CABLE JOINTING.

Manawatu Standard, Volume LVII, Issue 195, 19 July 1937, Page 5

CABLE JOINTING.

X-RAY APPARATUS USED. HOW THE COAXIAL CABLE WORKS. A portable X-ray apparatus was part of the engineers’ equipment in the layiiig of the new telephone cable across Cook Strait. It came into use for examination of the two joints, the cable being laid in three sections and tho final splice taking place in midStraft. Unlike the ordinary telegraph submarine cable with its simple structure of a copper conductor, the coaxial has-a more intricate make-up. It contains a central conductor surrounded by fine copper tapes, and then heaviiy insulated with paragutta, upon which arc wound six copper strips. Where the old type of cable worked on a direct current the most modern type utilises high-frequency currents and thus, 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 teleprinter circuits for telegraphy. \\ hen the cable joints were made at sea the greatest care had to be taken in centring the conductor within its heavy insulation and also to properly wind the copper strips in relation to the core. Air bubbles bad to be avoided in the splice and a perfect adhesion of the various layers of insulating material was essential. Consequently, at intervals during the operation the X-ray machine came into use to give visual indications of the efficiency of this delicate splicing operation. Although this type of joint is quite new in the world, and extreme accuracy is required in its making, tho cable jointers, despite the unusual conditions, made a perfect job, as the Xray 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 month or six weeks, by means of specially designed electrical measuring apparatus in order to determine its electrical characteristics under the temperatures at the bottom of Cook Strait. The observers thus obtain data necessary for the proper adjustment of the H rrier terminal apparatus to be installed at Lyall Bay and Blind River, 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 the elaborate electrical measurements of the cable have been completed.