Radio Frequency Interference Considerations in the TD-2 Radio Relay System

The number of microwave systems that may he used on a particular frequency assignment in a given area is determined by the mutual interference between the systems. The Bell System is particularly conscious of this problem because of its extensive use of broadband microwave systems. At the end of 1958 the Bell System had in operation approximately 215,000 one-way broadband channel miles of microwave systems in the United States, corresponding to approximately 7,000 transmitters and an equal number of receivers. A large portion of this extensive network makes use of the TD-2 radio relay system 1,2 operating in the 3700- to 4200-mc band. The TH system 3 operating in the 6-kmc range is under active development, and the T.J system operating in the 11-kmc common carrier band (10,700 to 11,700 mc) is now in commercial use. Equipments made by other manufacturers also operate in the 4- and 6-kmc bands. In spite of the highly directive antennas now in use, a certain fraction of the transmitter power from any station will be radiated in directions other than that for which it is intended, and this becomes a potential source of intrasystem interference to itself and also to other systems operating in the same frequency band. 369