The TD-2 Microwave Radio Relay System 



By A. A. ROETKEN, K. D. SMITH and R. W. FRIIS 



(Manuscript Received July 5, 1951) 



The TD-2 microwave radio relay system is a recent addition to the tele- 

 phone plant facilities for long distance communication. It is designed to supple- 

 ment the coaxial system and to provide greatly expanded facilities for nationwide 

 transmission of broad-band signals such as television pictures or large groups 

 of message circuits. The system makes use of many microwave repeaters located 

 25 to 30 miles apart in line-of-sight steps. The great variety and number of 

 components which make up such a system require the engineering of all com- 

 ponents to close tolerances. This paper describes the system in some detail from 

 the standpoints of overall objectives, component designs to meet such objectives 

 and facilities for the maintenance of overall performance. 



I. Introduction 



SUPER-HIGH 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 mihtary applications greatly expanded the engi- 

 neering knowledge and production skill in this relatively new communica- 

 tions 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.^ 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.^ Upon the successful completion of this project objectives 

 were estabhshed for a system, which is called the TD-2 Radio System, 

 capable of extension to at least 4000 miles with upwards of 12vS repeaters. 



The TD-2 Radio System provides no new types of service but will sup- 

 plement existing facihties such as the coaxial system. Therefore, TD-2 

 must provide comparable reliability, economy and quality of service. It is 



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