characteristic impedance is important in establishing design criteria 

 for splicing coaxial cable. In general, an impedance or admittance dis- 

 continuity in a signal transmission cable will cause reflection of 

 energy and, hence, loss. 



In the case of relatively short-distance E-M. cables (surface-to- 

 bottom types) reasonable care in soldering/welding electrical conductors 

 and molding/extruding the dielectric will insure that signal losses are 

 under 1 percent. Only the grossest negligence in splicing will cause 

 reflection losses to approach 50 percent. An inexperienced (but still 

 conscientious) splicer could, by soldering on improperly cleaned surfaces 

 or at too low a temperature, produce a 2-ohm series resistance in the 

 central conductor of the coaxial cable. A large admittance could be 

 generated by allowing a thin disc-shaped pocket to remain in the 

 dielectric and fill with seawater. 



In the manufacture of S-series submarine telephone cable it some- 

 times becomes necessary to splice the armorless coaxial line because of 

 damage in the central conductor. Copper-plated sleeves, more than twice 

 the diameter of the central conductor, are inserted at points where the 

 strand in the central strength member may have been damaged or where more 

 than 2 inches of copper is missing. Since these repairs constitute poten- 

 tial weak points in the cable and produce a certain amount of signal re- 

 flection (although well below 1 percent), not more than two splices are 

 permitted within any 20-nautical mile section of cable. Restoration of 

 the polyethylene dielectric is done by extrusion molding. The completed 

 joint is x-rayed to check for inclusions, voids, and eccentricity. 



For most of its length a deep-ocean S-series coaxial telephone cable 

 does not have to be shielded against external signals and noise. How- 

 ever, on passing through shallow water at the shore ends, electrical 

 shielding is provided in the form of high-permeability steel tape and, 

 as discussed elsewhere in this report, various types of armoring are also 

 provided. Shields of high-permeability steel tape actually function as 

 magnetic shields and reduce the inductive coupling to the internal con- 

 ductors. The magnetic shield diverts the disturbing field around the 

 conductors by providing a low- reluctant path; also, eddy currents are set 

 up in the shield which generate opposing fields to the external field. 



The latest S-series submarine cable to be manufactured in large 

 quantity is the SF cable. 21 > 22 it h as a larger dielectric O.D. than the 

 SD cable which, in turn, yields a bandwidth about six times that of the 

 SD cable. Table III-4 lists the pertinent physical, electrical, and 

 system characteristics of the SB, SD , and SF cables. As of this writing, 

 the SG cable is on the drawing board. 



Multi-Conductor Cables . Multi-conductor E-M cables are used for 

 instrumentation, control, and signal transmission. A control and instru- 

 mentation cable may have as many as 59 separate conductors contained 

 within a circular cross-section area of 1.6 inches diameter. A cable of 

 this type would be capable of carrying voltages up to about 500 volts 

 between single-wire conductors and up to about 1000 volts on separate 

 coaxial cables contained in the same 1.6-inch diameter area. These small 

 diameter coaxial cables have larger resistance and capacitance per foot 

 than coaxial ocean telephone cables and, hence, larger attenuation. 



30 



