756 



BELL SYSTEM TECHNICAL JOURNAL 



Equations (13) and (14) are based on the assumption that the phantom 

 circuit is sufficiently well transposed to secure balanced voltages, cur- 

 rents, and charges on the four wires. The capacitance of the phantom 

 circuit is, of course, affected by the capacitances of its component wires 

 to the other wires of the lead and to ground and also by the capaci- 

 tances of the insulators. 



The losses which contribute to the leakage conductance of phantom 

 circuits are similar to those which have been discussed for side circuits. 

 The ratio of the phantom circuit leakage conductance to that of the side 

 circuit will depend upon the relative magnitudes of these different 

 losses. Varying relations between the different types of losses give a 

 ratio of phantom circuit leakage conductance to side circuit leakage 

 conductance which might conceivably range between the extremes of 

 1 and 6. For practical engineering purposes, however, the leakage con- 

 ductance of the phantom circuit is generally assumed to be twice that 

 of the side circuit. 



500 



250 



If) 



I 

 O 



-250 



0— — 



20 30 40 



FREQUENCY — KILOCYCLES 



10 



Fig. 19 — Impedance of phantom open-wire circuits. 



50 



Curves of the attenuation of non-pole pair 12-inch phantom circuits of 

 different gages are depicted in Fig. 18. In most cases the attenuation 

 of the phantom circuit is somewhat less than that of the corresponding 

 side circuit. Frequently, however, the advantage of lower attenuation 

 is under practical conditions more than offset by the large noise and 

 crosstalk effects experienced on the phantom circuits. 



Values of the dry weather impedance of 12-inch phantom circuits are 

 presented in Fig. 19. It will be observed that the impedance of a 

 phantom circuit averages about 60 per cent of the impedance of a 12- 

 inch side circuit. 



