Long Distance Cable Circuit for Program Transmission* 



By A. B. CLARK AND C. W. GREEN 



The rapid growth of the telephone cable network in this country has 

 made it desirable to develop a system whereby this network may be utilized 

 to transmit programs for broadcasting stations over distances upwards of 

 2,000 miles. Such a system has recently been developed and given a trial on 

 a looped-back circuit 2,200 miles long with very satisfactory results. It 

 transmits ranges of frequency and volume somewhat in excess of those now 

 handled by the open-wire circuits which are used for program work, and 

 also in excess of those handled by present-day radio broadcasting systems 

 when no long distance lines are involved. 



The paper deals first with the transmission requirements of broadcasting 

 systems and then gives a description of this new cable system. 



AS discussed in two recent papers, ■• one of which was presented 

 before this Institute, telephone circuits are now extensively used 

 for chain broadcasting. Radio broadcasting stations covering various 

 local areas in the United States are connected together by wire circuits 

 so that programs are delivered simultaneously to all of them. Thus, 

 it is possible to deliver a program to the whole nation at once. About 

 35,000 miles of telephone circuits are now being regularly utilized for 

 this service and about 150 radio broadcasting stations receive pro- 

 grams from one or more of the chains of wire circuits. 



Today practically all of this service is being furnished by means of 

 open wires using voice-frequency channels. Long distance cable 

 routes are growing rapidly and are supplementing the open-wire 

 routes, particularly those carrying very heavy traffic. Fig. 1 shows 

 the long distance cable routes now in use in the United States, together 

 with the additional routes proposed for installation within the next 

 few years. The advantages in placing some circuits in these cables 

 which will adequately handle program transmission service were evi- 

 dent and led to the development described in this paper. 



Because of the special characteristics which program transmission 

 circuits must possess it was necessary to develop an entirely new type 

 of cable circuit, in which the method of placing the wires in the cables, 

 the type of loading and all of the apparatus, including amplifiers and 

 distortion correcting apparatus for both amplitude and delay, differ 

 radically from other cable circuits. The development was recently 

 completed and a trial installation made in which wires were looped 



^ F. A. Cowan, "Telephone Circuits for Program Transmission," presented 

 at Regional Meeting of S.W. District of A. I. E. E., Dallas, Texas, May 7-9 

 1929. Proceedings of A. I. E. E., July, 1929, A. B. Clark, "Wire Line Sys 

 terns for National Broadcasting," presented before the World Engineering Con 

 gress at Tokio, Japan, October, 1929, Proceedings of I. R. E., November, 1929 

 Bell System Technical Journal, January, 1930. 



* Presented at Convention of A. I. E. E., Toronto, June, 1930. 



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