III. ELECTRICAL CHARACTERISTICS OF ELECTRO-MECHANICAL 

 SUBMARINE CABLES 



From the standpoint of electrical characteristics, there are at 

 least three basic types of E-M cable: the coaxial cable, the multi- 

 conductor cable, and the single-conductor high-voltage/ampacitv power 

 cable. There is no one-to-one correspondence between application types 

 and electrical types since E-M cables include all three electrical 

 types, with the majority being either coaxial or single-conductor types. 

 Suspended E-M cables, i.e., load-bearing cables suspended in the water 

 column vertically, horizontally and anywhere between, include mainly 

 coaxial and multi-conductor types. The high-power single-conductor type 

 of cable is virtually excluded from water column E-M cables because there 

 is, at present, no requirement for such cables, since the transfer of 

 large amounts of power is limited almost entirely to land. 



The most versatile signal-transmission cable is the coaxial type. 

 The coaxial signal cable, as far as miles laid on the seafloor, far out- 

 ranks the bottom-lying single-conductor power cable. In addition, prac- 

 tical types of E-M coaxial cable (i.e., having physical dimensions and 

 mechanical characteristics which allow raising and lowering to deep ocean 

 depths) can also carry power on the order of 100 KW simultaneously with 

 high-frequency signals (bandwidth around 100 MHz). Because of the geo- 

 metry of concentric conductors, the coaxial cable generally has better 

 high-frequency characteristics than a multi-conductor or twisted-quad 

 cable. 



The signal-transmission characteristics of drv- jacket coaxial cable 

 and dry-core shielded multi-conductor cable are not, in general, affected 

 by the presence or absence of external armor, except insofar as the armor 

 may prevent certain adverse mechanical effects such as axial twisting, 

 small-radius bending, or physical damage to the jacketing material. E-M 

 cables having an internal strength member concentric with a central con- 

 ductor will, of course, have their electrical properties affected in that 

 the low frequency (<100 Hz) resistance of the conductor is increased by 

 the substitution of steel for copper. 



Conductor Materials 



Copper . Soft annealed copper (electrolytic, 99.09 percent pure) is 

 used in the conducting members of the vast majority of E-M cables of the 

 coaxial and multi-conductor types. Seafloor cables which are used pri- 

 marily for multi-channel signal transmission also use copper in the con- 

 ducting members. If the insulating materials has constituents, e.g., 

 sulfur, which have corrosive effects on copper, the copper is coated with 

 a thin layer of another metal or alloy; tin or lead/tin is commonly used 

 for this purpose. 



The main reasons for using copper in marine coaxial E-M cables is 

 that these cables are used primarily for signal transmission, and copper 

 provides the best combination of low cost and high conductivity — the 

 latter being essential for maximum frequency bandwidth. In bottom-laid 

 coaxial telephone cable, oxygen-free copper is used in the central con- 

 ductor. Because a welded seam exists in this conductor, it is essential 



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