In 1946, Soviet school children presented a two foot wooden replica of the Great Seal of the United States to Ambassador Averell Harriman.
The Ambassador hung the seal in his office in Spaso House (Ambassador's residence). During George F. Kennan's ambassadorship in 1952, a secret technical surveillance countermeasures (TSCM) inspection discovered that the seal contained a microphone and a resonant cavity which could be stimulated from an outside radio signal.
May 26, 1960 Ambassador Henry Cabot Lodge, Jr. displays the Great Seal bug at the United Nations.
On May 26, 1960, U.S. Ambassador to the United Nations Henry Cabot Lodge, Jr. unveiled the Great Seal Bug before the UN Security Council to counter Soviet denunciations of American U-2 espionage. The Soviets had presented a replica of the Great Seal of the United States as a gift to Ambassador Averell Harriman in 1946. The gift hung in the U.S. Embassy for many years, until in 1952, during George F. Kennan's ambassadorship, U.S. security personnel discovered the listening device embedded inside the Great Seal. Lodge's unveiling of this Great Seal before the Security Council in 1960 provided proof that the Soviets also spied on the Americans, and undercut a Soviet resolution before the Security Council denouncing the United States for its U-2 espionage missions. U.S. Department of State
A Brief History of Russian Spying Henry J. Hyde, Republican of Illinois Russia's notoriety for eavesdropping and espionage stretches back even to the czars. James Buchanan, U.S. minister in St. Petersburg during 1832-33 and later U.S. President, recounted that 'we are continually surrounded by spies both of high and low degree. You can scarcely hire a servant who is not a secret agent of the police.'
An 1850-53 successor, Neil S. Brown, reconfirmed that 'the opinion prevails that ministers are constantly subjected to a system of espionage, and that even their servants are made to disclose what passed in their households, their conversations, associations, etc.' Otto von Bismarck, who represented Prussia from 1859 to 1862, stated 'it was especially difficult to keep a cypher secure at St. Petersburg, because all the embassies were of necessity obliged to employ Russian servants and subordinates in their households, and it was easy for Russian police to procure agents among these.' The tradition intensified and became more sophisticated under the Bolsheviks and their successors. The wife of the Italian ambassador in Moscow during 1927-30 said: 'Spying on the part of the authorities was so common as not even to be thought of as spying.'
Nonetheless, Western laxity in the face of these dangers also has deep roots. A confidential 1940 memo to the White House from FBI Director J. Edgar Hoover related the results of an investigation triggered by British complaints that shared intelligence was being leaked to the Soviets through the Moscow embassy. The memo revealed that single U.S. employees in Moscow frequented a prostitution ring linked to Soviet intelligence and that classified documents were handled improperly and may have been obtained by Soviet workers. The code room was found open at night, with safes unlocked and code books lying on the table.
By the 1930's, technical eavesdropping supplemented human espionage. Guests at Spaso House, the U.S. ambassador's residence, at one point were given cards welcoming and warning them: 'Every room is monitored by the KGB and all of the staff are employees of the KGB. We believe the garden also may be monitored. Your luggage may be searched two or three times a day. Nothing is ever stolen and they hardly disturb things.'
In 1952, the Soviet gave U.S. representatives a carved wooden replica of the Great Seal of the United States. It hung prominently for years, at least part of the time in the ambassador's study, before a tiny microphone was found in the eagle. George Kennan's memoirs describe the event. In a theme now familiar, Kennan relates that Spaso House had been redecorated under Soviet supervision, without the presence of any American supervisors, giving them opportunity 'to perfect their wiring of the house.' 'The ordinary, standard devices for the prevention of electronic eavesdropping revealed nothing at all,' but technicians decided to check again, in case our prevention methods were out of date.
'Quivering with excitement, the technician extracted from the shattered depths of the seal a small device, not much larger than a pencil . . . capable of being activated by some sort of electronic ray from outside the building. When not activated, it was almost impossible to prevent. . . . It represented, for that day, a fantastically advanced bit of applied electronics.'
In displaying this equipment to the United Nations, Henry Cabot Lodge, Jr. charged that more than 100 similar devices had been recovered in U.S. missions and residences in the U.S.S.R. and Eastern Europe. Jacob Beam, U.S. ambassador from 1969 to 1973, wrote that the 'ever-present pressures' or residing in the U.S.S.R. included 'physical surveillance, and constant bugging of conversations by various types of concealed devices.'
Such Soviet monitoring techniques have been regularly discovered and occasionally publicized during the postwar period. Incidents revealed during the 1980's alone are alarming in their scope and seriousness. In 1982, we verified indications that the new embassy building had been penetrated. In 1984, we found that an unsecured shipment of typewriters for the Moscow Embassy had been bugged and had been transmitting intelligence data for years. In 1985, newspapers revealed that the Soviets were using invisible 'spydust' to facilitate tracking and monitoring of US diplomats. In December 1986, Clayton Lonetree's confession revealed that the Soviets had recruited espionage agents among Marine Guards at the embassy. Recently, we found microphones that had been operating in the Leningrad consulate for many years.
Although Moscow had developed over centuries a reputation for severe counterintelligence risks, and although the postwar period was replete with examples of this, U.S. State Department and embassy personnel continued to act like babes in the KBG woods. The Congressional Record Henry J. Hyde, Republican of Illinois.
Note: Do not rely on the frequency or wavelength figures. See *** below.
"Electronic eavesdropping is not new. But until the Watergate incident, the general public knew little about it. This innocence was first challenged in 1960, when Henry Cabot Lodge, Jr. displayed the now infamous Seal bug to the United Nations as an example of Soviet spying on this country (USA). With this dramatic revelation, bugging first became almost a household word, and widespread public interest has persisted ever since.
The triumph of the Great Seal bug, which was hung over the desk of our Ambassador to Moscow, was its simplicity. It was simply a resonate chamber, with a flexible front wall that acted as a diaphragm, changing the dimensions of the chamber when sound waves struck it. It had no power pack of its own, no wires that could be discovered, no batteries to wear out. An ultra-high frequency signal beamed to it from a van parked near the building was reflected from the bug, after being modulated by sound waves from conversations striking the bug's diaphragm.
The Great Seal launched electronic snooping as no other incident could. The feeling in many circles seems to be that if such appalling tactics are employed by major world powers, lesser applications would hardly be as startling, if indeed not justifiable."
Q. What does "Good Vibrations" by The Beach Boys have in common with the Great Seal's bad vibrations?
A. They both contain a Lev Termen (aka Leon Theremin) invention.
If Thomas Edison had come of age in Lenin's Soviet Union, he might have led the double life of Lev Termen. Among Termen's myriad prescient brainstorms were the first electronic surveillance system, a gadget that opened doors at a hand signal and a 1920's version of television that broadcast 100 lines of resolution onto a five-foot-square screen - far superior to any competitor. For decades he worked in "mailboxes," top-secret Soviet research centers, on countless, still-undisclosed projects for the vast Soviet security apparatus. Those we know of include the listening device hidden in the Great Seal of the U.S. Embassy in Moscow and exposed in 1960 at the United Nations by Henry Cabot Lodge, Jr.
But in the West Termen became famous as Leon Theremin, who in 1919 created an instrument named after him, a radio-sized box that, with a carefully precise wave of the hands over its antennas, produced sounds that Depression-era listeners found uncanny, heavenly, astounding, unsettling or puerile. As composer Albert Glinsky rightly insists in his exhaustively researched and revealing biography, this frequently clumsy instrument was the first foray into the brave new world of electronic music. Essentially a radio-feedback device, it was impossibly sensitive, often screeched out of tune, required ridiculously deft technique while being advertised as the perfect instrument for the musically illiterate, and was plagued with problems from irreducible portamento (gliding) to unvarying tone and timbre. Still, its magic captured the imagination of millions and has since invaded pop culture, from the eerie theme for the 1930's radio show "The Green Hornet" to movies like "Spellbound."
In the early 1950's, 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 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 Britian's MI5 discovered the principle by which it operated. MI5 later produced a copy of the device (codename SATYR) for use by both British and American intelligence.
How the Thing worked. 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 plate. These variations altered the charge on the antenna, creating modulations in the reflected radio beam. These were picked up and interpreted by the receiver.
The Great Seal bug was discovered in 1952, but its existence was not made public until 1960.
However... here is one interesting leak.
In 1958-9, Richard F. Schwartz (Moore School of Electrical Engineering of the University of Pennsylvania) wrote the following in a book called The Eavesdroppers...
"... a microphone vibration measuring device has recently been proposed, in detail, by Stewart (Chandler Stewart, "Proposed Massless Remote Vibration Pickup," Journal of the Acoustical Society of America, July 30, 1958, pp. 644-645)..."
"... Another report, allegedly published in a Washington paper although search failed to verify it, mentioned a device beamed into the Russian embassy to pick up conversation there. Supposedly, the beam was aimed at the centerpiece of the Russian emblem, but whether there was a transponder there, or whether this piece was just a convenient metallic surface, is not certain. At any rate, such reports lend credibility to the explanation given here."
Readers were cautioned in the book's Introduction that ...
"Because of our promise to conceal the source of information where concealment was requested, the factual report necessarily omits naming many names and places, and often disguises a factual situation so as to prevent an identification with the original occurrence, but preserves all the while the basic truth of the occurrence and its relevance to the sturdy."
In short: the 'Washington paper' report was probably fictitious; it was not the Russian embassy; not the Russian seal; and it definitely was a transponder (Why else mention it?). Word about The Thing was now out.
Information from confidential sources... "Initially, I can only add that Peter Wright, formerly of MI5 said in his book "Spycatcher" (pp. 20, 62, 116, 292) that he had interviewed German scientists who had been repatriated from Russia (where they had been taken at the end of WWII). He claimed that they said that they had developed the system for the Soviets. The basic problem back in those days was to develop a decent amount of clean RF energy up at UHF. In that development process the scientists produced small "target" devices to use as markers in testing their radar systems. It is my suspicion that someone who had used such devices decided to put a flexible wall in that device to make it into a microphone. That's just a guess however.
Also, I interviewed a little old man 10 or more years ago who I happened to meet at a trade show. The things he said convinced me that he had indeed had access to information on the discovery of that device and another device in Warsaw. Only someone with access to classified information would have known the details that he related. Unfortunately, I misplaced his card and have no recollection of his identity now (I'm afraid that that anecdote sounds like something that would appear in the National Enquirer).
Rumor was that the Brits had prevented the signal from the passive cavity resonator and alerted us to its presence. The little old man said that he had been carrying a audio amplifier from a thing called a Schmidt Kit*, around in the attic of Spaso House. The amplifier he used had a crystal diode in series with a short wire rod that acted as an antenna at the audio input connector. He couldn't say how he happened to be using that sort of rig at the time. (Possibly someone had told him to do so because that's what the Brits had done. That part of the story is still vague).
He said that when he got over the vicinity of the ambassador's office, he could hear the ambassador talking in the office below (through the amplifier). He then went below, knocked on the door of the ambassador's office and called the ambassador out into the hallway to tell him what he had observed. The ambassador understood and asked him to come in to carry on his inspection. The ambassador kept up a conversation on other matters during the process. The tech soon discovered that the signal was emanating from the great seal. He first suspected that there was a transmitter in the wall behind the seal so he lifted the seal from the nail from which it was suspended and put it down on the floor. The signal disappeared. He could see no evidence of an installation in the wall behind the place where the great seal had been.
He put the seal back up on the wall with no reappearance of the signal. Then, suddenly the signal came back on. He surmised that the device in the great seal might have been getting its operating power from the nail in the wall but knew that it was not possible because there was only one conducting path for electric current and that was the nail.
Ultimately, they discovered the device inside the seal itself and the little old man did not seem to know the details of that part of the work.
We got what was probably a copy that was fabricated by the Brits. I'm not sure about that, but it makes sense. It came to me through our R&D people who did interface with the Brits. Us ops-types weren't usually introduced to the Brits for operational reasons. We were friends but we didn't want to run across them in the field and raise the spectre of operational activity when we didn't want to.
I took the unit to a training facility where there was plenty of space and tested it with very good results.
Later, we built our own, more elaborate device and I installed two of them operationally. They sounded like plain old FM bugs when operating. Our problem was to keep from sterilizing people with the signal at the LP end. I suspect they are still in place in those targets."
(We sincerely appreciate this contribution from a first-hand source. Thank you for adding to the history of The Thing. ~Kevin)
P.S. * "So, uh... what's a Schmidt Kit?" The Schmidt Kit consisted of a radio receiver that would tune over a limited frequency range (centered on 70 MHz I think) and that had headphone output only (no speaker). There was also the audio amplifier with a phono jack for the input and headphone output. An induction coil for use against telephone lines (I think) and possibly a metal preventor were also included. There was an eavesdropping transmitter for VHF that was battery operated and I think one for operation from the a.c. mains. The one operating from mains power used a number of resistors to drop the mains voltage down to that needed for the filaments for the tubes. The resistors got warm enough to cook food on and the entire thing would burn up when put into a masonry wall, etc., which acted like an oven. (The mains power transmitter might have been sold separately.)
It all fit into a normal-sized briefcase (tan colored) and there was a simple combination lock on the latch.
It was manufactured up in the NY City area and marketed to law enforcement, etc.
All of the electronics used vacuum tubes as there were no transistors in those days.
Dear Mister Murray:
Your article on The Great Bug Story is very interesting. I may be able to add to your knowledge of the device which in the post Soviet press received a big mention after Doctor Theremin’s death. It is called Buran, translated “storm”.
I am a retired former US Army Sergeant who in my military profession was a radar repairman. In early 1955 I was assigned to a Signal Corps technical intelligence unit in Japan. It had 5-6 enlisted men and one junior officer. Its mission was to perform preliminary field analysis of captured enemy material (CEM) on largely communications related equipment and other activities tasked to us. We had a shop with test equipment and a photography facility. I was sent here because of a previous assignment in this kind of activity.
Later that year our primary mission was expanded to include technical support to various intelligence activities in the Far East Area. Three field engineers (Tech Reps) arrived and were given assignments which will not be discussed. In 1956 came a young solider, a PFC with a Ph.D. in Electrical Engineering. In those years, there was no Military Occupational Specialty (MOS) for Ph.D. as they and EEs got the same MOS 333 for electrical research assistant.
Meanwhile, a special requirement came from a customer for a certain kind of bug. I was assigned to Ph.D. as his assistant because of experience in radar and microwaves. He was tasked to design a bug based on Theremin’s device. In a security secure location we were given a demonstration of how a room is swept for such bugs. We were given the opportunity to physically examine the test bug but were not permitted to disassemble it. It operated somewhere between 1.1 GHz and 1.5 GHz.
Back in the shop, Ph.D. started to calculate the design for his device. We obtained a 3 GHz Radar Echo box and an RF Signal Generator used in radar testing to see how the echo box would react when energized. One end was removed and covered with a metallic foil. Its reaction to sound showed as deflections on the meter, the activity we were looking for.
The design was completed and the component parts were fabricated in 2 or 3 secure machine shops, none of which would have had parts for a complete assembly. We did all the silver plating in our shop. The parts were assembled but we needed a receiver to test it. A chassis was purchased on the Japanese market on which one of the engineers designed a four miniature vacuum tube high gain audio amplifier. We found a crystal diode adapter used for radar testing which we modified to hold the rod antenna on one end. Inside the adapter was a 1N21B cartridge crystal normally used in crystal mixers (converters) at the front end of some radar receivers. The prevented output which was audio was coupled into the amplifier which was microphonic and had a high noise level. Our device was energized by the RF signal generator which gave a low power output even when turned to maximum output. Anyhow, the bug worked and the design considered successful. We found them to have a dominant mode and also to resonate at other frequencies which may have been useful. Also discussed was how much of the bug's emission was either AM or FM or did it do both. We were handicapped by time and the non availability of proper test equipment to carry the experiments further. All of it was very interesting.
The nickname Error Indicator was attached to the device. At some time in the 1970's or 80's I saw the nickname mentioned in a New York Times article on eavesdropping. I think it was described well in Spycatcher or another book where the diaphragm in the Soviet bug was damaged during disassembly as it was very thin and fragile. Our diaphragm was made from the thinnest copper sheet available and silver-plated. It is probable that the performance of our bug would have been improved with a very thin foil.
I think the exterior appearance of our bug was based on the one we examined at the sweeping demonstration which we thought was a copy of the Soviet piece. Ph.D. took note of a visible bit of the innards through the small vent holes and took it from there, although, we had no knowledge of what really was inside. Both bugs had small vent holes, about 1/8 inch, spaced equidistantly on radii on both ends. The Soviet bug shown on page 5 has very large vents.
The story says that more than a 100 similar bugs were found. Were they all alike? Were there improvements made to them? The bombardment of the Moscow embassy with microwaves leads me to believe that there were other bugs, or none, to cause harassment and fear in employees and to keep us guessing.
Our unit was disestablished in December 1957 and I went back into radar. There was much interesting and productive work done in our little shop. I think those in the community who were our customers didn't want to see us shut down. In 1963 I was returned to the intelligence community in Europe where I was a Radar and Electronic Warfare Systems Analyst, an impressive title. In retired in 1967 after twenty years of service. I hope you found my story interesting.
(I did... extremely interesting. Thank you. ~Kevin)
From a trusted source who has requested anonymity - added 2/15/10
"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 it's 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."
*** Our source brings up several interesting points: • the antenna's wavelength, • the size of the cavity, • and the reason this type of bug is not found in common use.
It appears the exploded view of The Thing (above) is mistaken. The antenna length was probably a rough guess, based on the original photo. The frequency of operation was likely calculated based on this guess, using a 1/4 wavelength formula.
As our source perceptively pointed out, the figures do not make sense.
Using the original photo, the antenna length appears to be closer to 8.5 inches. That coupled with a frequency of operation (1.1-1.5 GHz) provided (above) by our retired U.S. Army Sergeant technician who actually examined The Thing, calculates the antenna as being... one full wavelength!
This makes better sense, as so does the physical size of the resonate cavity, now.
In addition to the reasons our source lists for this type of bug falling out of favor, there is one more... A very powerful microwave radio signal is required to make this bug work. (You may remember hearing about the embassies in Moscow being bombarded by microwave signals.) One can get away with this unchallenged, in a closed society, if you are the government, and no one knows the reason for the signals. Today, in most of the world, a powerful microwave signal like this would be instantly discovered, tracked to the source and challenged.
The Thing was a good thing while it lasted, however, we can not become complacent. This technique still has value when used in a lower power and highly focused manner. The technique also works at other frequencies, like light (laser beam eavesdropping). ~Kevin
From a source who has requested anonymity - added 4/29/12
I am a former Foreign Service Officer.
I have a certain amount of first hand, and a larger amount of 2nd hand knowledge about the thing, having worked for a couple of years in the early 1960s in the organization that was responsible for dealing with it and all similar problems - the division of technical services of the office of security of the department of state: abbreviated as O:SY/T.
I knew the tech who actually discovered the thing (slightly), and heard from him in detail exactly how he found it. Some of your published accounts are a little inaccurate, but not essentially so.
It was found using a basically untuned crystal video receiver, so we did not know what the activating frequency was. Much more sophisticated tech surveillance countermeasures receivers came into use later.
In the early 1960s the device and the great seal were both on display in SY's little conference room - the room used for briefing people on technical surveillance countermeasures problems, and I got to handle and inspect them both many times. I also studied the various reports on how it functioned, prepared by several US Government labs and contractors. I also got to see and study various US government versions and developments from the thing.
The State Departments overseas facilities were very high priority and highly vulnerable targets for Soviet-bloc intelligence, so we got to experience, so to speak, many more and much more interesting tech surveillance attacks than other parts of the US government. The recognition of this fact led to the launching of a very serious science-based tech surveillance countermeasures effort.
We did get launched, to a significant extent, by the Brits, but that is more a 1950s than a 1960s story.
The bald gent shown in your photo with Mr. Reilly is Bud Hill, the then director of SY/T, my boss in the early 1960s. A first-rate scientist, although he tended to depreciate that and describe himself as being 'only an electrical engineer'. His hiring by the Department of State marked the beginning of a serious American scientific response to tech surveillance countermeasures.
The great seal device was inherently resonate at multiples of a particular frequency, and this gave rise to a certain amount of confusion (in some places) about the frequency of the signal that activated it. As a consequence of its extreme simplicity it also inherently created both AM and FM modulation, so there was again some confusion about the character of the surveillance receiver. It was probably a straightforward zero-IF receiver that delivered the amplitude modulation of the re-emitted signal as audio output.
A drawing and description of the device was published in Scientific American sometime in the 1960s or early 1970s - in connection, if I recall correctly, with the amateur scientist column. I was, to say the least, surprised to see it. It was very accurate. (left)
The carved space within the seal indicated that the device found was a later generation device - the earlier one(s) had been bigger. And the Soviets much have changed them out from time to time, as improvements were made.
Our inspect-able transparent room-within-a-room acoustically secure conference rooms were one response to tech surveillance problems. I was in charge of that program for a while. They have been widely discussed elsewhere - and were shown off by the Iranians, so they are not so secret, and I have nothing to add about them.
O:SY/T had several early significant successes, due to a combination of new science, more scientifically trained people, greater cooperation from other agencies, etc..
During my service in O:SY/T we pulled a huge wired microphone array out of the embassy in Moscow. 57 of them, if I recall. The event was described in the NY Times at some length.
Someone should do a complete and science-based account of "The Moscow Signal"; a technical surveillance story that continued through the 1960s and after. It is, I think, a much more interesting story than that of the Great Seal device, and it very likely had its origins in the same organization. They are both 'spy beam' stories.
You have not mentioned many of the individuals who were important to the US scientific response to soviet tech surveillance, but I do not feel able to or entitled to present the fuller story. Other than to note that I feel that the driving intellectual force behind this was the Department of State, and not the CIA or some part of the Department of Defense. I have noted a tendency by some to rewrite history about this.
You might want to follow up on the events connected to the departure of Otto Otepka. His presence in the Department of State as a spy for the McCarthy people in congress - after McCarthy's departure - did the Department of State and especially its Office of Security great harm. The 'events' (see the NY Times) resulted in both Reiley's and Hill's forced departures.
My last acts in that unfortunate drama were to urge, in a meeting with associates from CIA, NSA and other agencies, that some attempt be made to shift some of SY/T's TEMPEST-related activities out of State and more into the direct management of my organization's natural organizational competitors - the CIA...
I have just stumbled over the Scientific American article that I mentioned.
The description and drawing in Scientific American appeared in March 1968 at pages 132-133. The drawing is very accurate, but is not accompanied by much description. For example, it shows, but not mention, that the pedestal face adjacent to the diaphragm is not smooth. It had, if I recall, machined groves and machined radial lines, presumably to reduce any air cushion effect as the diaphragm vibrated.
The pedestal and diaphragm together made up a sort of air-variable capacitor, which altered the resonant behavior of the cavity.
I do not recall there being any vent holes designed to avoid an air-cushion effect; I question any description that says that their were some.
The story of how we couldn't figure it out, and that we relied on the Brits to tell us how it worked is, to say the least, an exaggeration.
It was studied by some of our premier scientific establishments, and well understood by them. If I recall correctly, The Navel Research Lab (a not sufficiently known body), Bell Labs, and a special commission put together by the National Academy of Science all looked at it - I remember being quite impressed by some of the studies. They addressed both the device itself and some very significant improvements that could be made to it.
Some research turned up quite old French and German patents and other publications that could have inspired the device, The French had a communication system for taxicabs that operated on a somewhat similar principle - a super-regenerative transponder that only 'came on' (emitted a modulated signal) when the central station sent out a query signal that pushed the local oscillator into action.
Our aim was to greatly increase the Q, so that it would not respond to any old source, but only to one of a specific frequency. Increasing the Q also increased the modulation, effectively increasing the maximum distance between the power source and the device.
The diaphragm excursion was, if I recall correctly, very small. The diaphragm was quite delicate. I think that a military lab that played around with it found that out to their sorrow.
Later models had a much more complex interior structure - one had a helical member, instead of a post - supporting the non-moving plate of the 'variable capacitor'. Probably part of the effort to increase the Q. I recall seeing US versions with dipole rather than monopole antennas. And I know that the Germans also worked up advanced versions of their own.
Battery operated bugs that could be switched on and off remotely were and are pretty common.
Great Seal-like devices were eventually entirely superseded (at least in high-threat environments) by devices that were powered by radiate energy that stored that energy and that could be switched on and off without regard to whether the power source was active or not.
But more primitive Great-Seal like devices devices that did not store energy continued to be used by major powers in third world countries for years.
The development of systems that stored radiated power and that could be switched on and off remotely, and other information, tended to make some of us believe that the Moscow Signal was not a radio-biological weapon at all, but rather part of an evolved bugging system.
All this soon led to devices that drew their power from strong rf fields that were 'naturally present', like those arising from local TV transmitting stations, and that could also be switched on and off remotely - by very subtle and hard to detect signals.
As detection systems improved, the bugs also evolved, returning signals with modulation schemes (eg spread spectrum) designed to avoid quick and easy discovery - at least by the counter-surveillance receivers of the day.
The evolution was intended, of course, to eliminate the ability to detect Great-seal type devices by simply illuminating the bugged area with a swept frequency transmitter and looking for an AM or FM modulated return of the frequency being used. I notice that even today some venders of bug-detection systems have never progressed past this point.
Later on, devices that stored collected data and delivered it in well-hidden bursts, on command, came into use.
I know of nothing that indicates that the Soviets were using that technology for these purposes in the early 1960s. The recording devices in use back then were simply too bulky, power-consuming and unreliable. Consider the failures of such devices in the early era of space satellites and undersea and underground cable tapping ventures.
I believe that everything that I have mentioned here is both long-since public knowledge, if not actually declassified, as well as being very old technology - as I have not been in the business in any way for almost fifty (!) years.
Thank you for sharing your most interesting and illuminating contribution to the history of The Great Seal Bug. ~Kevin