SG Undersea Cable System: Repeater and Equalizer Design and Manufacture

Exploratory work on undersea amplifiers and devices in the late 1960s produced models of repeaters with the performance required for a 3500-channel, 4000-nmi system with a top frequency of 27.5 MHz. The specific development of the 30-MHz, 4000-channel, SG system was started early in 1971. The first SG installation, TAT-6, which connects Green Hill, R.I., with St. Hilaire, France, was completed in July 1976, yielding 4200 channels. The fivefold increase in bandwidth of SG over SF1 was made technically possible by advances in the design of reliable, ultralinear, silicon microwave transistors.6 Manufacturing the necessary numbers of undersea bodies economically and on schedule required substantial innovations in the basic mechanical construction and assembly techniques of the electronic units. 2355 II. GENERAL OBJECTIVES 2.1 Noise and load The SC. system was designed to meet the international objectives of 1 pWpO/km (38.6 dBrncO for 3500 nmi), average, with a signal load of -- 13 dBmO per 3-kHz spaced channel. The "worst channel" could be 2 pWpO/km. Once the noise, load, channel capacity, and cable diameter are specified, and the achievable amplifier noise figure and modulation coefficients are known, the repeater gain (and spacing) can be determined from the following approximate relationship: s/n = - 1 . 8 - ^ [ m a + b - c + 10 logCrip + 20 log(n) J - ^ 1 0 l o g ( K T B ) + N F + G R + 1 0 log(n) J ,