74 BELL SYSTEM TECHNICAL JOURNAL 



annual costs of the various plans over proper periods as well as first 

 costs. 



Loading 



Loading coils are now connected to many of the circuits and all of 

 the circuits in this cable are intended to be equipped with coils located 

 at 6000-foot intervals. The theory and practice of loading are de- 

 scribed in papers previously presented before the Institute^ and for 

 our purpose it will be sufficient to state that these loading coils very 

 materially reduce the attenuation losses and improve the quality of 

 transmission as compared to cable circuits not so equipped. The im- 

 provement in so far as the attenuation losses are concerned, varies 

 with the type of circuit and loading coils, but with one of the No. 19 



Fig. 15 — Loading Coils Connected to a Group of Four Wires and Arranged for 



Phantom Operation 



A. W. G. circuits in this cable loaded with coils having an inductance of 

 0.175 henry located at 6000-ft. intervals, the losses are only about one- 

 third as great as in a similar circuit without the coils. The connections 

 and arrangements of the coils are shown in Fig. 15 and it will be noted 

 that coils have been connected to both the physical and phantom cir- 

 cuits. The arrangement is such that there is no appreciable inter- 

 ference between circuits due to magnetic action in the iron cores of the 

 different coils or to the necessarily close electrical relation in the 

 windings. 



The loading coils are potted and sealed in iron pots, two of which 

 are shown in Fig. 16, and in the country these are mounted on pole 

 fixtures. Each pot contains 36 groups of 3 coils each. The pots are 

 nearly 30 inches in diameter at the flange, 52 inches high and weigh 

 about 2700 pounds. The pots can be obtained in different sizes 

 depending upon the number of coils which it is desired to install at 

 one time. When the cable was installed, extra lead sleeves were 



1 Papers by M. I. Pupin, Transactions of A. I. E. E., XVII, May 1900 and 

 XV, March 1899. 



Paper by Bancroft Gherardi, Transactions of A. I. E. E., XXX, June 1911. 



