A SUBMARINE TELEPHONE CABLE WITH SUBMERGED REPEATERS 67 



conductors for alternating currents, and this makes the resistance of the 

 return path rise to undesirable values. The copper return effectively removes 

 the armor wire and sea water from the transmission circuit at all but very- 

 low frequencies. This has the further advantage of reducing the exposure of 

 the circuit to static noise. 



Although the iron wire loading was very effective in reducing attenuation 

 in the voice range, the eddy current resistance due to the loading wire made 

 itself felt to a rapidly increasing degree for frequencies above the voice band. 

 Consequently, when additional circuits were required some years later and it 

 was decided to extend the frequency range in order to make use of newly 

 developed carrier frequency equipment, it was necessary to dispense with 

 magnetic loading. In 1930 the Key West-Havana No. 4 cable was laid em- 

 bodying new materials and novel principles of design.^ The insulating ma- 

 terial in this case was paragutta, which had been recently developed by the 

 Laboratories, and which possessed electrical characteristics and stability 

 much superior to gutta-percha. An intensive study had been made of the 

 design of coaxial cables for carrier frequencies with the aim of obtaining 

 optimum electrical performance by proper proportioning and construction of 

 the conductors and these principles were employed in the new cable. Initi- 

 ally, three carrier telephone circuits were obtained on the No. 4 cable using 

 the equivalent four-wire method, with separate frequency bands for trans- 

 mission in opposite directions. The cable had been designed with considerable 

 transmission margin and in 1940 the need for additional circuits to Cuba 

 resulted in the installation of new terminal equipment which enabled it to 

 provide seven two-way high quality circuits on an equivalent four-wire basis. 



The Key West-Havana No. 4 cable design has proved very popular in 

 other parts of the world. Several such cables have been laid between England 

 and the Continent and between England and Ireland, between Australia 

 and Tasmania, and others were used in connection with the war effort. A 

 cable of this design has also been laid between two of the Japanese islands. 



Submerged Repeaters 



The demands for circuits to Havana continued to grow, and, after the 

 close of World War II, the time appeared ripe for making use of a new 

 development which had just come to a head in the Laboratories after a 

 period of experimentation.^ This development was the submerged repeater. 

 The need for periodic strengthening of signals transmitted over con- 

 siderable distances is about the same in submarine cables as it is in land 



m. A. Affel, W. S. Gorton, R. W. Chesnut, New Key West-Havana Carrier Telephone 

 Cable, B.S.TJ., Vol. 11, pp. 197-212, April 1932. 



^O. E. Buckley, The Future of Transoceanic Telephony, Thirty-Third Kelvin Lecture, 

 B.S.TJ., Vol. 21, pp. 1-19, July 1942. 



