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BELL SYSTEM TECHNICAL JOURNAL 



heavy loading systems when used on 10-A.w.g. conductors. This ex- 

 plains the more general use of the medium-heavy loading, which was 

 less expensive because of the greater distances between coils. The 

 effects under discussion are due to the part played by the loading 

 coil resistance. The loading coils themselves conformed as closely 

 as practicable to the cost-equilibrium principle : — a condition of cost 

 balance where a small improvement in transmission would require 

 approximately equal expenditure whether by improving the loading 

 or by adding copper to the cable conductors. On this basis, a some- 

 what less expensive grade of coil was used on the 13-A.w.g. wires 

 than on the 10-A.w.g. wires. The grade of coils developed primarily 

 for use on 16 and 19-A.w.g. cables, giving transmission results illus- 

 trated in Items 5-8 of Table V, was in turn less expensive than the 

 "high efficiency" coils. In each case, since the phantom circuits were 

 somewhat more efficient than their associated side circuits, a some- 

 what higher grade coil was used in the phantom circuits than in the 

 side circuits. 



Open Wire Phantom Loading. Phantom loading came into general 

 use on open wire lines at about the same time as on quadded cables. 

 In general, the methods used in applying phantom group loading to 

 the open wire lines were used for the cable systems. The line char- 

 acteristics for the side circuits were practically the same as for the 

 original non-phantomed circuits (Table III); the principal difference 

 being that caused by the small resistance of the phantom loading 

 coils. The important linear and transmission characteristics of the 

 phantom circuits are given in Table \T. The phantom loading 

 coil had an inductance value of 0.163 henry. 



Loading Coils. Table VH gives general information regarding the 

 first standard side circuit and phantom loading coils used in the 

 phantom group loading systems listed in Tables V and M. The coils 



TABLE VI 



First Standard Open Wire Phanlom Loading 



