The TD-2 Microwave Radio Relay System

U P E R - H I G H or microwave frequencies began to attract the interest of communication research engineers during the late '30s. The practical application of microwaves to commercial communication circuits was delayed by the outbreak of World War II, but the microwave techniques which had already been developed were employed to advantage in the prosecution of the war. The concentrated development effort and mass production of microwave equipment for military applications greatly expanded the engineering knowledge and production skill in this relatively new communications field. After termination of the war, it was possible again to devote the necessary development effort toward application of microwave techniques to commercial purposes. In the Bell System this effort was applied to the development and construction of a long-haul radio relay system. A broad-band multi-channel radio relay system now connecting some of the main communication centers of the United States, as shown in Fig. 1, represents the combined efforts of a Bell System team since 1945.1 This chain of stations carrying hundreds of message circuits or a television picture on each broad-band channel, in giant 25 to 30-mile strides across the country, has opened up a new radio field. The first step was the development of an experimental system placed in service in November 1947 between New York and Boston. 2 Upon the successful completion of this project objectives were established for a system, which is called the TD-2 Radio System, capable of extension to at least 4000 miles with upwards of 125 repeaters.