A Carrier Telegraph System for Short-Haul Applications

Most short Bell System telegraph circuits, particularly those in the less-densely populated areas of the country, have customarily been operated over direct-current facilities obtained by compositing or simplexing physical telephone circuits. Many of these extend from a telegraph repeater in a central office to another arranged as a subscriber set and mounted in the knee-well of the customer's teletypewriter table. Thus, for example, circuits are extended to Teletypewriter Exchange Service (TWX) subscribers located far from the switchboard. The T W X facilities are arranged to handle supervision as well as transmission. The form of supervision is identical to that obtained when local facilities are employed and hence uniform operating procedures are obtained at TWX switchboards for all subscriber stations without regard to their geographical location. During and immediately following World War II, the growth of the Bell System's telegraph business resulted in some shortage of dc facilities. It. was foreseen that this shortage would be rapidly intensified by the use of new short-haul carrier telephone systems, such as type Nl,1 in providing telephone circuits without adding physical conductors. Moreover, many of the existing direct-current facilities would be absorbed to meet signaling needs for the rapid expansion of telephone toll dialing. It therefore became evident that carrier telegraph methods must be adopted for relatively short hauls in fringe areas. The existing 40C1 voice-frequency carrier telegraph system"' 3 was 666