100 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



At the shallow water shore ends, the armor types are characterized by 

 the use of mild steel wires which are increased in diameter in steps as 

 the landing is approached. These types are designated A and B and will 

 be described in greater detail later. 



The transmission loss of this cable structure at the top operating fre- 

 quency of 164 kc is 1.6 db per nautical mile and is 0.6 db per nautical 

 mile at 20 kc, which is the lower end of the frequency band. The high 

 frequency impedance of the cable is about 54 ohms. 



BASIS OF DESIGN 



A coaxial structure was first used for telephone and telegraph service 

 in a submarine installation in 1921, between Key West and Havana, 

 Cuba. Three coaxial cables with continuous magnetic loading and no 

 submerged repeaters were laid. One telephone circuit and two telegraph 

 circuits were provided in each cable for each direction of transmission. 



In 1950, a pair of submarine coaxial cables,^ which included flexible 

 submerged repeaters, was laid between Key West and Havana, Cuba. 

 Each cable furnished 24 voice circuits. One cable served as the "go" and 

 the other as the "return" for the telephone conversations. The transat- 

 lantic telephone cable design is similar to this cable except that the 

 nominal diameter of the insulation is 0.620" instead of 0.460". An out- 

 standing difference between the transatlantic and Key West-Havana 

 systems is cable length — about 2,000 nautical miles as compared with 

 125. This difference influenced significantly the permissible electrical 

 and mechanical tolerances applying to the cable structure. 



The installation of some 1,200 miles of cable with island based re- 

 peaters for a communication and data transmission system for the U. S. 

 Air Force, between Florida and Puerto Rico,^ followed the 1950 sub- 

 marine cable system. The design of this cable is identical with that of 

 the transatlantic cable, except for differences in the permissible dimen- 

 sional tolerances on the components of the electrical transmission path. 

 Data obtained on the electrical performance of the Air Force cable pro- 

 vided the transmission characteristic to which the repeaters for the 

 transatlantic project were designed. 



The design of this cable installation was the result of many years 

 of cable development effort, which was guided by the successes and 

 failures of the earlier submarine telegraph cables. The 1950 Key 

 West-Havana and the Air Force cables differed from the earlier struc- 

 tures in one important respect, namely, the lay of the major components. 

 A series of fundamental design studies during the 1930's and 1940's and 

 extensive field tests in the Bahamas in 1948 demonstrated that having 



