1222 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



was then under development by the Research Department of the Western 

 Electric Company, and which later on became widely known as permalloy .^^ 



Key West-Havana Submarine Telephone Cable System 



This project required three different submarine cables ranging in length 

 from about 100 to 105 nautical miles, each being a great deal longer than 

 any previously designed for telephone transmission, and a large fraction of 

 the route was in deep water, reaching a maximum depth somewhat over 

 6000 ft. The difficulties to be expected in protecting loading coils from injury 

 under the great hydrostatic pressure involved, and the complications that 

 would be encountered during installation and in subsequent maintenance 

 work, prevented coil loading from receiving consideration. Moreover, the 

 great water pressure also eliminated consideration of paper insulated cable. 



Since the cables were intended for use in telephone circuits connecting 

 remote points in the United States with Havana and remote points in Cuba, 

 the over-all system design requirements were very formidable. In addition 

 to a two-way telephone circuit in each cable, provision also was made for 

 three carrier telegraph circuits above the voice range, and for direct current 

 grounded telegraphy below the voice. These complex requirements brought 

 in difficult problems regarding telegraph flutter interference and other types 

 of non-linear distortion. 



The fundamental design studies resulted in a decision to install single 

 core, continuously loaded, cables using gutta-percha insulation, and having 

 a concentric system of copper tapes wrapped around the insulated conductor, 

 for use as a return conductor. (These cables were the first to be installed 

 with this feature.) Iron-wire type continuous loading was chosen largely 

 because the desired project in-service dates did not allow sufficient time for 

 the additional research and development work, and the additional manu- 

 facturing preparations, that would have been necessary in order to use 

 permalloy tape loading. The manufacturing situation presented serious 

 problems, because it was necessary to plan for manufacture abroad, since no 

 American company had facilities for making deep-sea submarine cable. 

 Moreover, iron-wire type continuous loading (as proposed by C. E. Krarup* 

 of Denmark) was old in the European telephone art, having been used in 

 several short submarine cables, and some underground cables. 



In the Cuban Straits cables under discussion, the central copper conductor 

 had a diameter of about 0.140 inch. About this was closely wrapped a single 

 layer of 0.008 inch soft iron wire and three layers of gutta-percha type 

 insulation having a total thickness of about 0.135 inch. A thin copper tape 

 directly on this core furnished protection against damage by the teredo, 



*E.T.Z., April 17, 1902. 



