TH-3 Medium-Haul Application: System Considerations

This paper discusses a radio system which has been made available to the Associated Bell System Companies to help meet their demands for high-performance transmission capability. It is made up of the T H - 3 IF heterodyne radio bay and 4A FM terminals along with a number of supporting features. This system was formulated to be a flexible package that may be customized to specific transmission needs within the Bell System. Flexibility results from the optional use of a frequency-diplexed auxiliary channel, a one-by-one baseband protection switching system, a single transmitting/receiving antenna, and the use of shelters to house the equipment. These features collectively distinguish the medium-haul concept from that which is typically called long or short haul. In spite of the difficulty establishing a model for the medium-haul system, since the anticipated applications are so varied, a 1000-mile, 1800-circuit system model (38 hops with 4 baseband switching sections) has been selected. This choice represents a reasonable compromise between the 4000-mile long-haul model and the 250-mile short-haul model and will be used to describe noise and reliability performance. This system will meet the two-way reliability objective 2271