OPEN-WIRE CROSSTALK 



37 



circuits a and h, there being an interposed tertiary circuit c. Inter- 

 action crosstalk involving two near-end crosstalk couplings is con- 

 sidered since this is usually the controlling type. There is an inter- 

 action crosstalk path designated r between the first two segments as 

 indicated by Fig. 9A. There is a similar path between the third and 

 fourth segments. Each of these paths would produce a far-end 

 crosstalk current in circuit h at point E. For similar circuits these 

 currents would be equal in magnitude and would add directly. The 

 two currents can be made to cancel by transposing one of the circuits 

 at C, the midpoint of the parallel. Such a transposition also cancels 

 the transverse far-end crosstalk in length A C against that in length CE. 

 There remains, however, the interaction crosstalk between length CE 

 and length A C. 



— ° — 



(A) 



CB) 



Fig. 9 — Effect of transpositions on interaction crosstalk. 



I 



Figure 9B shows a transposition at C in circuit a and also other 

 transpositions whose purpose is to minimize the interaction crosstalk 

 between length CE and length AC. This crosstalk coupling, desig- 

 nated by r', is a compound effect, depending on the near-end crosstalk 

 between circuit a and circuit c in length CE and the near-end crosstalk 

 between c and b in length AC. The near-end crosstalk coupling 

 between a and c in length CE can be greatly reduced by a transposition 

 in circuit a at point D, while the crosstalk coupling between c and b in 

 length A C can likewise be reduced by a transposition at point B in 

 circuit b. The latter two transpositions would not, however, minimize 

 the interaction crosstalk between CE and AC with circuit b as the 



