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THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1951 



of opposite core-quadrants. The line windings were inserted in the four 

 line wires of the phantom circuit and connected to have all of the mutual 

 inductances aid the self inductances. In the individual side circuits the 

 mutual inductances opposed the self inductances, and in consequence the 

 coils contributed negligible leakage inductances to the circuits. The phantom 

 coils were about twice as large in weight and volume as the associated side 

 circuit coils, for cost-equilibrium reasons. 



The side circuit coils were closely similar in size to the existing standard 

 non-phantom coils. Each of their two line windings consisted of an inner- 

 section winding on one half-core and an outer-section winding on the other 



SIDE CIRCUIT COILS 



PHANTOM CIRCUIT 

 COIL 



INNER WINDINGS 

 OUTER WINDINGS 



Fig. 2 — Phantom group loading. Coil winding schematics and method of connection 

 into circuit. 



half-core, and thus in effect were evenly distributed about the entire core. 

 The close magnetic-coupling thus obtained resulted in a negligible leakage 

 inductance to the phantom circuit in the parallel-opposing connections of 

 line windings. The mutual inductances aided the self-inductances in the 

 side circuits. 



Figure 2 schematically illustrates the coil winding arrangements. The 

 general design symmetry of the individual coils also included essential 

 symmetry in the distribution of the direct admittances among the line 

 windings and from the line windings to the core and the case. The initial 

 designs so well satisfied the service needs that only a very few minor design 

 refinements were subsequently required from the crosstalk standpoint. 

 The real difficulties encountered in meeting the service crosstalk-require- 



