The SD Submarine Cable System

In 1954, before the installation of the first transatlantic telephone cable, growth studies had shown that submarine cable systems carrying many more channels than the systems then under development would be required to carry future traffic. The development of these wider-band systems was therefore initiated before the development of the SB submarine cable system1 was complete. Exploratory studies indicated that a new approach to cable and repeater design would be required. The SB system used armored coaxial cables, one for each direction of transmission. The repeaters were long and flexible so they could be handled on shipboard without major modifications to the cable machinery, which 1155 1156 T H E BELL SYSTEM TECHNICAL J O U R N A L , JULY 1964 had been developed to lay submarine telegraph systems. While these long, flexible repeaters have proven to be sound in concept and reliable in performance, the form factor is such as to introduce large parasitic inductance and capacitance in the interconnections between the stages of the repeater and in the feedback path from input to output. In consequence, it is not possible to design a wideband repeater using this mechanical approach. For the new broader-band systems, therefore, the repeater circuit was placed in a rigid cylindrical container. The cable concept was changed, and the strength was placed in the center of the cable rather than in the armor wires on the outside. Such construction makes possible a cable with a very stable transmission characteristic and eliminates the tendency of the cable to untwist under tension.