Engineering Aspects of the TH Microwave Radio Relay System

The TH radio relay system is the most recent in the succession of radio facilities developed for use in the Bell System communication network. A point-to-point radio system was used as part of the commercial telephone network as early as 1920.1 This and subsequent pointto-point radio installations were special cases using a single-hop, narrowhand system to carry one or a few telephone conversations across terrain where installation of wires or cables was impracticable. The use of radio relay as a general purpose facility in the Bell System network was inaugurated with the installation of the experimental TD-X system between New York and Boston in 1947. From this initial 220-mile route, the radio network had expanded by the end of 1900 to over 44,000 route miles carrying over twenty-nine million telephone circuit miles and 79,000 television channel miles. The major portion of this network is provided by the long-haul broadband TD-2 system operating in the 4000-mc common carrier 1459 14(J0