History of the Atlantic Cable & Undersea Communications
1913 Anglo-Irish Cable
THE NEW ANGLO-IRISH TELEPHONE CABLE
The new Irish telephone cable, which is to serve the main trunk route between the southern half of the United Kingdom and Ireland, is the longest submarine loaded cable yet laid by the Department. Its total length is approximately sixty-four nautical miles, being thus some sixteen nautical miles longer than the Anglo-Belgian cable, which was laid in 1911. In several respects the two cables are similar in construction; the dielectric in each consists of the specially treated gutta-percha patented by Messrs. Siemens. They are both loaded on the transformer and phantom circuits, with coils spaced one nautical mile apart; the 7-wire copper strand forming each of the four conductors weighs 160 lbs. per nautical mile, and the dielectric 150 lbs. in both cases. The over-all weight of the completed cable is some 121 tons per nautical mile. Where the coils come in, the cable is strengthened by extra sheathing for about 92 feet. The following are the particulars:
A special feature of this cable is the provision of a fifth core of 50 mils copper G.P. insulated, which runs in the centre for half a naut. at each end of the cable. It is then brought out by means of an insulated iron strand, which is bound in and soldered to the sheath. This wire has been provided as an earth wire in connection with experiments on single-wire submarine telephone cables which are at present being conducted. The object of the length of half a naut. is to permit of the earth wire being taken out to sea and soldered to the sheath, so as to avoid the inductive disturbance which is generally found, to a greater or less extent, when earths are made in a cable hut, especially when telegraph cables are terminated in the hut.
The value of the attenuation constant Beta was specified not to exceed .016 per naut. when the transformer circuits and superimposed circuit were tested with a sinusoidal electro-motive force, having a periodicity of 800 per second, applied directly to the end of the cable, and producing one milliampere at the sending end.
The results obtained on the completed cable were as follows. A “Franke” machine was used for the tests.
SECTION OF NEW ANGLO-IRISH TELEPHONE CABLE. FULL SIZE.
The transformer circuits (the two diagonal pairs) have thus a standard cable equivalent of approximately nine miles.
The efficiency of the coils is such that, when taken separately, the ratio of the effective resistance (R) to the inductance (L) in each
The constants of the completed cable per naut. loop are as follows.
Overhearing was specified on the completed cable between either of the transformer circuits and the superimposed circuit to be not greater than would be observed in direct speech over 65 miles of standard cable having a resistance of 88 ohms per mile loop and a wire-to-wire capacity of .054 microfarads. The figure of 65 miles was stipulated because a similar result was obtained in the Anglo-Belgian cable, and it was feared that a higher figure could not be guaranteed.
The copper conductors are of 100 per cent. conductivity to E.S.C. standard for annealed high-conductivity copper. The sheathing wires, fourteen in number (with an additional 3-wire strand to indicate that the cable is a loaded one, are made of the best selected ball furnaced “all wire” pig iron, specified to have a strength not less than 23 tons per square inch and well galvanised with zinc spelter. Experience has shown that iron of this type is less subject to corrosion than the homogeneous iron which was formerly used by the Post Office.
Each completed set of loading coils, with their insulated covering and before jointing into the cable, was subjected to an external hydraulic pressure of 15 cwt. per square inch for not less than half an hour without producing distortion or other injury. The cable was constructed by Messrs. Siemens Bros. in their works at Charlton, Woolwich.
Aërial land lines of 600 lbs. copper have been run from the respective landing points to Manchester and to Dublin in order to secure a high standard of speech on the circuits. A description of the laying of the cable will appear in our next issue. J.G.H.
The Times December 30, 1913
The laying of the new telephone cable between Nevin, in Carnarvonshire, and Howth, near Dublin, a feat which has just been accomplished by the Post Office cable ship Monarch during heavy weather, has made a notable addition to the telephonic facilities between England and Ireland.
Until the present time the only cable available for telephonic traffic to Ireland has been that between Port Mora, near Portpatrick, and Donaghadee. This cable, which has been in service since 1893, is nearly 24 nautical miles in length, and is of the same type as that which was laid between Dover and Calais in 1891. Up to a comparatively recent date there were technical difficulties in the way of providing telephone cables except over narrow arms of the sea, like the Straits of Dover or the Stranraer-Larne route. The result has been that communication between England and Ireland was only possible over land lines through Carlisle, thence to Port Mora, by cable to Donaghadee, and south by land lines from Belfast.
During recent years the design of submarine telephone cables has improved to the point where it was found possible to lay one between St. Margaret's Bay and the coast of Belgium, and the successful working of that cable led to the decision to provide for direct telephonic communication with Dublin. The cable which, in pursuance of this policy, has now been put in service has a total lengtlh of 64 nautical miles (nearly 74 miles), and is the longest submarine telephone cable which has yet been laid. It was manufactured by Messrs. Siemens Brothers and Co., and is of the four-core Pupin-loaded design, this being the method by which satisfactory submarine transmission is made possible over any considerable mileage.
Last revised: 4 April, 2013