A new multichannel teletype terminal for use on long-range high-frequency radio systems

THIS paper will describe, on a systems basis, a new multichannel teletype terminal which has been designed for the main-line intercontinental radio circuits of the Army Command and Administrative Network (ACAN). This network provides the backbone of the traffic-handling facilities between the United States and major overseas commands largely utilizing single-side-band transmission and reception. The continuity of communications required in this service makes reliability of paramount importance. Therefore, the equipment must be capable of operating effectively under adverse conditions of long-range radio propagation. The heavy traffic load necessary in maintaining the extensive overseas forces imposes the additional major requirement of maximum communication channels per radio circuit. To meet the varied requirements for teletypewriter, voice and facsimile channels, and the rigors of service in poorly controlled environments sometimes necessary in military operations, a basically new multichannel terminal was required for this service. A glance at the older type of terminal equipment shown in Fig. 1, and which currently is in standard use, will quickly show the inadequacies which led to this new design. At the start of World War II, this adaptation of the Western Electric Company type-40C1 voice-frequency carrier telegraph equipment was in use by the Army to provide up to six channels of teletype over a single radio circuit. This system is still in use and employs 2-tone frequency diversity for each channel mark and space. From Fig. 1, at least one major conclusion is apparent: the ten bays of equipment are quite a space outlay for six 60-words-per-minute (wpm) teletype channels. Also, the equipment is by no means adaptable in regard to temperature and humidity. It is essentially commercial-type, fixed plant gear, and must be treated as such if it is to perform properly.