I.O.iniKG FOR riUJiPIfONE CIRCUITS 231 



After placin.u llu' siMiulles of coils in the xarious compartments, 

 the case is tilled with a moisture proofmt; compound. The lead- 

 sheathed cable stub is brought through a brass nipple in the cast 

 iron cover of the case, and the cover is then bolted to the case. By 

 means of a special design of case and cover jfiint, a double seal is 

 provided to prevent entrance of moisture at this point. A wiped 

 joint is made l)etween the lead sheath of the cable and the brass nipple. 



The conductors in the stub cable have an appropriate color scheme 

 in their insulation to identify the terminals of the loading coils, thus 

 facilitating splicing of the coils into the line circuits. A series of 

 multi-spindle cases was standardized, ranging in capacity from 21 

 to 98 coils. Smaller quantities of coils w^ere potted in a single spindle 

 pipe type case. 



Generally similar assembly and potting methods were used for the 

 open wire coils, the important differences being first, that the open 

 wire coils were always mounted in individual cases designed for mount- 

 ing on pole fixtures, and secondly, that the coil terminals were brought 

 out of the case in individual rubber-insulated leads. 



I. Phantom Group Loading 



In Mr. Gherardi's paper reference was made to the development of 

 means for (a) phantoming loaded circuits and (b) loading phantom 

 circuits. The large plant economies made possible by these develop- 

 ments have resulted in extensive applications of these principles. 



The following discussion will consider first the coil winding schemes, 

 after which the transmission characteristics of the loading systems 

 and the electrical characteristics of the loading coils will be briefly 

 described. 



Loading Methods. Fig. 4 schematically illustrates the Bell System 

 standard method for loading phantom circuits and side circuits of 

 phantoms.'' 



The loading problem is to introduce the desired inductance into 

 each of the three circuits of a phantom group without causing objec- 

 tionable unbalances. The method illustrated in Fig. 4 involves 

 individual loading coils for each circuit, the design being such that 

 the side circuit coils are substantially non-inductive to the phantom 

 circuit, while the phantom loading coil is substantially non-inductive 

 to the side circuits. These desirable results require close magnetic 

 coupling between the line windings in each coil. Consequently, in 



■ U.S. Patents No. 980,021 "Loaded Phantom Circuit," G.A.Campbell and T. Shaw. 

 No. 981,015 "Phantomed Loaded Circuit," T. Shaw. 



