New Group and Supergroup Terminals for L Multiplex

The L multiplex terminals are used for Bell System long-haul telephone circuits, including those transmitted over the Ll and L3 coaxial systems, the TD-2, T H , T.I and TL microwave systems. Single-sideband amplitude modulation is used for translating voice channels into the broad frequency bands which can be transmitted by these systems. Several stages of modulation are required to form the complete baseband. As shown in Fig. I, these stages are known respectively as the channel bank, group bank, supergroup bank, and mastergroup bank. This paper describes a new design of the group and supergroup equipment. A companion paper 1 outlines the original development of telephone terminals for coaxial systems, their subsequent use on microwave radio systems, and the increasing need for better performance to accommodate new services such as direct distance dialing and data transmission. The development of channel banks including the new A5 channel bank is described in a recent paper. 2 The original development of the group and supergroup equipment was started more than 20 years ago.3 Since 223