290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



on the transatlantic route will have a somewhat greater thickness of 

 insulation than that included in the makeup of the Key West-Havana 

 cable. The core diameter before the addition of the return coaxial 

 conductor will be 0.62 inch. Figure 6 illustrates the typical cross 

 sections used in different parts of the over-all cable system. It will be 

 noted that the interior structure, namely, the inside conductor, the 

 insulation, and coaxial return conductor are the same in each case, the 

 cables differing only in the degree to which external materials, includ- 

 ing armoring, are applied, depending on the location of the cable. 



Manufacture of the cable demands control of the dimensional 

 tolerances to a greater degree of precision than has been attempted 

 heretofore. This is because the large number of repeaters in the cir- 

 cuit make it of great importance to maintain a fine balance between 

 repeater amplification and cable loss. Predetermination of the effects 

 of temperature and pressure on cable attenuation assists in maintain- 

 ing this balance when the cable is at sea-bottom temperature and 

 pressure. Fortunately, the sea-bottom temperature is very constant. 

 Electrical irregularities which would result from structural imperfec- 

 tions must also be avoided since they affect the gain-frequency char- 

 acteristics of the repeaters. 



As is customary in cable practice, special cable armoring will be used 

 near the shore ends and the various types are shown in figure 6. Type 

 A has an armoring consisting of 12 galvanized mild-steel wires, each 

 0.3 inch in diameter, and is laid in water not deeper than 300 fathoms ; 

 type AA, used for some landings, is similar but has an extra layer of 

 armoring. Type B is laid in moderate depths and has 18 mild-steel 

 wires, each 0.165 inch in diameter. Type D is laid in all depths greater 

 than 700 fathoms. It is armored with 24 high-tensile steel wires, each 

 0.086 inch in diameter, each wire being taped ; these enable it to be laid 

 and lifted in the deepest water. 



The structure and dimensions of the conductors and core of the sub- 

 marine cable used between Clarenville and Sydney Mines will be iden- 

 tical with those of the cable used between Clarenville and Oban. The 

 cable will have AA- or B-type armoring. It will, however, be tested to 

 a specification appropriate to the higher frequencies to be transmitted. 



The land cable will be basically the same as the submarine cable but, 

 being more subject to electrical interference, will be shielded with lay- 

 ers of soft iron tape applied over the outer conductor. The tape in 

 turn will be protected from corrosion by a polythene sheath over which 

 will be applied jute bedding. 



The cable will be laid in a trench at a depth of approximately 30 

 inches where the temperature is expected to have an annual variation 

 of about 35° F. and a maximum daily variation of about 2° F. Guard 

 wires, for the protection of the system against lightning, will be laid in 



