GABLE JOINTING

Hawke's Bay Herald-Tribune, Issue 150, 13 July 1937, Page 12

GABLE JOINTING

X-Ray 'Apparatus Used COOK STRAIT WORK A portable X-ray apparatus waB part of the engineers ' equipment in the laying of the new telephone cable across Oook Strait. It came into use for examination of the two joints, the cable being laid in three sections and the final splioe taking place in midstrait. Unlike the orainar y telegraph submarine cable with itB simple structure of a copper conductox the coaxial has a rnore intricate make-up. It contains a central eonductor surrounded by fine copper tapes, and then heavily insulated with paragutta upon which are wound six copper strips. Where the old type of cable worked on a direct current the most modern type utilises high frequency currents and thns, through the medium of delicately adjusted terminal equipment, the various frequencies can be separated to such an extent that the new Cook Strait cable will ultimately provide not only 25 channels for simultaneous telephone conversations but if necessary an equal number of duplex teleprintey circilits for telegraphy. When the cable joiuts were made at sea the greatest care had to be taken in centring the eonductor within its heavy insulation and also to properly wind the copper strips in relation to the coro. Air bubbles had to be avoided ip the splice and a peri'ect adhesion of the various layers of insulating material was essential. Oonsequently at intervals during the operation the Xray maehine came into use to give visual indication of the efficiency of this delicate splicing operation. Although this type of joint is quite new in the world and extreme aceuracy is required in its making, the cable jointers, despite the unusual eonditions, made a perfeet job, as the X-ray apparatus demonstrated. The cable is only one feature of this highly specialised communication system. It will have to be tested frequently every day, for a nionth or six weeks, by means of specially designed electrical measuring apparatus in order to determine its electrical eharacteristies under the temperatures at the bottom of Cook Strait. The observers thus obtain data necessary for the proper adjustment of the carricr terminal apparatus to be installed at Lyall Bay and Blind Eiver cable huts and at Seddon. The carrier equipment, which was made in London, has been shipped to New Zealand and will be installed soon after tlie oi ako raio electrical measurements of the cable havo been comploted.