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Linearity and reproducibility of undersea electronics play key roles in determining the achievable performance of an undersea cable system. This paper describes the characteristics of undersea electronics and the measures taken in design and manufacture to achieve the desired performance and reliability, giving special emphasis to new features and applications. It describes in detail the performance achieved in the recently completed sg system linking the U.S. and France.

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Terminal transmission equipment has been developed for the SG cable system that, compared to similar equipment for land analog fa cilities, makes more efficient use of the transmitted bandwidth and provides superior continuity of service. Although economy of devel opment effort dictated the use of existing equipment and conventional design techniques wherever possible, many new designs were required to achieve the desired features. Means for protecting the undersea re peaters from gross signal overload and a carrier generating scheme for hypergroup and wideband-line frequency-translation equipment are examples of new designs that proved particularly challenging. Dupli cation of higher-level multiplex equipment coupled with automatic changeover switching is the means used to obtain the desired service continuity.In this regard, much care was required to limit amplitude and phase differences between duplicate transmission paths to insure "hitless" maintenance changeover switching. Other features of the terminal include an on-site equalizer design and construction capa bility at the wideband line and supergroup levels, a separate 3-channel order-wire facility, individual supergroup signal limiters, and the ability to operate with 3-kHz as well as 4-kHz/spaced message channels. Mechanical design follows the current French standard for such equipment.CIT-Alcatel in France carried out the detailed design.

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