142 BELL SYSTEM TECHNICAL JOURNAL 



are usually referred to by colors and are so designated on the map. 



As a regular procedure most of these chains operate about six hours 



each day. Following are the numbers of radio stations served by 



each chain together with the lengths of telephone circuit involved. 



(An additional chain which operates only one hour each week is not 



included.) 



Radio Telephone 



Stations Circuit Miles 



Red network 5 41 10,500 16,600 kilometers 



Purple network 41 8,450 13,600 



Blue network 12 3,650 5,900 



Green network 8 3,600 5,800 



Orange network 5 1,700 2,700 



Brown network 3 450 700 



Total 110 28,150 45,300 



' See table on Fig. 1 for revised data as of September 1. 



On occasions when events of particular importance take place, 

 several of the regular chains may be merged together and additional 

 circuits added so as to pick up programs from various parts of the 

 country. For example, on November 5, 1928, the evening before 

 the United States presidential election, the networks shown in Fig. 2 

 were in operation, about 85 radio stations being mcluded. At various 

 times during this evening, five separate programs were broadcast from 

 several different points in New York City; Palo Alto, California; 

 Little Rock, Arkansas; and Pittsburgh, Pennsylvania. The United 

 States was thus virtually one great auditorium, with listeners esti- 

 mated as no less than fifty million. 



From the technical standpoint, program transmission circuits are, 

 of course, very different from message telephone circuits. In the 

 first place, message telephone circuits must be arranged so that to 

 and fro conversations can take place practically instantaneously. 

 Program transmission circuits on the contrary are single-direction 

 transmission circuits. They are, therefore, not complicated by prob- 

 lems of electrical echo, singing and the like, which are ever present 

 with long message telephone circuits. However, although free from 

 the problems of two-way working, the design and operation problems 

 of program transmission circuits are by no means easy as compared 

 with those of message telephone circuits. On the contrary, in many 

 respects, these problems are considerably more difficult, the reason 

 being that the requirement as to approach to absolute fidelity of 

 reproduction is much more severe than for message telephone circuits. 



A frequency band width of 2,500 cycles furnishes, if properly util- 

 ized, a telephone circuit over which speech is transmitted very clearly 

 so that conversations may be easily carried on. This band is not 



