10 GHz signal that can be picked up some distance away from the targeted area.  The critical parts of the equation is that the metallic foil has to be as thin and light as possible (minimal mass), should be in the main beam (easy enough), and should have sharp, almost saw tooth edges around the outside.

Excerpt from Don't Bug Me: The Latest High-Tech Spy Methods , by M. L. Shannon

Besides the microwave frequency bugs from an eariler section, there are other ways to use microwaves for surveillance.  The first method is to concentrate a microwave beam on something that vibrates from the sound in the room in which it is placed.  The reflected beam, coming back, is converted into sound, like the laser devices detailed in the next part.

In the U.S. Embassy in Moscow, the sculpture of the American eagle that the Soviets presented as a gift was made so it would act as a sounding board for reflecting microwaves.  Beware of bears bearing gifts.  In addition, the steel rebars (reinforcement bars) inside the concrete walls were arranged in such a way that they would also reflect the microwave beam, just like the eagle.

The second method, used both outside and inside, is to plant a small device called a resonator, which looks like several quarter-size metal disks with a small rod through the center, inside the area to be bugged.  The resonator may be inside a small metal cylinder.  A microwave transmitter is placed somewhere near the target on one side, and a receiver goes on the other side.  A concentrated beam from the transmitter is directed at the point where the resonator is hidden.

This device is vibrated by sounds in the room in which it is placed and modulates the microwave beam.  When the receiver picks it up, it can demodulate (recover) this sound.  This device is very expensive and therefore very unlikely to be encountered.

Another system that some scientists in Germany are working on will supposedly reflect the microwave beam from the changing density of the air - sound makes tiny compressions in air, and this system is supposed to convert this change in density into sound.

The principle that this works on is probably similar to one that produces laser holograms.  The laser beam is split into two smaller beams.  One of them is bounced off a mirror that changes the phase angle, and when the two beams are recombined, they create an image in space.  Unlike the lasers in the next part, microwaves penetrate walls and don't require a window.  Also, they are unaffected by the things that can interfere with lasers.

Excerpt from Mind Games, by Sharon Weinberger

Concerns about microwaves and mind control date to the 1960s, when the U.S. government discovered that its embassy in Moscow was being bombarded by low-level electromagnetic radiation.  In 1965, according to declassified Defense Department documents, the Pentagon, at the behest of the White House, launched Project PANDORA, top-secret research to explore the behavioral and biological effects of low-level microwaves.  For approximately four years, the Pentagon conducted secret research: zapping monkeys; exposing unwitting sailors to microwave radiation; and conducting a host of other unusual experiments (a sub-project of Project PANDORA was titled Project BIZARRE).  The results were mixed, and the program was plagued by disagreements and scientific squabbles.  The "Moscow signal," as it was called, was eventually attributed to eavesdropping, not mind control, and PANDORA ended in 1970.  And with it, the military's research into so-called non-thermal microwave effects seemed to die out, at least in the unclassified realm.

Excerpt from Mind Control, Playboy Magazine, January 1990.  (PDF)

People in the intelligence community began asking the same questions in the early Sixties when the Soviets were bombarding the U.S. embassy in Moscow with low-intensity microwaves.  No official in Government has ever come up - publicly, at least - with the definitive explanation of what the Soviets were trying to do.  There were three theories.  First was the idea that the K.G.B. was activating its bugs in the embassy.  The second, and most likely, held that they were trying to jam super-secret U.S. listening devices in the embassy that were allowing the National Security Agency to pick up all sorts of secret Kremlin conversations.  The third suggested that the microwaves were somehow meant to affect the brains of the diplomats inside the embassy and alter their behavior.  That is the least likely of the three theories, but it was and is still seriously debated by U.S. scientists pondering the problem.

Excerpt from The Assassination Business: A History of State-Sponsored Murder, by Richard Belfield

The State Department also got in on the act, investigating the bizarre microwave signal being beamed at the U.S. embassy in Moscow.  This TOP SECRET investigation was called Project PANDORA and one of its aims was to see if this was a brain-programming weapon.  But the CIA and the Pentagon were impatient and could not be bothered to wait for the answer so they set up their own deep-black operation called Project BIZARRE, which assumed that the signal was a brainwashing weapon and asked whether they could build a similar one for the USA.

Excerpt from Remote Behavioral Influence Technology, by John J. McMurtrey

The microwave irradiation of the American Embassy in Moscow received little publicity until the winter of 1976 instillation of protective screening, but irradiation was known since 1953.  Original frequencies were 2.56-4.1 GHz with additional intermittent 0.6-9.5 GHz signals being permanent by 1975 in a wide band frequency hopping consistent pattern with one signal pulsating.  The irradiation was directional from nearby buildings and modulated.  Complaint to the Soviets had no avail, but the signals disappeared in January 1979 "reportedly as a result of a fire in one or more of the buildings."

A 9-11 GHz signal recurred in 1988.  Observed frequencies are basically within the microwave hearing spectrum, and pulsation is required.  Psychiatric cases occurred during the exposure period, though no epidemiologic relationship was revealed with fully a quarter of the medical records unavailable, and comparison with other Soviet Bloc posts.  The CIA had Dr. Milton Zaret review medical Soviet microwave literature to determine the purpose of the irradiation.  He concluded the Russians "believed the beam would modify the behavior of the personnel."  In 1976 the post was declared unhealthful and pay raised 20%.

Excerpt from Theremin: Ether Music and Espionage, by Albert Glinsky

The residential nature of Spaso House limited access by Soviet technicians and thwarted attempts to install concealed sureillance devices.  The house and garden were surrounded on three sides by high brick walls, and an iron fence guarded by plainclothes Russian officers blocked the fourth side.  But Lavrently Beria was determined.  An engineer-magician would be required.

In one of his first dragnets in early '39 - just after the ouster of Yezhov - Beria had sanctioned the arrest of an engineer, Lev Sergeyevich Termen.  Nine months later, the same Termen had been delivered from Kolyma to the sanctuary of the Radio Street design bureau.  Beria knew that - after all, the institution of the sharashka was his creation.  After Sverdlovsk, Lev Sergeyevich had been reassigned to a sharashka a Kuchino, near Moscow, a facility for radio electronics and measuring devices.  There he had designed a "radio beacon whose signals helped locate missing submarines, aircraft, or secret cargo smuggled into the enemy's rear."  In the spring of '45, the Spaso House puzzle would be his next assignment.

Beria's demands were intimidating; there could be no wires, no traditional microphones, and the system had to be encased in something that would not call attention to itself.  For Lev Sergeyevich, the stakes were higher than ever.  Beria was no one to disappoint.  He always had his way, and failure for the inventor could mean a return to Kolyma, or worse.  But Lev Sergeyevich forged a working system.  The only remaining quandary was how to penetrate the ambassador's residence.  With his trademark sleight-of-hand, he soon found his answer in the archetype of the Trojan horse.

July 4, 1945.  The annual Independence Day reception at Spaso House was the one event of the year when Averell Harriman threw open the doors to his Russian hosts.  A delegation of Soviet boy scouts (Pioneers) presented the ambassador with a large wooden plaque - the carved relief of the Great Seal of the United States.  It was offered as "a gesture of friendship" and a token of fine Russian woodcarving.  Harriman thanked the scouts and hung the eagle emblem on the wall over his desk.  Lodged inside was the latest incarnation of Lev Sergeyevich's wizardry - a miniature apparatus bearing the hallmarks of his capacitive work from the space-control instrument to the burglar and fire alarm systems.

Set into a long, trenchlike cavity gouged through an inner surface of the hollow plaque was a small metal cylinder, eleven-sixteenths of an inch deep and roughly the diameter of a quarter.  Attached to the cylinder was a nine-inch long protruding antenna tail.  The device was passive - it had no batteries or current, and its lifespan was indefinite.  Its presence went undetected by the routine X-ray screening of all objects entering Spaso House.  The device became active only when an external microwave beam of 330 MHz was directed at its antenna from a neighboring building, causing a metal plate inside the cylinder to resonate as a miniature tuned circuit.  The wood just behind the eagle's beak was thin enough to allow sound waves from human speech in the ambassador's office to filter through to a diaphragm that moved in response to the sounds.  The pattern of the diaphragm's vibrations caused fluctuations in the capacitiance between the diaphragm itself and the plate of the tuned circuit that faced it, causing it to act as a microphone.  This produced corresponding modulations that were registered in the antenna - much like a broadcast transmitter - and reflected out to be picked up as words on a remote receiver.  Lev Sergeyevich was careful to select a bandwidth he knew was not under the control of American security.  With his experience in tuned circuits from his space-control instrument, and devices like the keyboard harmonium, he was the ideal specialist for the job.

Excerpt from New Scientist, August 1, 1974

The vulgar lie detector continues to progress in its erosion of the dignity of man.  The American Civil Liberties Union - and more power to their corporate elbow - has reported to Congressional subcommittee that the Israeli Weizmann Institute has developed a "microwave respiration monitor" which can tell from half a mile away whether a person is telling the truth or not.  It is claimed by the Union that the apparatus is being tested from a hill overlooking the Allenby Bridge to check on the bona fides of Arabs approaching with intention to cross it.  A microwave signal is directed at the stomach of the would-be river crosser is held to reveal whether his abnormal breathing rate indicates that he is lying under interrogation by the military guardians of the bridge.

Excerpt from The Company We Keep: A Husband-and-Wife True-Life Spy Story, by Robert and Dayna Baer

Authors' Note:  The term parabolic mic substitutes for a device that is still classified.

I slide my chair around so Dan has to look at me.  "This is god-damned bureaucratic terrorism.  We don't have cars.  We don't have a place to live, and on top of it I don't have a clue where we're going to put this damn ray gun."

In fact it's not a ray gun.  It's a kind of parabolic microphone that sucks conversations out of the air at a long distance, even through the walls of buildings.  My plan is to find an apartment with a line-of-sight view of the Hizballah safe house, position the mic in the apartment's window so it can't be seen, and wait for the Hizballah operatives to blurt out something they shouldn't - a name, an address, or a telephone number.


It can't be a coincidence, I think.  There's no reason anyone would take a picture of our apartment.  I peek around the curtain for a second look.  He's still there, his camera pointed directly up at our building.  I turn around to look at the parabolic mic.  It's back away from the window, and behind a cloth hanging from the ceiling.  Even if he were level with our window, he couldn't see it.

Excerpt from Dancing with the Devil: Sex, Espionage, and the U.S. Marines, by Rodney Barker

Throughout the Cold War the Soviets had repeatedly demonstrated a bold proclivity toward the use of clandestine listening devices with legendary success.  They had given a hand-carved replica of the Great Seal to U.S. Ambassador Averell Harriman.  This masterpiece of art and ingenuity, constructed with a wireless resonant cavity, was given a place of honor on one of Harriman's walls, where it hung as an invisible witness to U.S. foreign policy in the making, monitoring the ambassador's conversations for several years, until located.  (Later a U.S. diplomat was quoted as saying they went to the middle of Red Square for their private conversations, while in the embassy "they spoke for the mikes.")

In the years since, the KGB had bombarded the embassy with microwaves to pick up the vibrations of voices on the window-panes; it had slipped an elaborate eavesdropping antenna in the embassy's chimney, stolen the embassy's electronic typewriters and rigged them to transmit every letter; and it had sprinkled a powder that was invisible to the human eye but glowed under certain lights as a way of tracing the travels of suspected agents.

Excerpt from The Master of Disguise, by Antonio J. Mendez

But the Tchaikovsky Street embassy was an ideal site for electronic eavesdropping.  Embassy and Agency security officers estimated that the KGB's ubiquitous local employees had seeded the entire building with hard-wire and wireless bugs.  The windows were silently scanned with microwaves that could reproduce the vibration of conversations into usable recordings at the numerous KGB listening posts ringing the embassy.  Between the overtly inquisitive UPDK local employees and the hidden bugs, Americans, from the ambassador to the lowest-ranking Marine security guard, were subject to audio surveillance during every moment they spent in the U.S. Mission, including their apartments.

Excerpt from Murray Associates, 2010

"This device is simple in concept but very complex in construction.  A remote transmitter sends a strong radio frequency signal aimed at the bug, with a directional antenna if possible.  A separate antenna is used to receive the signal which is reflected from the bug -- and everything else around it.  The trick here is to sense the reflectance variations caused by the bug and ignore other variations such as heating systems rattling ducts, etc.  In order to make the bug work, its antenna needed to be resonant near the incoming frequency with its resonant frequency changed by the movement of a diaphragm.  The diaphragm is of course moved by sound pressure.

The standard quarter wave antenna length explanation is probably not correct since the bug antenna did not appear to be connected to anything like a ground plane.  More likely it was a half wavelength at the excitation frequency.  To make all of this work, the resonant cavity under the diaphragm and bug antenna had to be carefully matched.  Diaphragm position had to be close to the the post for good sensitivity but not so close that it would touch the post as components aged.

One last problem in the operation was the excitation signal.  It didn't take a genius to discover the transmitted signal and subsequently the reflected signal.  It would be important in operation of the bugging system to turn it off when a sweep team was seen in the area.  The rumor is that this device was detected as the sweep technician dialed his receiver past the excitation frequency and heard voices.

This sort of bugs is not likely to be found in corporate or residential eavesdropping situations.  Lax access control, easily installed computer keystroke recorders, high tech baby monitors and cordless phones that broadcast conversations make the work of a modern day Theremin unnecessary."

"The Thing" Block Diagram

From H. Keith Melton's CIA Special Weapons & Equipment


This is how I believe "The Thing" works.  It doesn't follow the description from Peter Wright exactly, but his book does contain numerous (intentional?) technical errors.  Spycatcher was ghostwritten by Paul Greengrass, and these could just be typographical errors.

Update:  Lev Termen's Great Seal Bug Analyzed  by Graham Brooker and Jairo Gomez  (3.6M PDF)

From Electronic Design, Volume 14, Issues 14-17, by S. David Pursglove:

The diaphragm was 3 mils thick that covered the can opening.  The can measured 11/16-inch long, with an inside diameter of 0.775-inch.  The cavity inductance was 1/100 microhenry.  The entire unit, including the 9-inch antenna, weighed 1.1 ounces.  Silver-plated, high-Q resonant cavity.  330 MHz signal outside embassy in van to excite cavity.  Another van with an antenna aim at the cavity tune in on modulated signal.


A Continuous Wave (CW) RF carrier of around 800 MHz is transmitted to the cavity bug via a highly directional parabolic antenna.  This RF carrier needs to be extremely clean, with all the harmonics and spurs surpressed 80+ dBc.

The 800 MHz RF carrier enters the cavity via the 1/4-wavelength antenna probe (9.375 cm, in this case).  The high-Q, silver plated cavity is "tuned" via the adjustable "mushroom" (a 1/4-wavelength shorted stub) to parallel-resonante at an odd-harmonic frequency (3 times higher or 2400 MHz) than the transmitted RF carrier.  The use of higher frequencies will allow for a physically smaller cavity.  Also, a RF carrier which is 3 times higher can share an antenna which is for a frequency 3 times lower, due to the way the current is distributed in the antenna - or at least that's what I think.

But in this resonant cavity, one of the cavity's ends is replaced with a thin metal diaphragm.  The diaphragm may be made from metallized mylar, very thin copper sheet, or even gold leaf.  When sound waves hit this diaphragm, the cavity's resonant frequency will change ever so slightly.  This audio signal then frequency modulates the new, higher frequency return signal.

3456 MHz Resonant Cavity Band Pass Filter

This is an example of a resonant cavity Band Pass Filter (BPF) using copper pipe end-caps and brass tuning screws.  Try replacing the PC board with a metal diaphragm, taking the RF output, as a 1/4-wave (6.5 cm) whip antenna, from a side wall, flooding it with a 1150 MHz CW RF carrier and monitoring 3450 MHz.  It might work.


Cavity Schematic

Experimental starting schematic for a homebrew Resonant Cavity Bug.  I don't have the proper test equipment or a machine shop to verify if it works, but it can be used as a starting block.

The output impedance, Zo, of this cavity is near the standard 50 ohms.  It is based on the following equation:

D1 = Cavity Diameter Outside
D2 = Cavity Diameter Inside (stub)
Zo = Characteristic (or surge) Impedance in ohms

Zo = 138 * log10 (D1 / D2)

Zo = 138 * 1og10 (0.875 / 0.375)

Zo = 50.78 ohms

To be effective, the tuning disc or slug must be placed near a high-voltage point (quarter-wavelength point) along the cavity.

A loose coupling (greater than or equal to 0.10") will have a higher insertion loss, but sharper bandpass (resonance).  Tighter coupling (approx. 0.05") will have a lower insertion loss, but wider bandpass.

In theory, to tune this device, you'll need to connect it to a RF signal generator operating at the frequency you wish to receive then adjust the cavity's tuning screw.  An example is next.  The '?'s mean that I have no idea if this is the correct procedure.

Set a RF signal generator to output a low power (100 mW?) RF signal at 2700 MHz with a FM modulation tone of 1000 Hz and 3000 Hz deviation?.  Connect this to the cavity's SMA antenna jack.  Adjust the Fine Tune screw until the cavity starts to 'howl.'?  That is, when the cavity reaches the proper resonant frequency (2700 MHz) the diaphragm should turn into a speaker, and you'll hear the modulating 1000 Hz audio tone.  Or at least I think so.

To use the bug, illuminate the cavity with a very strong & clean 900 MHz? CW RF carrier and receive the "resonanated" FM audio at 2700 MHz.  I think that might work.  Otherwise, illuminate it with a very strong & clean 2700 MHz CW RF carrier and try to recover the audio as a doppler shift (mix the outgoing frequency with the incoming frequency in a diode mixer?).

Since the cavity's antenna jack is at 50 ohms, standard antennas can be used for easier testing.


Paper Thin Bug?

A highly experimental idea is to use a Piezo speaker as a microphone and variable capacitance.  Combined with a small surface-mount inductor/capacitor tuned network and antenna, a theoretically "paper thin" bug is produced.

There are, however, numerous "bugs" to work out with this type of design though.  Piezo speakers have a fairly high capacitance (the one in the picture measured 0.067 µF @ 300 kHz).  When used in a passive-tuned circuit, this will result it a very low illuminating frequency.



Imagine using a circuit trace repair pen to "draw" the inductive and antenna elements.  This type of "bug" would be as thin as paper.


Scenes from the movie The Recruit.

Updates & Experiments

Further experimentation with homebrew microwave interferometer surveillance devices is proving to be very successful.  Microwave interferometers work by emitting an RF carrier and mixing the reflected (returned) signal with the initial RF carrier.  The Intermediate Frequency (IF) output is the difference in phase of the two signals.  If the reflector surface (say, a filing cabinet) is modulated by nearby audio, the returned RF carrier will also be modulated with that audio.  While the concept may sound complicated, most of the hardware you need (for experimenting) is found inside an automatic door opener.

Everyday automatic door openers utilize a 10 GHz "Gunnplexer" to generate this Doppler effect, which is used to detect the approaching people.  The IF output is a low frequency sine wave which is further amplified and rectified to control the door opening relay.



The beauty in using a microwave interferometer for surveillance work is the fact there is no need to plant any type of resonant cavity device.  Everyday objects can become the "resonator."  Peter Wright's Spycatcher also mentions MI5 used to develop specially-shaped everyday common objects like ashtrays, sculptures, ornaments, etc. to become resonators.  This enhanced the strength and audio quality of the reflected signal.

With the onslaught of vehicle radar systems, easily obtainable Gunn oscillators operating at around 77 GHz are becoming available.  At this high of frequency, and with a good parabolic dish, the RF beamwidth will be very narrow.  This makes receiving doppler audio reflections off individual objects - or even directly from a person's larynx - possible.

Sample Audio

This is an audio capture from a GBPPR Interferometric Surveillance Device aimed at a human larynx.

The words spoken are "Testing Testing 1 2 3" and the range was measured in inches.

Here is little information pamphlet on a similar commerical surveillance device called the 'Sabre' that uses remote RF energy (888 MHz) to 'illuminate' a remote transponder (125 kHz) which contains the target audio.  It is made by Security Research (Audiotel) in the U.K.

Here are some good millimeter wave RF application notes from QuinStar Technology.  Be sure to "read between the lines."    ;)

And here is something you don't see everyday...  A patent application explaining everything in exquisite detail:

This version appears to use a microwave interferometer consisting of a HP Model 83723B generating a synthesized 20 GHz RF signal source which then drives a HP Model 8349B 20 GHz RF amplifier.  This boosts the final RF output signal to around +20 dBm (100 mW).  The 20 GHz RF signal is also initially modulated with a 1 kHz sine wave using a HP Model 33120A audio signal generator.  The final modulated and amplified RF signal is then feed through a HP Model P752C-10 10 dB directional coupler to the Narda 639 waveguide 18 dB horn antenna.  The weak received (reflected) 20 GHz signal is then amplified approx. 14 dB using a MITEQ Model AMF-3D-000118000-33-10P low-noise amplifier.  This is then downconverted to a 1 GHz IF using a MITEQ Model SBE0440LW1 2nd harmonic mixer and a HP Model 8340A synthesized RF signal source to provides the mixer's local oscillator input.  The mixer's new IF output is amplified approx. 30 dB using a MITEQ Model 4D-00011800-33-10P RF amplifier and bandpass filtered using a 300 MHz wide Reactel Model 381-1390-50S11 filter.

A HP Model 8473C low-barrier Schottky diode detector demodulates the 1 GHz IF signal, recovering the final audio intelligence output.  The initial 1 kHz modulation tone allows a "lock-in amplifier" to be used during the final audio demodulation stage.  A lock-in amplifier, a Stanford Research Model SR830 in this case, tracks the phase of the input 1 kHz modulation tone and attempts to extract that same tone in the received audio.  This allows one to extract audio intelligence from any interfering noise.  The received 20 GHz signal would contain both amplitude and phase variations which contain the required target intelligence.  The Analog Devices AD630 datasheet contains an example lock-in amplifier schematic and sample oscilloscope photos.

Here is a fantastic email post by James M. Atkinson on the TSCM-L mailing list which describes operating similar devices in several real-world scenarios.  (Additional Info)

Here is our (fairly simple) homebrew lock-in amplifier project based around the Analog Devices AD630.

A laser version of the above type of surveillance device is described in this U.S patent application:

"A system for remotely detecting vocalizations of speech comprising: means for vibrating in response to the vocalizations of speech, said responsive vibrating means capable of being located on a throat region of a speaking person and capable of being reflective of impinging radiation; means for transmitting the radiation onto said responsive vibrating means and receiving the radiation from said responsive vibrating means, said transmitting and receiving radiation means capable of generating voltage output signals representative of the vocalizations; and means coupled to receive the voltage output signals from said transmitting and receiving radiation means for reproducing and transmitting the speech of the vocalizations from the output voltage signals."

Here are some audio extracts from an older model Decatur MV-715 Range Master X-band police radar configured to record the audio ouput straight from the speaker.

For further experimenting on using a Decatur Range Master radar to remotely intercept telephone audio, refer to this project:

Internal photos of a Decatur MV-715 & MV-724 radar gun.

Notes / Links / Datasheets

  1. The Great Seal Bug Story  by Kevin D. Murray of Murray Associates.  Lots of very good technical details and first-hand operational accounts.
  2. The Great Seal Bug  How does it work?  (700k PDF)
  3. A Trojan Seal  by Ken Stanley, who served as the chief technology officer at the State Department's Diplomatic Security Service from 2006 to 2008.
  4. Fascinating Profile of the Soviet KGB's Little-Known Tech Wizard
  5. The Thing  Caution: Wikipedia
  6. Peter Wright  Caution: Wikipedia
  7. Spycatcher  Caution: Wikipedia
  8. Introduction to "Embassy Moscow: Attitudes and Errors"  by Henry J. Hyde
  9. The Microwave Furor  Last month the U.S. confirmed that for some 15 years the Soviet Union has been beaming microwaves at the hulking nine-story U.S. embassy on Moscow's Tchaikovsky Street.
  10. Russia Used Microwave  by Jack Anderson, Boca Raton News, May 9, 1972.
  11. Cool-Amp Silver Plating Powder  Rub on silver plating.
  12. Microwave Filter Design  (Page 2)  (Page 3)
  13. A Simple Cavity Filter for 2304 MHz
  14. 904 MHz & 1265 MHz Copper Pipe Filters
  15. 47 GHz Equipment and Techniques
  16. Pcom 23 GHz Conversion Info
  17. Cavity Coupling  (Page 2)
  18. Online Metals  Sells the copper foil, plate, rod, and tubing.
  19. Caig CircuitWriter Precision Conductive Ink Dispenser
  20. Leon Sergeivitch Termen - The Thing
  21. M/A-Com MA-87728 Series 10 GHz Gunnplexer  (150k PDF)
  22. M/A-Com MA-87127 Series 10 GHz Gunnplexer  (1M PDF)
  23. M/A-Com Gunn Diodes  Brief overview of the most common models.
  24. M/A-Com MA49138-111 Gunn Diode Diagram  111-style package.  250 mW RF output at +10 VDC / 900 mA.  Similar to the MDT MG1007-15.
  25. M/A-Com MA49000-Series Gunn Diode Information  (Page 2)  (Page 3)
  26. M/A-Com MA40181 Mixer Diode Information  Common K-band mixer diode.
  27. Short Description of Gunnplexer Conversion for 10 GHz Amateur Radio Use  Includes notes on how to test Gunn diodes.
  28. Microsemi 10 & 24 GHz Gunnplexer Information  (260k PDF)
  29. Gunnplexer Application Notes
  30. Microsemi Gunn Diodes Overview & Data  (220k PDF)
  31. Microsemi Gunn Diode Application Notes  (144k PDF)
  32. Fundamentals of Commercial Doppler Systems  Speed, motion, and distance measurements techniques.  (174k PDF)
  33. Microsemi Gunn Diodes  (209k PDF)
  34. Infineon Microwave Motion Sensor KMY 24  (50k PDF)  (Application Note)
  35. Guardian Alert: How it Works  10 GHz backup collision warning system.
  36. Tellurometer  Microwave electronic distance measurement equipment.  These are a good source for high-power 10 or 35 GHz transmitters with integrated receivers.  (Picture of a Tellurometer)
  37. General Electric GEMLINK Information  Overview of a General Electric GEMLINK K-band video transmitter.
  38. Microwave Interferometers for Non-Contact Vibration Measurements on Large Structures  (338k PDF)
  39. Microwave Interferometry to Elucidate Shock Properties  (324k PDF)
  40. A Microwave Interferometer to Measure Particle and Shock Velocities Simultaneously  (223k PDF)
  41. "A Gunn diode (diodes with ranges of power 10 to 100 mW have been used) operating at 10.515 GHz supplies the microwave power.  The 3-db coupler divides the microwaves into a detector signal and a local oscillator signal.  The local oscillator power is directed to the mixer diodes.  The electrical distance between the mixer diodes is adjusted so that the signals obtained are in quadrature.  This feature is useful but not at all necessary.  A single mixer diode would suffice.  The circulator directs the signal reflected from the detector cavity to the arm containing the mixer diodes but in the other direction.  In the mixer arm, therefore, we have two counter-propagating 10 GHz signals whose phase difference depends upon the change in the time delay in the detector cavity.  This time delay consists of two parts: first, the time that would be required for the microwaves to traverse the distance to the reflecting surface and back in a vacuum and, second, the additional delay due to the index of refraction of the material in the cavity."

  42. X-Band Waveguide Circuits: Doppler Radar and Interferometer  (889k PDF)
  43. Design of 90 GHz Band Radiometer System for Remote Sensing Applications  (165k PDF)
  44. New Device Will Sense Through Concrete Walls  Radar Scope press release.
  45. Through Wall Sensing of Human Breathing and Heart Beating by Monochromatic Radar  IEEE login required.
  46. Noise Considerations for Remote Detection of Life Signs with Microwave Doppler Radar  IEEE login required.
  47. Microwave System for the Detection of Trapped Human Beings  IEEE login required.
  48. Microwave Human Vocal Vibration Signal Detection Based on Doppler Radar Technology  IEEE login required.
  49. An UWB Radar-Based Stealthy 'Lie Detector'  (530k PDF)
  50. Development of a Novel Contactless Mechanocardiograph Device  (1.0M PDF)
  51. Multi-Frequency Sensor for Remote Measurement of and Heartbeat  (3.5M PDF)
  52. Detection of Multiple Heartbeats Using Doppler Radar  (114k PDF)
  53. Remote Medical Diagnosis  CIA's monitoring the health of very important patients.  (1.2M PDF)
  54. Life Assesment Dectector System (LADS)  A microwave Doppler movement measuring device, can detect human body surface motion, including heartbeat and respiration, at ranges up to 135 feet.  ( Mirror)
  55. Feasibility Study for Non-Contact Heartbeat Detection at 2.4 GHz and 60 GHz  (233k PDF)
  56. Kuhne Electronic  High-quality microwave amplifiers and transverters.
  57. QuinStar Microwave/Millimeter Wave RF Components
  58. Doppler Sensor Heads  WiseWave Tech Bulletin No. SRF  (836k PDF)
  59. Development of Inexpensive Radar Flashlight for Law Enforcement and Corrections Applications  (882k PDF)
  60. Information on Peter Wright
  61. Book Review of Peter Wright's Spycatcher
  62. Spooks' Corner: Listening to Typing, Spycatcher, and Talking to Tolkachev  UCB researchers attempt at MI5's "ENGULF" techniques and other Cold War stories.
  63. Acoustic Cryptanalysis  Determine computer machine code via its electromagnetic emanations.
  64. Slashdot: Snooping Through Walls with Microwaves  Note:  Slashdot posters are the quite easily the dumbest people on the planet.
  65. Eavesdropping Through a Wall
  66. An Overview of Microwave Sensor Technology  by Jiri Polivka  (245k PDF)
  67. Cops Have Eyes on X-Ray Vision
  68. Radar Flashlight for Through-the-Wall Detection of Humans  (Press Release)
  69. Radar Sensing of Heartbeat and Respiration at a Distance with Security Applications  SPIE login required.  (If anyone with SPIE access can send me a copy of this paper, it would be much appreciated!)
  70. Microradar Microphone
  71. "The nonacoustic microradar microphone detects breathing sounds in the chest, which cannot be heard by a conventional stethoscope.  It also robustly detects vocal cord motion when held over the Adam's apple.  Since the microradar 'stethoscope' is immune to external noises, it is particularly useful in an ambulance or helicopter, or on the battlefield."

  72. Micropower Impulse Radar  (1.1M PDF)  (Overview)  (FAQ)  (Patents)
  73. Micropower Impulse Radar Technology and Applications  UCRL-ID-130474  (2.9M PDF)
  74. Prediction of Buried Mine-Like Target Radar Signatures Using Wideband Electromagnetic Modeling  UCRL-JC-130338  (969k PDF)
  75. Imaging Radar for Bridge Deck Inspection
  76. Radar Imaging for Combatting Terrorism  (775k PDF)
  77. Through-the-Wall Surveillance Technologies  (97k PDF)
  78. An Acousto-Electromagnetic Sensor for Locating Land Mines
  79. USENET Posting - 1  Information from "Gharlane of Eddore"
  80. Microwave Listener System  USENET info request.  (Thread)
  81. Homebrew Microwave Interferometer  USENET info request.
  82. Well if you wanted a slick chance you would:
    A) modulate the carrier to chop the audio up to higher frequency
    B) recover the phase, using a low sideband noise oscillator
    c) demodulate the phase carrier to extract the 1/1000 p1/2 phase modulation
    that you can expect to see with a 1 uM vibration. 
    - Marc H. Popek
  83. Radar Microphone?  USENET info request.
  84. Non-Contact Detection of Breathing Using a Microwave Sensor  (311k PDF)  (Abstract)
  85. Contact-Free Measurement of Heart Rate Variability via a Microwave Sensor  (549k PDF)  (Abstract)
  86. Blind Separation of Human Heartbeats and Respiration by the Use of a Doppler Radar Remote Sensing  (103k PDF)
  87. Less Contact: Heart Rate Detection Without Even Touching the User  (742k PDF)
  88. A Non-Contact Vital Sign Monitoring System for Ambulances Using Dual-Frequency Microwave Radars  (473k PDF)  (Additional Info)
  89. Signal Processing Methods for Doppler Radar Heart Rate Monitoring  (1.0M PDF)
  90. Doppler Radar Sensing of Multiple Subjects in Single and Multiple Antenna Systems  (255k PDF)
  91. Multi-Target Estimation of Heart and Respiration Rates Using Ultra-Wideband Sensors  (153k PDF)
  92. Microwave Frequencies Used to Help Detect Victims "Buried Alive"  by Mark-Alan Lim  (250k PDF)
  93. An Example of Gear for the 145 GHz Amateur Band
  94. An Introduction to 24 GHz  by Steve Kavanagh, VE3SMA
  95. My Activities on 24 GHz  by Dave, VK2TDN
  96. Low-Noise Block Downconverter X-Band Mods  Model NJR2117FK, by N6CA  (Additional Info)
  97. Frequency West Brick Oscillator Info
  98. Eudyna FMM5061VF X-Band Power Amplifier  9.5-13.3 GHz, 27 dBG, Pout +33 dBm.  Sold by Down East Microwave.  (180k PDF)
  99. A 600 GHz Imaging Radar for Contraband Detection  (450k PDF)
  100. Radar Detector to Microwave Receeiver Conversion  by Steve J. Noli, WA6EJO.  73 Magazine, February 1991.  (499k PDF)
  101. The Challenge of 10.5 GHz  by Stirling Olberg, W1SNN.  73 Magazine, April 1978.  (1.5M PDF)
  102. 10 GHz Gunnplexer Transceivers - Construction and Practice  by James R. Fisk, W1HR.  Ham Radio, January 1979.  (1.5M PDF)
  103. Gunn Oscillator Design  by Richard Bitzer, WB2ZKW.  Ham Radio, September 1980.  (893k PDF)
  104. Frequency Measurement with the Interferometer  by Bill Hoisington, K1CLL.  73 Magazine, September 1972.  (Page 2)
  105. A Synchronous Detector for A.M. Transmissions  (485k PDF)
  106. Balanced Modulator/Demodulator Applications Using the MC1496/1596  Philips Semiconductor AN189.  Includes a phase detection circuit.  (70k PDF)
  107. The Gunnplexer Cookbook  A microwave primer for radio amateurs and electronics students.  by Robert M. Richardson, W4UCH.  (12.7M PDF)
  108. The 10 GHz Cookbook  by John C. Roos, K6IQL.  (4.6M PDF)
  109. 'Cone of Silence' Keeps Conversations Secret
  110. Heartbeat Radar
  111. Decatur Genesis-VP Handheld Radar  User Manual  (2.2M PDF)
  112. Stalker Radar - Raw Manual Directory
  113. Union Switch & Signal DR-50 Solid State Radar Unit  10 GHz Doppler radar unit which includes a detailed schematic.  (939k PDF)
  114. STU-III Key Leakage via Blackberry RF Illumination
  115. Eavesdropping Using Microwaves  by Henry Davis  (Addendum)
  116. A Radiating Cable Intrusion Detection System  by Spencer J. Rochefort, Raimundas Sukys, and Norman C. Poirier  (3M PDF)  (Abstract)
  117. Development and Testing of a Multiple Frequency Continuous Wave Radar for Target Detection and Classification  (3.8M PDF)
  118. A Simple Strategy for Life Signs Detection via an X-Band Experimental Set-Up  (423k PDF)
  119. Beam, Development for Battlefield, Detects Onset of Heart Attacks  The New York Times, July 7, 1987.
  120. Development of an EM-Based Lifeform Detector  (4.8M PDF)  (First Version)
  121. Wireless Bio-Radar Sensor for Heartbeat and Respiration Detection  (1.0M PDF)
  122. Doppler Radar Architectures and Signal Processing for Heart Rate Extraction  (387k PDF)
  123. Wireless Crib Monitor Keeps Tabs on Baby's Breathing  (Video)
  124. Physical Examination of the DKL LifeGuard Model 3  Scam "heartbeat" detector reviewed by Sandia National Labs.  A total hoot to read...  (2.2M PDF)
  125. Detection of Human Breathing and Heartbeat by Remote Radar  (PDF)
  126. Through Wall Detection and Recognition of Human Beings using Noise Radar Sensors  (292k PDF)
  127. Gated UWB FMCW/SF Radar for Ground Penetration and Through the Wall Applications  (1M PDF)
  128. Remote Sensing of Body Signs and Signatures  (3.2M PDF)
  129. Application of a Continuous Wave Radar for Human Gait Recognition  (368k PDF)
  130. Chemring RE80M2EST Electronic Stethoscope  "The RE80M2EST also features an optional Microwave Doppler Contactless Microphone which can be positioned with a useful stand off from the device being monitored.  The Contactless Microphone can read the signature of a range of mechanical and electronic timers.  It can be used as an autonomous, hand held search instrument or be patched in to the main Stethoscope for remote monitoring."  (Datasheet)
  131. Retrodirective Noise-Correlating Radar in X-Band  (927k PDF)
  132. Life Detector  Popular Science, August 1989
  133. Quadrature Demodulation with DC Cancellation for a Doppler Radar Motion Detector  (301k PDF)
  134. Non-Contact Detection and Monitoring of Human Cardiopulmonary Activity  (670k PDF)
  135. Non-Contact Vital Sign Detection System
  136. A New Method for Identifying the Life Parameters via Radar  (1.4M PDF)
  137. Design and Construction of a Blood Flow Dectector Probe for Medical Applications  Acoustical Imaging, Volume 27.  (982k PDF)
  138. Doppler Flow Measurements  (724k PDF)
  139. Doppler Technology  Cerebrovascular Ultrasound: Theory, Practice and Future Developments  (1.1M PDF)
  140. Ultrasound in Medical Diagnostic Instrumentation  A Textbook of Medical Instruments  (1.4M PDF)
  141. Microwave Short-Range Interferometric Radar  (290k PDF)
  142. Direct-Reading Type Microwave Interferometer  (626k PDF)
  143. Multitunable Microwave System for Touchless Heartbeat Detection and Heart Rate Variability Extraction  (1.5M PDF)
  144. Heart Rate Measurement  International Patent PCT/IB2006/054524  (1.6M PDF)
  145. Microwave Gesture Sensing  A doppler radar based gesture measurement system capable of delivering positional information.  (Additional Info & Schematics)
  146. A Novel Radar Sensor for the Non-Contact Detection of Speech Signals  (237k PDF)  (Original)
  147. Low-Cost Differential Front-End for Doppler Radar Vital Sign Monitoring  (662k PDF)
  148. LifeMonitor  (559k PDF)
  149. Contact-less Assessment of In-Vivo Body Signals Using Microwave Doppler Radar  (782k PDF)
  150. A Viewpoint of Time Variant Dielectric EŽect in Vital Sign Detection Using Microwave Radar  (620k PDF)
  151. A Robust Voice Activity Detector Using an Acoustic Doppler Radar  (1.1M PDF)
  152. Use of Low-Power EM Radar Sensors for Speech Articulator Measurements  (234k PDF)
  153. Doppler Measurement  (1.7M PDF)
  154. Make Your Own TSA 'Naked' Scanner  by Jeri Ellsworth
  155. A Compact Low-Cost Add-On Module for Doppler Radar Sensing of Vital Signs Using a Wireless Communications Terminal
  156. Medical Radar Literature Overview  (98k PDF)
  157. Detection of Objects Buried in Wet Snowpack by an FM-CW Radar  (546k PDF)
  158. Human Body Detection in Wet Snowpack by an FM-CW Radar  (346k PDF)
  159. Synthetic Aperture FM-CW Radar Applied to the Detection of Objects Buried in Snowpack  (785k PDF)
  160. Micro-Doppler Radar Signatures for Intelligent Target Recognition  (1.8M PDF)
  161. Radar Vibrometry: Investigating the Potential of RF Microwaves to Measure Vibrations  (280k PDF)
  162. Remote Sensing of Heart Rate and Patterns of Respiration on a Stationary Subject Using 94 GHz Millimeter-Wave Interferometry  (1M PDF)
  163. UHF Measurement of Breathing and Heartbeat at a Distance  IEEE login required.
  164. Micro-Doppler Effect in Radar: Phenomenon, Model, and Simulation Study  (640k PDF)
  165. Microwave Interferometer for Non-Destructive Testing  (650k PDF)
  166. Microwave Interferometer and Reflectometer Techniques for Thermonuclear Plasmas  (3.5M PDF)
  167. Microwave Interferometry (90 GHz) for Hall Thruster Plume Density Characterization  (112k PDF)
  168. Using a Microwave Interferometer to Measure Plasma Density  (569k PDF)
  169. Microwave Short-Range Interferometric Radar  (455k PDF)
  170. X-Band Microwave Interferometer for Study of Hypersonic Turbulent Wake on Range 5  (2.0M PDF)
  171. Testing a Very Good Microwave Interferometer  by Nils Brenning  (438k PDF)
  172. Instrument Reflections and Scene Amplitude Modulation in a Polychromatic Microwave Quadrature Interferometer  (996k PDF)
  173. Microwave Interferometric Measurements of Particle and Wave Velocities in Porous Media  (2.8M PDF)
  174. Optimization of a Portable Microwave Interference Scanning System for Non-Destructive Testing of Multi-Layered Dielectric Materials  (608k PDF)
  175. K-Band Single Channel Interferometer  (30k PDF)
  176. Microwave Interferometer 94 GHz Solid-State Sources  (190k PDF)
  177. A 90 GHz Phase-Bridge Interferometer for Plasma Density Measurements in the Near Field of a Hall Thruster  (689k PDF)
  178. Development of Millimeter Wave Integrated-Circuit Interferometric Sensors for Industrial Sensing Applications  by Seoktae Kim  (1.4M PDF)
  179. Theory, Analysis and Design of RF Interometric Sensors  by Seoktae Kim and Cam Nguyen  (8.9M PDF)
  180. Microwave Based Civil Structure Inspection Device  (906k PDF)
  181. Microwave Inspection of Civil Structures  (326k PDF)
  182. Time-Frequency Analysis of Terahertz Radar Signals for Rapid Heart and Breath Rate Detection  (2.0M PDF)
  183. A Surface Vibration Electromagnetic Speech Sensor  (400k PDF)
  184. Radar Information from the Partial Derivatives of the Echo Signal Phase from a Point Scatterer  (3.2M PDF)
  185. Radar Technology For Acquiring Biological Signals  (563k PDF)

Glottal Electromagnetic Micropower Sensors

Additional notes and links.

  1. The Physiological Basis of Glottal Electromagnetic Micropower Sensors (GEMS) and Their Use in Defining an Excitation Function for the Human Vocal Tract  by Gregory Burnett
  2. Denoising of Human Speech Using Combined Acoustic and EM Sensor Signal Processing  (1M PDF)
  3. An Assessment of Speech Related Information Contained in GEMS Signals  (500k PDF)
  4. Human Speech Articulator Measurements Using Low Power, 2 GHz Homodyne Sensors  (500k PDF)
  5. Measuring Glottal Activity During Voiced Speech Using a Tuned Electromagnetic Resonating Collar Sensor  (454k PDF)
  6. EM Wave Measurements of Glottal Structure Dynamics  (1.1M PDF)
  7. Multimodal Speaker Authentication Using Nonacoustic Sensors  (100k PDF)
  8. A Novel Non-Acoustic Voiced Speech Sensor: Experimental Results and Characterization  by Kevin Keenaghan  (1M PDF)
  9. A Surface Vibration Electromagnetic Speech Sensor  (400k PDF)
  10. Sensing of Living Casualties on the Modern Integrated Battlefield  (2.4M PDF)
  11. Micropower Electro-Magnetic Sensors for Speech Characterization, Recognition, Verification, and Other Applications  (428k PDF)
  12. Micropower Electro-Magnetic Sensors for Speech Characterization: Recognition, Verification, and Other Applications  Presented at the 1998 International Conference on Spoken Language Processing.  (1.8M PDF)  (1999 Paper)
  13. Noise Robust Digit Recognition Using a Glottal Radar Sensor for Voicing Detection  (121k PDF)
  14. Speaker Verification Using Combined Acoustic and EM Sensor Signal Processing  (634k PDF)
  15. EM Sensor Measurements of Glottal Structure Versus Time  (2.1M PDF)
  16. Low-Bandwidth Vocoding Using EM Sensor and Acoustic Signal Processing  (135k PDF)
  17. Measurements of Glottal Structure Dynamics  (2.1M PDF)
  18. Aliph General Electromagnetic Movement Sensor User Manual  Revision B, Version 1.  (1.1M PDF)
  19. Aliph RadioVibrometer User Manual  Revision B, Version 3.  (840k PDF)
  20. Aliph RadioVibrometer User Manual  Revision C, Version 2.  (804k PDF)
  21. Theory and Use of the Aliph RadioVibrometer  Version 1.3.  (1.1M PDF)
  22. Improved Near-Field ARV (GEMS) Neck Interface  (137k PDF)

Related Books

Special Topics in Electromagnetics

(Excerpt from Chapter 4 - Biological Applications of Electromagnetic Waves)

  1. Page 117
  2. Page 118  Microwave Life-Detection Systems
  3. Page 119
  4. Page 120
  5. Page 121
  6. Page 122
  7. Page 123  A X-Band Microwave Life-Detection System
  8. Page 124  Block Diagram
  9. Page 125
  10. Page 126
  11. Page 127
  12. Page 128
  13. Page 129
  14. Rest of this Chapter  Missing pages: 137, 149, and 156.  (4.3M PDF)
  15. Automatic Clutter-Canceler for Microwave Life-Detection Systems  (322k PDF)
  16. An X-Band Microwave Life-Detection System  Original IEEE paper.  If anyone with IEEE access can send me a copy of this paper, it would be much appreciated!

Related Patents

  1. Ultra-High Frequency Modulator  U.S. Patent 2,238,117
  2. Apparatus and Method for Remotely Monitoring and Altering Brain Waves  U.S. Patent 3,951,134
  3. FM/CW Surveillance Radar System with Range Gating  U.S. Patent 3,932,871
  4. Microwave Image Converter  U.S. Patent 4,280,055
  5. Microwave Interferometer  U.S. Patent 4,359,683
  6. Device and Method for Detecting Localization, Monitoring, and Identification of Living Organisms in Structures  U.S. Patent 7,057,516
  7. Doppler Radar Receiver  U.S. Patent 3,896,436
  8. Short Pulse/Stepped Frequency Radar System  U.S. Patent 2005/0270219  (Radar Scope)
  9. Non-Contact Measurement System for Accurate Measurement of Frequency and Amplitude of Mechanical Vibration
  10. Non-Contact Vital Signs Monitor  U.S. Patent 4,958,638  (Additional Info)
  11. "The VSM radar system is a straightforward homodyne receiver.  It operates using frequency modulated continuous wave (FM-CW) transmission, which allows for very low power levels.  The safe human power density exposure level at its operating frequency of 35 GHz is 10 mW/cm2.  A simple approximation using uniform distribution and an antenna aperture of 2 cm by 3 cm gives a power density at the antenna face of 0.017 mW/cm2, nearly a factor of 1000 below the safe level.

    When the VSM's antenna is trained on the chest wall of a subject, the VSM is capable of measuring and distinguishing minute movements resulting from the mechanical activity of the heart and lungs.  As the subject's chest wall moves, the exact phase of the return signal changes.  To avoid the possibility of phase-related dead spots, two signals differing in phase by 90 degrees are used to demodulate the signal to baseband (DC).  The two resulting 'time-varying DC' signals represent the sine and cosine of a phase angle corresponding to the changing position of the target, in this case the motion of the chest wall.  The current VSM operates at a frequency of 35 GHz with a corresponding wavelength of only 8.6 mm.  This provides a response sensitive enough to detect the small motions caused by cardiac function."

  12. Apparatus and Method for Monitoring the Waveform of Cyclic Movement Within the Thorax of an Individual  U.S. Patent 4,967,751
  13. Vibration Detection  U.S. Patent 5,828,331  (Medcon Limited)
  14. Detection of Vibrating Target Signatures  U.S. Patent 4,673,940
  15. Traffic Radar and Apparatus Therefor  U.S. Patent 4,020,490  (Partial Decatur Police Radar Schematic)
  16. Method and Apparatus for Digitally Determining the Speed of a Moving Object  U.S. Patent 3,689,921  (Partial Kustom Signals Police Radar Schematic)
  17. Movement Detector for Detecting the Movement of a Breathing Activity  WIPO WO/2009/083017  (1.5M PDF)
  18. Radar System for Remotely Measuring a Subject's Heartrate  WIPO WO/2007/063516  (1.3M PDF)
  19. Non-Contact Physiologic Motion Sensors and Methods for Use  U.S. Patent Application 2010/0152600
  20. Determining Presence and/or Physiological Motion of One or More Subjects with Multiple Receiver Doppler Radar Systems  U.S. Patent Application 2008/0077015  (685k PDF)
  21. Arrangement and Method for Obtaining Information Using Phase Difference of Modulated Illumination
  22. Detection of Vibrating Target Signatures  U.S. Patent 4,673,940
  23. Modulated Pulse Doppler Sensor  U.S. Patent 6,426,716
  24. Phase-Based Sensing System  U.S. Patent 6,489,917

Related Audio / Video

  1. The Spying Game: "Walls Have Ears"  Part 1  (YouTube)

  3. CIA Laser Listener  (YouTube)
  4. 1960 U.N. Spy Debate  (YouTube)
  5. GBPPR Vision #25: Overview of the NSA's CTX4000/PHOTOANGLO Radar Units  General overview of the NSA's CTX4000/PHOTOANGLO illumination radars for remote technical surveillance applications.  (YouTube)
  6. GBPPR Vision #26: Overview of the NSA's TAWDRYYARD Radar Retro-Reflector  General overview of the NSA's TAWDRYYARD tracking beacon radar retro-reflector and the AM backscatter principle.  (YouTube)
  7. GBPPR Vision #27: Overview of the NSA's LOUDAUTO Radar Retro-Reflector  General overview of the NSA's LOUDAUTO audio-based RF retro-reflector.  (YouTube)
  8. GBPPR Vision #28: Overview of the NSA's RAGEMASTER Radar Retro-Reflector  General overview of the NSA's RAGEMASTER VGA video RF retro-reflector.  (YouTube)

Other Related GBPPR Projects

  1. GBPPR PHOTOANGLO Experiments
  2. Laser Bounce Listening Device
  3. Using Sunlight to Intercept Audio
  4. Doppler Stethoscope for E.O.D. Applications
  5. GBPPR Radar Experiments
  6. van Eck-style Radiation Interception Experiments
  7. Through-the-Wall Motion Detection Device
  8. Ultrasonic Surveillance Bug
  9. GBPPR Non-Linear Junction Detector  Try to recover audio via dissimilar metal junctions.
  10. Homebrew Lock-In Amplifier
  11. GBPPR Active Denial System  Experimenting with high RF power levels at 2.45 GHz.
  12. GBPPR Interferometric Surveillance Device Experiments - Part 1
  13. GBPPR Interferometric Surveillance Device Experiments - Part 2
  14. GBPPR Remote Respiration/Heart Beat Monitor Experiments
  15. GBPPR Remote Telephone Surveillance Experiments

Return to Homebrew Military & Espionage Electronics Page