238 BELL SYSTEM TECHNICAL JOURNAL 



The multi-spindle cases used in potting the small size coils for 

 16 and 19-A.w.g. cables ranged in capacity from 12 to 24 phantom 

 units. The larger size coils used on the coarser gage cables were potted 

 in smaller complements. 



Occasionally it is desireible to install side circuit loading alone 

 and to install the phantom loading at a later period. Accordingly, 

 cable loading coil cases were designed to meet these conditions. The 

 open wire coils were potted in individual cases. 



II. Loading for Repeatered Circuits 



General. The development of telephone repeaters to the point 

 where they could be used for commercial service in extending the 

 range of telephone transmission was the beginning of a new era in the 

 communication art. In this development work, the adaptation of the 

 lines to the requirements of repeater operation was secondary in 

 importance only to the development of satisfactory repeater elements 

 and circuits for associating the repeater elements with the line. The 

 reader is referred to an Institute paper by Messrs. B. Gherardi and 

 F. B. Jewett ^ for general information regarding telephone repeaters 

 and to a more recent Institute paper by Mr. A. B. Clark ^^ for a general 

 discussion of subsequent developments in the application of repeaters 

 to long telephone circuits. 



The early work on the line problem was primarily concerned with 

 obtaining a sufficiently high degree of regularity in the line impedance- 

 frequency characteristics, so that the requisite high degree of balance 

 could be obtained and maintained between the line and the repeater 

 balancing network. Later on, particularly in preparing for the ap- 

 plication of telephone repeaters to long toll cables, such as the New 

 York-Pittsburgh-Chicago cable, it became necessary to change the 

 fundamental transmission characteristics of the loading. 



Early Work — Reduction of Line Irregularities. Commercial teleph- 

 ony, requiring two-way transmission, imposes severe balance require- 

 ments on repeater circuits over the entire band of frequencies which 

 the repeater is designed to transmit, in order to avoid singing or dis- 

 tortion due to near singing. Within certain limitations, the higher 

 the degree of balance between the line and the balancing network 

 circuit, the higher will be the permissible amplification gain of the 

 repeater. 



« "Telephone Repeaters," B. Gherardi and F. B. Jewett, Trans. A. I. E. E., Vol. 38, 

 1919, p. 1287. 



'""Telephone Transmission over Long Cable Circuits," A.B.Clark, Trans. 

 A. I. E. E., Vol. 42, 1923, p. 86; Bell System Technical Journal, Jan., 1923. 



