a website collaboration between Science Service and the Smithsonian Institution

1964 - network of 24 channels with a total of more than 450 sound powered telephones


CD 2055076 E&MP7.016



A network of 24 channels with a total of more than 450 sound powered telephones, which derive their power solely from the human voice, provide the communications between the East Area central blockhouse (left) and the various test stands at NASA’s George C. Marshall Space Flight Center here.

All external electrical power connections and batteries are eliminated in the sound-powered telephone set up which furnishes reliable voice contact between technicians at test stands over an area of approximately one square mile and personnel in the central blockhouse where test data are recorded. The unique, shock-proof telephones are made by United States Instrument Corporation of Charlottesville, Va.

Elimination of an outside source of power means that the equipment will continue to carry voice conversations even in times of power failure. Also, since the sound-powered telephone apparatus operates on low level audio voltage, the system cannot influence sensitive electrical or electronic devices used in test areas.

Basically the system works like this: when the voice strikes the transmitter diaphragm, vibrations occur in the magnetic circuit behind the diaphragm, creating an alternating current. This low level current travels by wire to the receiver on the other end of the line, where it creates sound waves that reproduce the speaker’s voice. Sound can be transmitted by wire as far as 30 miles.

The Space Center’s sound powered telephone system, made up mainly of U.S.I. head and chest sets which leave the hands free to operate machinery or for other tasks, connects the blockhouse to static, dynamic and component test stands in the Center’s East Test Area. Included in the communications network are the Saturn I test stand and a single-engine stand. Several new positions will be added in 1964.

The photo on the right shows an 80 foot tall Saturn I booster being captive-fired before it is shipped to Cape Kennedy for launching.  

Original Caption by Science Service
United States Instrument Corporation

National Museum of American History


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