IEEE - Aerospace and Electronic Systems - October 2022 - 40
History Column:
DOI. No. 10.1109/MAES.2022.3185022
The Great Seal
Hugh Griffiths , University College London, London WC1E 6BT, U.K.
The Great Seal (also known as " The Thing " ) was an ingenious
covert eavesdropping device deployed by the
Soviets against staff at the U.S. Embassy in Moscow. It
was devised by the Russian scientist Leon Theremin, who
also invented the electronic musical instrument which
bears his name (perhaps most familiar in the theme music
for the TV program " Star Trek " ).
It took the form of a carved wooden representation of
the Great Seal ofthe United States, approximately 0.6 m in
diameter. It was presented by the Young Pioneer Organization
of the Soviet Union to W. Averell Harriman, the
United States Ambassador to the Soviet Union, on August
4, 1945 (just months after the end ofWW2 in Europe), and
took pride ofplace on the wall ofthe study in his residence.
Hidden within the wooden carving was a passive radio
microphone, whose operation relied on the illumination of
the device by an external RF signal at a frequency around
of 330 MHz. As such, it was completely passive and
required no power supply. When the external RF signal
was present, the re-reradiated signal was modulated by the
audio picked up from the room, and could be received at a
significant distance. Some accounts argue that it was actually
a harmonic of the illuminating signal that was picked
up, which would have removed the need to suppress the
direct illuminating signal in the receiver.
The sketch in the following shows the internal
structure of the resonant cavity. It contained a diaphragm
that acted as a microphone, modulating the
scattering from a monopole antenna element by varying
the capacitance.
The device was eventually discovered in 1951 by accident,
when a British radio operator at the British Embassy
heard American conversations on a Soviet Air Force radio
channel. It was brought to the United States, and the principles
ofits operation investigated by the FBI and by theNaval
Research Laboratory.
Author's current address: Hugh Griffiths, University College
London, London WC1E 6BT, U.K. (e-mail: h.griffiths@ieee.org).
Manuscript
received 5 May 2022; accepted 13 May
2022, and ready for publication 21 June 2022.
Review handled by Daniel O'Hagan.
0885-8985/22/$26.00 ß 2022 IEEE
40
IEEE A&E SYSTEMS MAGAZINE
The Great Seal-about 0.6 m in diameter
(cryptomuseum.com).
Resonant cavity microphone principle.
OCTOBER 2022
https://orcid.org/0000-0002-9947-5553
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https://orcid.org/0000-0002-9947-5553
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http://www.cryptomuseum.com
IEEE - Aerospace and Electronic Systems - October 2022
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IEEE - Aerospace and Electronic Systems - October 2022 - Cover1
IEEE - Aerospace and Electronic Systems - October 2022 - Cover2
IEEE - Aerospace and Electronic Systems - October 2022 - Contents
IEEE - Aerospace and Electronic Systems - October 2022 - 2
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