How a Phone Cable was Laid Across the Ocean

On September 25, 1956, the first transatlantic telephone cable (TAT-1) began operating between North America and Europe.

The story of this achievement began almost 100 years earlier with the first transatlantic telegraph cable.  That cable, laid in 1858 after several aborted attempts, enabled England’s Queen Victoria to send a message to America’s President James Buchanan.  The message took more than 16 hours to transmit.  New York celebrated with fireworks that accidentally set City Hall on fire.  The cable itself completely failed after six weeks.

With 20th-century advances in telecommunications, attention turned to transmitting speech across the ocean, but there were numerous technological challenges.  A transatlantic cable would require vacuum tube repeaters at regular intervals.  Unfortunately, vacuum tubes had a normal lifespan of less than 20 years, even when they weren’t lying more than two miles underwater at the bottom of the ocean.  Moreover, if the cable-laying ship had to keep stopping to drop repeaters, the coaxial cable would develop kinks.

American and British engineers came up with a series of ingenious solutions.  Signal levels were carefully controlled to extend vacuum tube life.  Flexible repeaters were developed that could be wound over the cable drum.  Each repeater had a frequency-specific crystal to detect tube failure.  And gas tubes provided back up.

Following World War II, TAT-1 was laid between Scotland and Newfoundland over two years at a cost of $42 million ($367 million in 2014 dollars).  The cable was 1,950 nautical miles long, with 51 repeaters at intervals of 37.5 nautical miles.  TAT-1 operated for 22 years without a single tube failure.  Subsequent cables took advantage of semiconductor and transistor technologies.  The last coaxial transatlantic cable was laid in 1983; today’s cables use self-healing fiber optics.

“It is amazing to consider the risks that those pioneering engineers and entrepreneurs took,” says Agilent’s Jim Hollenhorst, who worked on TAT-8, TAT-9 and TAT-10.  “They had no fundamental understanding of what they were doing; it was largely ‘cut and try.’  Entire fields of mathematics and electronics were later developed to understand and fix what went wrong.”

Today, designers have tools such as Keysight’s (Agilent’s electronic measurement business) Advanced Design System to simulate everything in advance before anything is built.  Keysight measurement tools can test every component – whether electrical or optical – before it is assembled into the system.

Keysight recently demonstrated a series of test and measurement solutions for next-generation communications at ECOC 2014, the European Conference on Optical Communications.

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