The Thing, also known as The Great Seal bug, was one of the first covert listening devices (or "bugs") to use passive electromagnetic induction to transmit an audio signal.
Operating principles
The Thing was very simple by today's standards, but ingenious. It consisted of a tiny capacitive membrane (a condenser microphone) connected to a small quarter-wavelength antenna; it had no power supply or active electronic components. The device, a passive cavity resonator, became active only when 330 MHz microwaves were beamed to the device from an external transmitter. Sound waves caused the microphone to vibrate, which varied the capacitance "seen" by the antenna, which in turn modulated the microwaves that struck and were reflected by "The Thing". A receiver decoded the modulated microwave signal so the sound that the microphone picked up could be heard, in the same way that an ordinary radio decodes modulated radio waves into sound.
Theremin's design made the listening device very difficult to detect, because it was very small, had no power supply or active components, and did not radiate any signal unless it was actively being powered and listened to remotely. These same design features plus the overall simplicity of the device made it very reliable and gave a potentially unlimited operational life. Assuming that the device had never been discovered, it could easily have worked for 50 years or more.
Use in espionage
Theremin's device was embedded in a carved wooden plaque of the Great Seal of the United States. On August 4, 1945, Soviet school children presented the bugged carving to U.S. Ambassador Averell Harriman, as a "gesture of friendship" to the USSR's World War II ally. It hung in the ambassador’s Moscow residential office until it was exposed in 1952 during the tenure of Ambassador George F. Kennan[1]. It was then that the existence of the bug was accidentally discovered by a British radio operator who overheard American conversations on an open radio channel as the Russians were beaming microwaves at the ambassador's office. The CIA found the device in the Great Seal carving after an exhaustive search of the American Embassy, and Peter Wright, a British scientist and former MI5 counterintelligence officer, eventually discovered how it worked.[2][3]
United Nations
On the fourth day of meetings in the United Nations Security Council, convened by the Soviet Union over the 1960 U-2 incident where a US spy plane had entered their territory and been shot down, the US ambassador showed off the bugging device in the Great Seal to illustrate that spying incidents between the two nations were mutual and to allege that Nikita Khrushchev had magnified this particular incident under discussion out of all proportion as a pretext to abort the 1960 Paris Summit.[4]
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