Engineering Requirements for Program Transmission Circuits

HE growth of radio broadcasting to the magnitude of a m a j o r 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 1 ' 2 - 3 describing the types of plant used for these networks and discussing important features of their design and operation. 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 wide areas. T h e 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. Furthermore the most desirable sources of program are not usually in the neighborhood 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 m a y occur anywhere.