ACROSS THE STRAIT

Dominion, Volume 14, Issue 299, 12 September 1921, Page 7

ACROSS THE STRAIT

PROBLEM OF TELEPHONE COMMUNICATION WIRELESS IS PRACTICABLE - THE CHIEF ENGINEER’S REPORT "There are two mediums by which a toll telephone service can be established between tho North Island and the South Island, says the Chief Telegraph Engineer (Mr. E. A. Shrimpton), in tho report on his recent visit to Europe and America. I'These are, (1) submarine cable, (2) wireless. If such a service is opened to the public, at least three channels must be available—i.e., provision msde for three pairs of persons to hold simultaneous conversations. ~ Submarine Cable. To meet this provision a submarine cable will require to have four continuously loaded conductors, giving two metallic circuits, and a phantom circuit superimposed. The only country making such a cable at present is Great Britain. The cable would weigh from wO to 1000 tons, and would have io be brought to New Zealand and laid by a special ship—i.e.. a cable ship, lhe cost of the cable, including the cost or freight, laying, cable huts, and land l..ne from huts at each side of the stmt to Wellington and Blenheim .respectively would be quite 12100,000. In tho Absence of trunk lines from Blenheim to Christchurch, the cable would serve only Marlborough and Nelson in the South Island. The cost of erecting the necessary trunks from Blenheim to Christchurch, and strengthening tho existing poles to cairy the extra wires, is estimated to cost £28,000; therefore, before Wellington and other ceptres in the North Island Could have telephonic talks to the chief centres in the South Island it would _yvolve the country in.fin expenditure of Aiio,000. I have considered the tact tt.at Christchurch has telephone racilities to ’and from Dunedin, but the trunk circuits between these places are already quite loaded, and if they are asked to carry additional traffic it could only be done with a large delay—in other words, the waiting time may run nito two oi three hours durins’ the height of tho daily busy hours. I Wireless.. ! "Catalina Island, lying about fertyfiva miles off the Californian coast, has a threo-ohannel wireless telephone serI vice to Loe Angeles, and provision is made for repeating the wirelesA speech over the wire system to practically any place in the United States. VTlio average daily traffic to and from Catalina is I.W messages. The wireless speech is remarkably clear, and comparatively great in volume. I heard speech passing ito rnd from Catalina at Los Angeles, and when at San Francisco I spoke to Catalina over a,circuit made up of over 800 miles of trunk line to Los Angeles and thence, by wireless. The speech was perfectly articulated, without any attenuation. "As far as the toll operators at Los Angeles are concerned, they have three physical circuits, which are operated in the same manner as a wire circuit. Ringing and speaking keys are used exactly the same for wireless as tor Hired circuits.* When Ids Angeles toll operator presses a ringing key it drops a shutter at Catalina the same as if it were a wire circuit. Pressing the ringing key sends the ringing current of ordinary telephone ringing frequency through a relay at the aerial, which in turn places voice frequency ringing on to the aerial. This at Catalina, on a valve amplifying set causes, sufficient energy to pass through an indicator cou to operate it. Of course, any licensed amateur,' or a ship’s wireless operator equipped with a valve receiver and booing coils, can tap wireless telephone speech; secrecy, therefore, by the nature of things, is impossible. Z "Hitherto it has been generally ac“c ep ted that there is a large amount of interference caused to wireless telegraph stations'’working on wave length# near that of wifeless telephony, and ferj that reason it was considered that the use oi wireless telephony probaldy be confined to cases where wire telephony cannot be used, such as transoceanic communications, communications with aircraft, or very long land lines where maintenance would be difficult or impossible. When I was in j-ondon the Marconi Company was conducting experiments with wireless telephony with speech superimposed on 3500 metres wave length, and were stopped, excepting for a few houfs hfter midnight, On account of | the. interference their experiments caused with communications to an craft working on 900 metres wave length. In spite of this there is a wireless telegraph station quite close to the tele.phone aerial ■on Catalina Island, and I am informed no interference at all is experienced. A Practical Proposition. "From whatl I saw and heard in the United States, I feel confident that wireless telephony will provide a . practical proposition for opening up inter-island telephone service. Tho cost of a threechannel wireless installation, including the aerials and repeating apparatus, is estimated to be a tenth of the cost of 'a submarine cable'giving equal facilities —i.e., about £IO,ODO. It is a difficult matter to compare! the annual maintenance Charges of the respective systems, because the maintenance of the cable is an unknown quantity, but tho cost of repairing one break in the cable would equal many years’ 'maintenance of the wireless equipment. “The estimated cost for the wireless telephone equipment given above is for a three-chaniiel service from Wellington and Blenheim, with' repeating facilities tor intercommunication between the wire and wireless systems. Wireless equipment giving two channels each to Christchurch and Blenheim from Wellington should not cost more'than an additional .£2OOO. The Department has suitable land at Lyall Bay and New Brighton for the erection oLivireless aerials; Dio Blenheim aerials could be erected otor the chief post office building. “The American Telephone and Telegraph Company is laying’ what I shall call 'mystery cables’ from Key W est to Cuba. These cables are to provide telephone and telegraph facilities, and arc not metallic for the whole of the distance —about ana hundred miles—but have an uninsulated return for the greater portion of their lengths. The insulated portion is continuously loaded. The cables are being manufactured in England, and tho first one was expected to be laid in February. What the American Telephone and Telegraph Company expects to get out of these cables has not been disclosed by its engineers; indeed, from what I heard in America I believe exactly what facilities those extraordinary cables will provide is really unknown, and will only be determined after they are laid and tried out. I certainly would recommend deferring consideration of laying a submarine telephono cable across Cook Strait until tho result of these Cuban cables is known. The cost of such cables will be considerably less than the class of cables usually considered essential for telephone purposes under such waters aa in the strait. The cost of materials is coming down, co we have everything to gain in delaying the consideration for a submarine "Specifications are being prepared for n three or four-channel wireless telephone installation for working from Wellington to Blenheim and Christchurch, and when these are ready they will be submitted to one or-two companies specialising in such equipment. The results will be communicated to the Minister with a recommendation."