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Leon Theremin and the 'thing'

Leon Theremin


Leon Theremin, (27 August 1896 – 3 November 1993) was a Russian and Soviet inventor, most famous for his invention of the ‘theremin’, one of the first electronic musical instruments and the first to be mass-produced. He also worked on early television research. His listening device, "The Thing", hung for seven years in plain view in the United States Ambassador's Moscow office and enabled Soviet agents to eavesdrop on secret conversations.



The ‘Thing’


The Thing, also known as “The Great Seal Bug”, was a passive covert listening device, developed in the Soviet Union and planted in the residence of the US Ambassador in Moscow, hidden inside a wooden carving of the Great Seal of the United States. It is called a passive device as it does not have its own power source. Instead it is activated by a strong electromagnetic signal from outside. The device was codenamed LOSS by the US and RAINDEER or DEER (ОЛЕНЬ) by the Soviets.


On 4 August 1945, the ”Vladimir Lenin All-Union Pioneer Organization”, presented a hand-carved replica of the Great Seal of the United States to US Ambassador Averell Harriman, as a gesture of friendship to the USSR's World War II ally. It hung in the library at the Residency Spaso House.



Unknown to the Americans however, the carving contained an RF radio bug of a novel design, in that it didn't have its own power source and was not connected via wires. Instead, the device was illuminated by a strong radio signal from the outside, which powered and activated it. It gave the bug a virtually unlimited life and provided the Soviets with the best possible intelligence.


The bug was finally discovered by the US State Department in 1952, three ambassadors later, during the tenure of Ambassador. George F. Kennan.


The device appeared to be hidden inside the wooden carving behind the ambassador's desk, and resembled a cylindrical microphone with an antenna rod connected to it. Tiny holes in the wood under the eagle's beak, guided the sound to the membrane of the bug that was mounted just behind it. When the Russians knew that an important meeting would take place, they parked an unmarked van in the vicinity of the residency 3 and illuminated the bug. A receiver, tuned to the bug's resonant frequency, was then used to pick up the conversation in the ambassador's study.


The discovery of the bug was kept secret for many years, until the 1960 U-2 incident [5]. On the 1st May 1960, the Soviets had shot down an American U-2 spy plane over Soviet airspace, as a result of which the Soviet Union convened a meeting of the United Nations Security Council, accusing the Americans of spying. On the 4th day of the meeting (26 May 1960), in an attempt to illustrate to the council that spying between the two nations was mutual, American Ambassador to the UN, Henry Cabot Lodge, revealed the Russian bugging device.



The Thing is a so-called resonant cavity microphone, consisting of a resonant cavity, combined with a condenser microphone. The diagram below shows the construction of The Thing, based on various publications and the original FBI report [46]. The device consists of a copper cylinder with a highly polished silver-plated interior, that acts as a high-Q resonant cavity of the reentrant type. At the center is an adjustable mushroom-shaped disc with a flat surface, which acts as a capacitor in combination with a thin 6.35µm membrane that closes the open end. An antenna enters the cavity through an insulated hole in the side of the cylinder and is capacitively coupled



The dimensions of the cavity are carefully chosen so that it is resonant at a very high frequency (e.g. 1700 MHz). It is then illuminated, or exited, by a strong signal from the outside, as shown in the illustration below. Any sound in the room (speech) causes the membrane to vibrate, which decreases and increases the space inside the cavity and also the capacity between the membrane and the mushroom. As a result, the bug produces a combination of Amplitude Modulation (AM) and Frequency Modulation (FM). In practice, only the AM component was used by the Russians.



About the author


Eur Ing Dr Robert Brown (Robert) is the Executive Director of Fraser George and Associates Limited and is a Consultant and Forensic Engineer in the fields Electrical Electronic and Control Engineering.


Robert is an accomplished professional Expert Witness having prepared and presented many court compliant reports and presented oral evidence within the High Court, Crown Courts and County Courts.


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