The TJ Radio Relay System

821 822 822 823 824 825 828 828 845 850 850 853 859 861 862 862 865 867 870 871 871 874 877 877 During the past decade, microwave radio in the Bell System has had a phenomenal growth. In terms of route mileage and number of circuits, this growth has been primarily in the long-haul field in the 4,000-mc common carrier band. The TD-2 system 1 2 now criss-crosses the continent several times and provides facilities for telephone and 821 822 TIIE BELL SYSTEM TECHNICAL JOURNAL, JULY . 1 9 6 0 television to almost every part of the continental United States.* In many areas it is already loaded to capacity and, hence, its use for other than backbone service is becoming increasingly restricted. In the next decade it is expected that there will be a large demand for shorthaul microwave facilities along backbone routes and remote rural areas. These will have to be supplied by systems operating in common carrier bands other than the 4,000-mc band. To allow for orderly growth of the Bell System radio plant, the 11,000-mc band has been selected for short-haul service needs where the maximum channel cross section might be only a few hundred telephone circuits. In the past, the telephone companies have used 4,000-mc TE equipment, 3 secondary TD-2 arrangements or other currently available 6,000mc common carrier equipment to fulfill their short-haul needs. Feasibility studies 4 by the radio research group at Bell Telephone Laboratories and systems engineering studies made in cooperation with the telephone companies indicated the possibility of and need for a new economical short-haul system that would permit the dropping and adding of circuits at each repeater or alternatively, be capable of transmitting monochrome or NTSC color television.