NEW CABLE IN USE

Hawke's Bay Herald-Tribune, Volume 81, Issue 38, 8 November 1937, Page 8

NEW CABLE IN USE

Telephoning Across Cook Strait The coaxial cable recently laid across Cook Strait from Lyall Bay, Wellington, to Blind River, ^Marlborough, is now in'use, and by suppleihenting the channels provided in the old cables, is giving sevien direct circuits to Christchurch, and three to the Blenheim and Nelson districts. Cross-straight telcphone comxnunicatioh is an important feature of the post- office teiephone busi- j ness, the avetage number of conversa- j tiphs each- month being 17,500. It is a | business which has grown.rapidly, and is likely to extend with even. greater pace now that there 'is the equipment to cope with all possible demands, the coaxial cable having a potential capacity far beyond present requircments. Installing and adjusting the complicated terminal equipment is almost as heavy an undertaking as the laying of the cable itself. Electfieal. currehts of frcquencies above the aufiible fange are utilised for transmitting speech. over the cable, the range of frequencies being from six to sixty, kilocycles - per; second. To tran&mit speech - over the new cable involyes a complicated elec- • tical operation, which, hoWever,"is, done . quite automatically by tlie British rnade equipment now being installed on both sides of "Cook Strait., A new repeater station has been built at Lyall Bay where tho normal speech currents are converted into high frequency impulses for transinission to' the South ' Island, while speech from t,he south has to he demodulated or converted into thc range of audible frequencies used on subscribers' teiephone lines. If it were possible to listen in to thc 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 ds the twittering of small birds. On th« longest waves used in this traffic thesa sounds could be heard by mauy people, though speech would be unintelligible, but as the upper limit of the 'frequency fange is.appr'oached, there is-no sound, audible to the human ear. Ip. this form speech between -Wellington and Christchurch passes over cable and land lines, to be converted at "the terminal p'oints into audible frequencies. for trainsmission to subscribers. ; Another important feature of , iongdi'stance telephoning is that attentualion of the original volume of speech has ■, to be over come by amplification, aixd this is done, four times between the Wellington and Christchurch exchanges., Lyall Bay repeater station, replacing. the modest wooden cable hut which' didi duty for many years, is a well designed! concrete building 66 feet long, with ai spacious room to aecommodate the deli-j cate eleetrical apparatus for the highi frequency teiephone chaixnels. . This apparatus is mounted on panels 10 feet high* and .there. is space Tor considerable extension as more and more of this' equipment comes into use to meet the growing needs of long-distance teiephone business. Power ■ is taken from the ordinary source, but tp ensure absolutely smooth . working and freedom from voltage fluetu^tions, the Station operates from battery eurrenf, ' the batteries , having . sufficient storage capacity to run the system* for several days if there, is a bjeakdown in the ordinary supply of .current. Commercial operation of the new cable was .preceded by a long series of eleetrical measurements, an essential preliminary to accurate adjustment of the terminal equipment. An interesting eleetrical feature of the coaxial cable is that the transmission losses over its length of 40 nkutical miles are equivalent to those -experienced over 200 miles of thc 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 fahrenlxeit, and that it is almost uniform throughout the year. Wellingtons' mean temperature over tixe year is 54.8 degrees.