SG Undersea Cable System: Cable and Coupling Design

As discussed in the preceding papers, the British Post Office (BPO) had primary responsibility for cable development for the SG system and Bell Telephone Laboratories (BTL) was responsible for the repeaterto-cable coupling design. A number of factors ruled out the use of 1.5-in. diameter-over-dielectric (DOD) SF1 cable for the SG system; not least of these was its high loss. The channel capacity chosen for SG required an upper frequency of approximately 30 MHz. At this frequency, the attenuation of SF cable for a transatlantic system would have reached a formidable 32,600 dB but, by using a low-loss dielectric at an increased diameter, 1.7 in. DOD SG cable reduced this total by 5000 dB. This saved 123 repeaters and reduced the system power feed voltage. However, cable attenuation remained far higher than on any previous system. This was reflected by: an increased sensitivity to manufacturing tolerances, significant attenuation changes with time (cable aging), and increased importance of laying effects and sea-bed temperature and 2435