3A FM Terminal Transmitter and Receiver

As indicated in a companion paper, FM terminals perform the initial and final modulation steps in the T D - 3 microwave radio system. 1 The FM transmitter converts the baseband signal to a frequency modulated signal centered at 70 M H z ; the FM receiver performs the reverse function of recovering the baseband modulation from the FM signal. Although primarily intended for use in the T D - 3 system, the 3A FM terminal equipment* also is used for improved performance in the TD-2 system. 2 Design emphasis was placed on: (i) reliability and minimum maintenance through the use of solid-state circuitry throughout, (ii) im* M a n u f a c t u r e d by the Western Electric C o m p a n y for Bell System use only. 1423 1424 T H E BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1!)G8 proved performance consistent with the more stringent T D - 3 objectives, and (in) reduced cost and size. The types of baseband signals to be transmitted over the terminals are discussed by S. D. Hathaway and others. 1 In general terms they consist of 1200 message circuits comprising two multiplex mastergroups or a single NTSC* color television signal. FM terminals are required at each end of a radio route and at intermediate points where the baseband signal or some portion of it must be added or dropped. The 3A design is based on a maximum of 16 terminal pairs in tandem in 4000 miles.