19-i THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



conductor and thus completed the coaxial structure. The dimensions of 

 these tapes were precisely controlled. The helical structure was chosen 

 to impart flexibility to the coaxial. 



Insulation of some of the early submarine telegraph cables suffered 

 from attack b}^ marine borers such as the teredo, pholads and limnoria. 

 To protect against such attack, a thin metallic tape was placed over the 

 insulation in the early submarine cables. The necessity for such protec- 

 tion for the transatlantic cables, especially in deep water, may be ques- 

 tioned, but the moderate cost of this protection was considered cheap in- 

 surance against trouble. The copper teredo tape was applied directly 

 over the return conductor, as a helical serving Avith overlapped edges to 

 completely seal the coaxial from attack by all but the smallest marine 

 organisms. 



A cotton tape treated with rubber and asphaltum-tar compound was 

 applied over the teredo tape to impart mechanical stability to the co- 

 axial during manufacture. A small gap between adjacent turns of the 

 helix was specified to permit ready access of water to the return tape 

 structure and to the surface of the core. The use of a gap was based on 

 laboratory tests which showed that transmission loss was dependent to 

 a modest extent on thorough wetting of the exterior of the coaxial. Since 

 transmission loss measurements are made on repeater sections of cable 

 shortly after manufacture to determine whether any length adjustments 

 are required, it was essential that the wetting action be as rapid as 

 possible. 



The design of the protection and strength components of the cable was 

 modified according to the depth of the water in which the cable was to 

 be laid. To prevent damage to the coaxial by any cutting action of the 

 armor wires during manufacture and laying, a resilient cushion of jute 

 roving was placed between the armor wires and coaxial. For type-D 

 cable, a single layer of jute was used; for types A and B cable, the bed- 

 ding was made up of two layers of jute. To protect this jute from micro- 

 biological attack, a cutching treatment was employed. The traditional 



Table I 



