The total weight of the unit, including the antenna, was 1.1 ounces (31 grams). The antenna was capacitively coupled to the post via its disc-shaped end. The post had machined grooves and radial lines into its face, probably to provide channels for air flow to reduce pneumatic damping of the membrane. In the middle of the cavity was a mushroom-shaped flat-faced tuning post, with its top adjustable to make it possible to set the membrane-post distance the membrane and the post formed a variable capacitor acting as a condenser microphone and providing amplitude modulation (AM), with parasitic frequency modulation (FM) for the re-radiated signal. Its front side was closed with a very thin (3 thou, or 75 micrometers) and fragile conductive membrane. The cavity was a high-Q round silver-plated copper 'can', with the internal diameter of 31⁄ 40 in (19.7 mm) and about 11⁄ 16 in (17.5 mm) long, with inductance of about 10 nanohenries. It used a straight rod, led through an insulating bushing into a cavity, where it was terminated with a round disc that formed one plate of a capacitor. Given the radio technology of the time, the frequency of 330 MHz is most likely, equivalent to a wavelength of 91 cm). The device consisted of a 9-inch-long (23 cm) monopole antenna (quarter-wave for 330 megahertz frequencies, but it was also able to act as half-wave or full-wave the accounts differ. These same design features, along with the overall simplicity of the device, made it very reliable and gave it a potentially unlimited operational life.ĭesign The seal opened exposing the Soviet bugging device, on display at the NSA's National Cryptologic Museum. Its design made the listening device very difficult to detect, because it was very small, had no power supply or active electronic components, and did not radiate any signal unless it was actively being irradiated remotely. A receiver demodulated the signal so that sound picked up by the microphone could be heard, just as an ordinary radio receiver demodulates radio signals and outputs sound. The movement of the membrane varied the capacitance 'seen' by the antenna, which in turn modulated the radio waves that struck and were re-transmitted by the Thing. Sound waves (from voices inside the ambassador's office) passed through the thin wood case, striking the membrane and causing it to vibrate.

This is referred to in NSA parlance as 'illuminating' a passive device. The device, a passive cavity resonator, became active only when a radio signal of the correct frequency was sent to the device from an external transmitter. The Thing consisted of a tiny capacitive membrane connected to a small quarter-wavelength antenna it had no power supply or active electronic components. Because it was passive, needing electromagnetic energy from an outside source to become energized and active, it is considered a predecessor of radio-frequency identification ( RFID) technology.

Averell Harriman, the United States Ambassador to the Soviet Union, on August 4, 1945. It was concealed inside a gift given by the Soviet Union to W. The Thing, also known as the Great Seal bug, was one of the first covert listening devices (or 'bugs') to use passive techniques to transmit an audio signal. Covert listening device Replica of The Thing which contained a Soviet bugging device, on display at the NSA's National Cryptologic Museum

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