Engineering Requirements for Program Transmission 



Circuits* 



By F. A. COWAN, R. G. McCURDY and I. E. LATTIMER 



Present-day program networks are reviewed from the standpoints of 

 engineering, design, and operation as developed to meet the needs of 

 the broadcasters. The factors requiring consideration in the further 

 development of program networks in anticipation of future needs are 

 also discussed. The presentation of the paper is supplemented by a 

 demonstration of the quality obtainable by transmission over various 

 types of telephone facilities. 



Introduction 



THE growth of radio broadcasting to the magnitude of a major national 

 industry within the last twenty years has been accompanied by the 

 development of a nation-wide system of wire-line networks interconnecting 

 hundreds of broadcasting stations. Papers have been presented before 

 this Institute from time to time^'-'^ describing the types of plant used for 

 these networks and discussing important features of their design and opera- 

 tion. With these twenty years of experience as a background, it should 

 now be of interest to review how the various requirements of broadcasting 

 have influenced the development of the networks and to consider some of 

 the factors which have determined the point to which transmission and 

 operating features have so far been carried. 



Simply stated, broadcasting is a means by which sounds originated at one 

 place are reproduced simultaneously to large numbers of listeners distributed 

 over wdde areas. The simplest possible radio broadcasting system would 

 consist of a microphone, a radio broadcast transmitter and some radio 

 receiving sets. Such a system could serve only the listeners within the 

 comparatively limited service area of the transmitter. To serve the whole 

 nation many transmitters must be established about the country. Further- 

 more the most desirable sources of program are not usually in the neighbor- 

 hood of the transmitter to which a particular listener can tune, since talent 

 tends to be concentrated in certain parts of the country, and special events 

 of interest may occur anywhere. To give a true country-wide service so 

 that every listener can hear the programs he enjoys wherever they may 



* Presented at A.I.E.E. Winter Convention, Philadelphia, Pa., January 27-31, 1941. 

 Published in Electrical Engineering, Transactions section, April 1941. 

 ' For all numbered references, see list at end of paper. 



235 



