Friday, June 19, 2009

Defeat and Revivial of Tubes

Vacuum tube, 1958In the 1950s new technology put cables ahead of radio. Small vacuum tubes that could operate under water for 20 years or more meant that amplifiers could be buried at sea with the cable. This boosted the cable's information capacity to the point that it could even carry telephone signals.

Small vacuum tubes like this could be buried at sea with the cable for years. They helped to increase a cable's information-carrying capacity by more than a thousandfold.
Vacuum tube, 1958
National Museum of American History, from TyCom



In 1956 AT&T teamed up with the British General Post Office to lay two cables across the Atlantic, each transmitting in a single direction. Together they could carry 36 telephone channels, and this soon expanded to 48. Other telephone cables soon followed, and the old telegraph cables became obsolete.

The new cables had a central copper conductor surrounded by a second coaxial conductor that provided a "return" path for the electricity. Instead of gutta percha, the insulator was polyethylene, a synthetic plastic that had been developed in the 1930s.
TAT-1, the first transatlantic telephone cable, 1956
TAT-1, the first transatlantic telephone cable, 1956
National Museum of American History, from Robert Lynch, Director, System Implementation, TyCom



Laying telephone cable by ship, 1960s
Laying telephone cable by ship, 1960s
Photograph by Ian Rowan



Transatlantic telephone cables
Courtesy of Corning, Inc.
TAT-11956 - 48 channels
Nefoundland - Scotland
TAT-21959 - 48 channels
Newfoundland - France
CANTAT1961 - 80 channels
Newfoundland - Scotland
SCOTICE-ICECAN1961-62 - 24 channels
Newfoundland - Scotland
TAT-31963 - 138 channels
New Jersey - England
TAT-41965 - 138 channels
New Jersey - France
TAT-51970 - 845 channels
Rhode Island - Spain
CANTAT-21974 - 1,840 channels
Nova Scotia - England
TAT-61976 - 4,000 channels
Rhode Island - France
TAT-71978 - 4,000 channels
New Jersey - England

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