New Cable Laid Under Atlantic

Sun (Auckland), Volume II, Issue 503, 5 November 1928, Page 14

New Cable Laid Under Atlantic

Latest Type Sends Ten Messages at Once LONGEST IN EXISTENCE The most strikingly significant answer that has been made to recent questions as to the effect radio communication is having on the transoceanic telegraph cables has just been provided by the laying of a new cable between Newfoundland and the Azores which will have the largest message capacity of any in existence, says the “Daily Mail.” For some time there has existed a surplus of cable capacity between the Azores and Germany, Spain, Italy and Northern Africa. Recent increases in the cable traffic of the Western Union Telegraph Company made necessary the laying of a new and faster cable between America and the Azores to utilise this surplus capacity. It is this cable, costing about £400,000, that has just been completed and will be in operation within the next few weeks. Special “Loading” It was obvious that higher speed could not be obtained by placing large induction coils at intervals along the ocean bed, as is done on underground thelephone lines to increase the volume of the transmitted voice whenever it begins to fade after travelling long distances. A special nickel and iron alloy was discovered, however, which would produce a similar result if wrapped round the entire length of the copper conductor of the cable. Messages could be sent over the cable at a much higher speed, because the iron alloy wrapping or “loading.” having high magnetic properties, kept the signals clearly separated when travelling at high speed, and prevented overlapping and jumbling of the characters.

Cables based on this design have been laid in both the Atlantic and Pacific Oceans since 1924, and the result has been a speedy capacity of five messages in one direction at a time over a single copper wire. The engineers wanted to send traffic in both directions simultaneously over the one small copper conductor, however. The very uniformity of the “loaded” cable proved a stumblingblock. Research quickly demonstrated that such high electrical efficiency throughout the entire length of the cable made “duplexing,” or two-way simultaneous sending, impossible. The answer to the problem was a cable combining the new "loading” principle with the old unloaded cable that has been familiar since the earliest days of ocean telegraphy. The high-speed portion of the cable was laid in the deepest part of the ocean. As the shore was reached at either end, however, a slower type of conductor was used, with the result that messages could move through each other when transmitted in opposite directions at the astonishing rate of 1,500 letters a minute in each direction, or five messages eastbound and westbound—ten simultaneous messages in all!

This revolutionary type of design required that the cable be of an exact length pf 1,341.17 miles. Never before in the history of cables had such a restriction as to exact length been imposed. The Western Union Telegraph Company put the problem of laying to the Telegraph Construction and Maintenance Company, of London, the organisation that manufactured the first Atlantic cable. The Telegraph Construction and Maintenance Company immediately assumed the task of manufacturing and laying the cable, despite the fact that the exact amount of cable to be laid between Bay Roberts, Newfoundland, and Horta, Fayal—the telegraph relay point of the Azores—l,34l.l7 miles, was definitely specified. This meant that the cable ship must maintain an exact course, regardless of wind or weather, and that the cable engineers should lay the exact linear footage required to conform to every mountain peak and valley along the ocean bed over the route selected. Thirty Anxious Hour Any additional mileage beyond that specified would seriously have unset the electrical properties of the cable necessary to the required message speeed. The cable steamer Dominia, the largest vessel of her type, left Newfoundland late in August, trailing the cable behind her. For four days everything moved like clockwork. Mile after mile of cable went over the stern and settled on the bottom of the ocean. Communication was being maintained between the shore and ship through the cable throughout the progress of the work. But on the fourth day the ship entered the outer edge of a cyclone Clouds prevented / the taking of observations. The pitch and roll of the ship placed the cable, less than an inch in diameter at the deep-sea portion, in constant jeopardy. Cable engineers stood by the paying-out brakes with eyes glued on the instruments registering the strain on the cable. Navigating officers estimated the drift due to wind and currents. And so perfectly had the cable engineers calculated the distance along the bed of the ocean and the amount of slack required to cover it that a break in the clouds, after 30 hours, made possible the taking of solar observations that told of a course adhered to and a correct mileage of cable paid out.

After three days in the cyclonic storm the Dominia dropped anchor in the harbour of Horta, seven days on* of Newfoundland, with the required mileage laid along the predetermined route.

When certain engineering tests have been completed, the new cable will be placed in operation. Engineers are of the opinion that its revolutionary character will have an important bearing not only on future cable design but also on the continued increase in ocean cable traffic.