2 THE BELL SYSTEM TECHNICAL JOUllNAL, JANUARY 1957 



stranded copper conductor, insulated with gutta-percha and finished 

 off with servings of jute yarn and soft armoring wires — to the relatively 

 complex structure of the modern coaxial cable, strengthened by high 

 tensile steel armoring for deep sea operation. The coaxial structure of 

 the conducting path is necessary for the transmission of the wide fre- 

 quency band width required for many telephone channels of communi- 

 cation. The optimum mechanical design of the structure for this first 

 transoceanic telephone cable has been determined by many experiments 

 in the laboratory and at sea. As a result, the cable engineer is confident 

 that the risk of damage is exceedingly small even when the cable has 

 to be laid and recovered under conditions which impose tensile loads 

 approaching the breaking strength of the structure. 



The great difference between the transatlantic telephone cable and 

 all earlier transoceanic telegraph cables is, however, the inclusion of 

 submerged repeaters as an integral part of the cable at equally spaced 

 intervals and the use of two separate cables in the long intercontinental 

 section to provide a separate transmission path for each direction. The 

 repeaters make possible a very large increase in the frequency band 

 width that can be transmitted. There are fifty-one of these submerged 

 repeaters in each of the two cables connecting Clarenville in Newfound- 

 land with Oban in Scotland. Each repeater provides 65 db of amplifi- 

 cation at 164 kc, the highest transmitted frequency. The working 

 frequency range of 144 kc will provide thirty-five telephone channels 

 in each cable and one channel to be used for telegraph traffic between 

 the United Kingdom and Canada. Each cable is a one-way traffic lane, 

 all the "go" channels being in one cable and all the "return" in the 

 other. 



The design of the repeaters used in the North Atlantic is based on 

 the use of electron tubes and other components, initially constructed 

 or selected for reliability in service, supported by many j^ears of research 

 at Bell Telephone Laboratories. Nevertheless, the use of so many re- 

 peaters in one cable at the bottom of the ocean has been a bold step 

 forward, well beyond anj^thing that has been attempted hitherto. There 

 are some 300 electron tubes and 6,000 other components in the sub- 

 merged repeaters of the system. Many of the repeaters are at depths 

 exceeding 2,000 fathoms (2j miles) and recovery of the cable and re- 

 placement of a faulty repeater might well be a protracted and expensive 

 operation. This has provided the incentive for a design that provides a 

 new order of reliability and long life. 



On the North Atlantic section of the route, the repeater elements are 

 housed in flexible containers that can pass around the normal cable 



