John Leavitt, age 12, of Garden Grove, California, for his question:
How many phone calls can an underwater cable carry?
Undersea telegraph cables came first, long before the first telephone cable was laid on the floor of the ocean. For years, all overseas calls traveled by radio. Now some of these calls are carried by cable and better cables of the future will carry many more of them.
Overseas telephoning grows more popular every year. In 1964, Americans had almost 6 1/2 million conversations with their friends across the oceans. It is estimated that in 1970 the number of these calls will reach about 15 million. Extra circuits to carry them by radiotelegraph are being installed all the time. And in the past ten years, more than 600 snore telephone cables have been laid across the floors of the oceans. Naturally, these systems are improved constantly with new inventions. An underwater cable of the future promises to carry over five times as many calls as the best ones of today.
The first transatlantic telephone cable was ready for conversations in 1956. It was able to carry 36 conversations at the same time. In a few years, underwater phone cables linked California with Hawaii, Florida with Puerto Rico, Jamaica and the Virgin Islands, Alaska with Seattle. More cables were added across the floor of the Atlantic and others were laid to link Canada and Australia, Hong Kong and Malaysia.
A cable is a tight rope of many wire cords. The early cables were twin systems that needed separate lines to carry the two sides of a conversation to and fro in opposite directions. Until 1960, the best of them could carry only 36 calls at a time. Then an idea called Time Assignment Speech Interpolation led to a new invention. TASI gadgets were added to boost some of the old cables. Instead of 36 conversations, these improved cables were able to carry 84. One improvement leads to another. A single cable was designed to carry more calls than the old twin system, even with its TASI boosters. This was an American idea from the Bell Telephone people and since 1963, all our new undersea lines have been laid with these single cables. They can carry 138 two way conversations at a time. The type of cable laid by the British carries only 80 calls at a time.
Our inventive telephone experts, however, are never satisfied. They now have plans for a super capacity cable that will out do all the others. The super line is expected to be ready for calls next year between Florida and the Virgin Islands. It promises to carry 720 two way conversations at one time. If we keep our conversations short, hundreds of us can chat over this super line every day.
The rope of wires in an undersea cable must be inside a hard shield to protect it from bashes. It must have a chemical proof outer sheath to save it from the salty water. Tremendous supplies of electric power are needed to transmit sounds over their long journeys. But even so, the sounds fade as they travel. Amplifiers are built into the cable to strengthen them and boost then on their way. As a rule, an amplifier is an electronic.tube. In the super cable of the future, this fob will be done much better by more durable transistors.