Repeaters and Equalizers for the SD Submarine Cable System

T h e decision to replace the flexible repeater of the SB submarine cable system 1 with a rigid structure of more conventional length-todiameter ratio permitted the design of a repeater of increased bandwidth with equivalent four-wire operation. T h e objectives relating to stability and reliability remained the same as for the SB repeater. In the design of repeaters for submarine cable systems, attention must be paid to the smallest detail, and long testing programs are required to realize the stability and reliability objectives. Generally, basic circuit and mechanical concepts are well proven, but must be refined to an extremely high order of perfection to meet the system transmission and life requirements. T h e SD system 2 for which this new repeater was designed operates over a frequency range of 108-">04 kc (low band) and (560-1052 kc (high band). The repeaters are spaced at 20-nautical mile (nm) intervals. T h e repeater gain matches the cable section loss within + 0 . 3 0 or --0.10 db in the low band and ± 0 . 1 0 in the high band. Excess gain or loss of a repeater section is called misalignment. To avoid a substantial buildup of misalignment, equalizers are inserted every 10 repeater sections. This keeps the misalignment down to ± 0 . 2 0 db per 192 nm. T h e equalizers also compensate cable loss changes t h a t occur during laying. For this 1243