NEUTRALIZATION OF TELEGRAPH CROSSFIRE 



427 



considerable length in a previous paper. ^ Such transpositions con- 

 sist in interchanging systematically the pin positions of the two wires 

 of a pair and of the wires of the two pairs comprising a phantom cir- 

 cuit. It should be clearly understood that while these transpositions 

 are effective in balancing a two-wire or metallic circuit against other 

 circuits, they cannot be used to balance ground-return circuits (such 

 as the telegraph circuits in question) against each other; however, 

 their effect in varying the separation of the different wires from each 

 other has a great influence on the coupling between the ground- 

 return circuits. 



A possible transposition section for an open-wire phantom group 

 is shown in Fig. 7. It will be seen that the two wires of a pair are 



Fig. 7 — Line transpositions of open-wire phantom group 



always adjacent to each other and will therefore have considerable 

 coupling; a wire of one pair is adjacent to a particular wire of the 

 other pair for only one-fourth of the distance, and wires of the two 

 pairs will therefore have much less coupling. 



A brief consideration will make it clear that coupling between 

 wires of separate phantom groups is comparatively small. Each 

 wire of the group 1 to 4 occupies pin position 4 only one-fourth of 

 the distance, and if 5 to 8 be phantomed each wire of the latter group 

 will use pin position 5 one-fourth of the distance. It follows that 

 a wire of group 1 to 4 will be adjacent to a particular wire of group 

 5 to 8 only one-sixteenth of the distance in a long circuit. If 5-6 be 

 non-phantomed however each wire of the pair will use position 5 

 half of the time and will be adjacent to each wire of 1 to 4 one-eighth 

 of the way. The next crossarms above and below are each two feet 

 distant and carry wires transposed so as to minimize the coupling. 



*"The Design of Transpositions for Parallel Power and Telephone Circuits," 

 H. S. Osborne, Proc. A. I. E. E. 1918, Vol. XXXVII p. 739. 



