NEW COOK STRAIT CABLE

Press, Volume LXXIII, Issue 22244, 8 November 1937, Page 12

NEW COOK STRAIT CABLE

TELEPHONE SERVICE IMPROVED

BIG UNDERTAKING COMPLETED

The coaxial coble recently laid across Cook Strait from Lyall Bay, Wellington, to Blind river, Marlborough, is now in use, and by supplementing the channels provided in the old cables, is giving seven direct circuits to Christchurch, and three to the Blenheim and Nelson districts. Crossstrait telephone communication is an important feature of the Post Office telephone business, the average number of conversations each month being 17,500. Installing and adjusting the complicated terminal equipment is almost as heavy an undertaking as the laying of the cable itseii. Electrical currents of frequencies above the audible range are utilised lor transmitting speech over the cable, the range of irequencies being Irom six to 60 kilocycles a second. To transmit speech over the new cable involves a complicated electrical operation, which, however, is done quite automatically by the Britishmade equipment now being installed o. both sides of Cook Strait. A new repeater station has been built at Lyall Bay, where the normal speech currents are converted into high frequency impulses for transmission to the South Island, while speech from the south has to be demodulated or converted into the range of audible frequencies used on subscribers' telephone lines.

High Pitched Sounds If it were possible to listen in to tha traffic on the submarine cable, all that could be heard would be a pulsating series of high-pitched musical sounds, to which the nearest parallel in nature is the twittering of small birds. On the longest waves used in this traffic these sounds could be heard by many people, though speech would be unintelligible, but as the upper limit of the frequency range is approached, there is no sound audible to the human ear In this form speech between Wellington and Christchurch passes over cable and land lines, to be converted at the terminal points into audible frequencies for transmission to subscribers.

Lyall Bay repeater station, replacing the modest wooden cable hut which did duty for many years, is a welldesigned concrete building 66 feet long, with a spacious room to accommodate the delicate electrical apparatus for the high frequency telephone channels. This apparatus is mounted on panels 10 feet high, and there is space for considerable extension as more and more of this equipment comes into use to meet the growing needs of long-distance telephone business.

Commercial operation of the new cable was preceded by a long series of electrical measurements, an essential preliminary to accurate adjustment of the terminal equipment. An interesting electrical feature of the coaxial cable is that the transmission losses over its length of 40 nautical miles are equivalent to those experienced over 200 miles of the standard type of open aerial line. Temperature is another factor which has to be taken into account by the engineers, who have found that the average temperature of the bottom of Cook Strait is 50 degrees Fahrenheit, and that it is almost uniform throughout the year. Wellington's mean temperature over the year is 54.8 degrees.