The Picturephone System: Mastergroup Digital Transmission on Modern Coaxial Systems
01 February 1971
The introduction of intercity Picturephone service will stimulate growth in the amount of digital information requiring transmission over long distances. It is important to provide for this growth and for the increasing capacity required for high-speed data in an evolutionary manner. This has motivated the development of terminal equipment to adapt existing microwave radio 1 and analog coaxial facilities for the transmission of digital signals. The L-4 coaxial line is an excellent medium for an efficient hybrid transmission system.2 A high signal-to-noise ratio (S/N), excellent linearity, and well-defined and stable transmission characteristics make it very attractive for multilevel pulse transmission. A mastergroup band provides a convenient subdivision for frequency multiplexing high-speed digital and analog signals. The mastergroup band has a bandwidth of 2.52 MHz and conventionally provides for 600 frequency division multiplexed voice channels. A mastergroup band is also capable of carrying two time-division multiplexed 6.312-Mb/s signals and, thus, can handle two digitalized Picturephone signals. It is planned that the digital mastergroup signals will be transmitted over the L-5 coaxial system that is currently under development. 501