OVER THE STRAIT

Evening Post, Volume CII, Issue 62, 10 September 1921, Page 5

OVER THE STRAIT

INTER-ISLAND SPEECH

' TWO SYSTEMS DISCUSSED

WIRELESS TELEPHONY PRACTICABLE. ,

Reporting to the Postmaster-General (the Hon. J. G. Coates) on his recent visit to Europe and America, the Chief Telegraph Engineer (Mr. A. E!'Shrimpton) discusses the subject of telephonic communication between the North and South' Island. Hp expresses the 6pinion that wireless telephony will provide a practical proposition for opening up an inter-Island telephone service. "There are two mediums by which a toll service can be established between the North and South Islands," says Mr.. Shrimp ton. "These are: (1) Submarine . cable; (2) wireless,'., If "such", 4, service is opened to the public, at least three channels must be available—i.e., provision made, 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 circuite, and-a phantom-circuit superimposed. The only_ country making such a, cable at present.'.is jGreat'Britain.. . The cable would -weigh-' from"800'to 1000 tons, and would have to be brought to New Zealand and laid by a special ship—i.e., a cable ship. The cost of the •cable, including the'cost ot freight, lay-" ing; cable-huts, and land lines from huts at each side of the etrait to Wellington^ and Blenheim respectively would be quite £100,000. ■ In the absence of trunk lines from. Blenheim to Christchurchl, the cable would serve only Marlbbrough. and Nelson in the South Island. The cost of erecting the necessary trunks from Blenheim to Christ-church,/and strengthening the existing poles to.carry the extra wires, is estimated to cost £26,000; therefore, before Wellington and other centres in the-North Island could have telephone talks to the chief centres,in the South Island. it would involve - vthe country. in, an expenditure- of, £126,000. I have considered«,tlie fact that Christchurch has telephone facilities,'to and from Dunedin, but the trunk circuits between these places arc already quite loaded, and if thej are asked to carry additional traffic it could only be done ■with a large delay—in other words, the waiting-tiirte may run into two oi three hours during the height of the daily busy hours. WHAT WIRELESS DOES. "CaitaEna Island, lying about fortyfive miles off • the CaJifornian coast, haa a three-channel- wireless telephone service to Los Angeles, and. provision is made for repeating the wireless speech. over the wire system to practically any iplace., in' the United ■ States. The. average daily traffic to and-from Gatalina Je 150 messages.' The wireless speech is remarkably clear, and. comparatively gfeat in volume. I heard speech passing to and from Catalina at Los Angeles, and whan at San Francisco I spoke to Catalina over t- circuit made up of over 800-miles of trunk line to Los Angeles and thence by wireless. The speeoh 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 for -wired circuits. : When Los 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 telephoneringing 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 coil to operate it. Of course, any licensed amateur, or a ship's wireless operator equipped with a valve receiver and tuning-coils, can tap wireless telephone speech; secrecy, therefore, by the nature of things is impossible. "Hitherto it has been generally accepted that there is ■ a large amount of interference caused to wireless-telegraph stations, working on wave-lengths near that of wireless telephony, and for that reason it was considered that the use of wireless telephony would probably be confined to cases where wire telephony cannot be nged, such as trans-oceahic communications, communications with aircraft, or very long land lines where maintenance would be difficult or impossible. When I was in London the Marconie Company was^conducting experiments with wireless telephony with speech superimposed on 3500 - metres wave-length, and were.'stopped, excepting for -a few hours after midnight, on account of the interference their experiments caused with communications to aircraft working on 900 metres wavelength. In spite.of this there-is/a- wire-less-telegraph station quite close to the telephone'aerial on Catalina1 Island, and I am informed no. interference at all is experienced. „,,,,,. .„.,:„.'„'..,,',;;.,..',,'-7,1. ' advantage'in'cost.;-;;;": " FronV what 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. The 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 £10,000. 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 the 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-channel service from Wellington and Blenheim, with repeating facilities for 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 £2000. The Department .has suitable land at Lyall Bay . and New Brighton for the erection of wireless aerials; the Blenheim aerial* could be erected over the Chief Post Office build- ™ "The American Telephone and Telegraph Company is laying; what I shall' call "mystery cables" fro-m Key West to Cuba.. These cables ara/to provide telephone and telegraph facilities, and. are not metallic for the whole of the distance —about one hundred miles; —but have an uninsulated return for the greater portion of their lengths. The insulated portion, is -continuously loadedl. The cables are ; being manufactured' in England; and the first one was expected to l>e kid in February. What the American Telephone and Telegraph Company expects to get out of these cables nar not been disclosed by its engineers; indeed, from what I heard in America., I believe exactly what facilities these extraordinary cables will provide is really unknown, and will only be dtetermined' after they a-re laid andi tried out. "I certainly would "recommend deferring consideration of laying a submarine-tele-phone 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 as in the. Strait. The cost of materials is coming down, so yrt> have everything to gain in delaying the consideration for a submarine cable. ''Specifications are being prepared for ■ 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," ■ •