Telephone Equipment for Long Cable Circuits 1 



By CHARLES S. DEMAREST 



Synopsis: Some of the important developments contemplated in the 

 apparatus and equipment for long toll cable circuits are described. The 

 large number of equipment units per station in the cable plant and the 

 greater number of stations in a given length of cable than in an open-wire 

 system have made the economic importance of the equipment design such 

 that a comprehensive program of development, affecting many types of 

 equipment, has been undertaken. The outstanding features of some of 

 the more important of these, including the telephone repeater equipment, 

 test board equipment and signaling equipment, are described. The neces- 

 sity for compactness in the dimensions of equipment units, uniformity in 

 assembly arrangements, and simplicity in design, together with the need 

 of careful correlation of the electrical and mechanical requirements, are 

 emphasized. The methods proposed for meeting these requirements 

 generally, are described. 



Introduction 



THE use of lead covered cables in place of bare copper wires for 

 long distance telephone lines has been an important development 

 and much interesting information on this subject has already been 

 presented to the Institute. The engineering and construction features 

 involved in a cable system of this sort were described by Mr. Pilliod 2 

 in his article on the Philadelphia-Pittsburgh Section of the New York- 

 Chicago cable, while the transmission characteristics of such a system 

 were brought out in the recent paper by Mr. Clark. 3 It is the pur- 

 pose of the present paper to deal with some of the important develop- 

 ments in apparatus and equipment which are contemplated for the 

 cable plant. 



A cable system requires repeater stations at more frequent intervals 

 throughout its length than an open-wire line, because of the much 

 smaller gauge conductors which it employs and the increased elec- 

 trical capacity due to closer proximity of the wires. Consequently, 

 in such a system, a greater proportion of the plant investment is 

 represented by the equipment within the offices than is the case with 

 open-wire construction. Furthermore, the number of equipment 

 units per station in a cable system is ordinarily much larger than in 

 an open-wire office, due to the fact that the chief advantages in the 

 use of long cable circuits, in place of open-wire construction, have 

 occurred on routes carrying heavy traffic where many circuits are 



1 Presented before A. I. E. E., June 27, 1923. 



2 Journal of the A. I. E. E. for August, 1922; and Bell System Technical Journal, 

 July, 1922. 



3 Transactions of A. I. E. E., Vol. 38, part 2, p. 1287; and Bell System Technical 

 Journal, January, 1923. 



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