Wire Line Systems for National Broadcasting ^ 



By A. B. CLARK 



The interconnecting of radio broadcasting stations by special telephone 

 lines for the simultaneous broadcasting of radio programs began on a 

 commercial basis in 1923. Today well over 30,000 miles of program 

 transmission circuits are in use in the United States and transcontinental 

 broadcasts by means of such wire lines are a daily occurrence. 



The paper first states the radio limitations which make wire lines neces- 

 sary for broadcast coverage of large nations. A map and data are given 

 showing the present broadcasting chains in the United States and indi- 

 cating the extent of their use. An explanation is given of why program 

 transmission circuits must have transmission characteristics materially 

 different from message telephone circuits and a brief discussion of some 

 of the important transmission characteristics of such circuits, including 

 particularly " frequency range " and " volume range." The present chains 

 in the United States which are made up almost entirely of open-wire cir- 

 cuits on a voice-frequency basis are briefly described. The manner in 

 which these chains are tested and the way control is exercised are also 

 indicated. To exercise this control requires an elaborate network of tele- 

 graph wires now aggregating over 40,000 miles and a corps of special men 

 over 300 in number. 



WHAT we are here considering, as an important factor in pro- 

 moting national solidarity, is the tying together of a whole 

 nation so that a single broadcast will instantly reach even the most 

 remote points. Radio broadcasting stations (employing the more 

 generally used frequencies) are essentially local distribution centers 

 serving effectively points up to 50 miles (80 kilometers) or, in favor- 

 able cases, 100 miles (160 kilometers) or more from the radio trans- 

 mitter. For the larger nations it is evidently necessary to make 

 division into areas, locating a radio transmitter in each area for its 

 coverage, and then to provide a network of circuits connecting the 

 transmitters in the various areas with the point at which the broad- 

 cast originates. At the present time wire telephone systems are 

 employed almost exclusively for this national distribution of broad- 

 casts. It is the purpose of this paper to discuss the wire networks 

 which are now being provided in the United States by the Bell Tele- 

 phone System. 



In the United States at the present time (January 15, 1929) pro- 

 grams are being regularly distributed over extensive wire networks 

 or " chains " as indicated on the map of Fig. 1.- The various chains 



^ Presented before the World Engineering Congress at Tokio, Japan, October, 

 1929, Proc. of the I. R. E., November, 1929. 



- This map has been revised to show the network chains as of September 1, 1929. 



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