OPEN^WIRE CROSSTALK 25 



which is due to charges on tertiary circuits which arise within any 

 thin transverse sUce due to coupHng with the disturbing circuit in 

 that same sHce. This coupHng, in any sHce, causes currents as well 

 as charges in the tertiary circuit in that slice, but, as discussed in 

 detail in Appendix A, the effect of these currents in producing crosstalk 

 currents in the disturbed circuit is small compared with the effect of 

 the charges. The currents and charges in the tertiary circuits in any 

 thin slice due to the coupling with the disturbing circuit in that same 

 slice may be but a small part of the total currents and charges in the 

 slice. The total values are due to couplings of the tertiary circuits 

 with the disturbing circuit in all the slices. When the total values 

 are considered currents as well as charges in the tertiary circuit may 

 be important in causing crosstalk currents in the disturbed circuit. 

 To consider the total currents and charges in the tertiary circuits it is 

 necessary to take account of both the interaction crosstalk coupling 

 and the transverse crosstalk coupling between disturbing and disturbed 

 circuits. 



The nature of interaction crosstalk coupling is indicated by Figs. 2C 

 and 2D which indicate two successive thin transverse slices of width 

 ^ in a parallel between two circuits a and b and the typical tertiary 

 circuit c. Assuming transmission from left to right on circuit a in 

 Fig. 2C this circuit is coupled with c in the right-hand slice by the 

 near-end crosstalk coupling indicated by fiac- This coupHng causes 

 transmission of crosstalk current (and charge) into the left-hand part 

 of circuit c which has both near-end and far-end crosstalk coupling 

 to circuit b. Consideration of these two successive transverse slices, 

 therefore, introduces the two compound couplings tiacncb and Uacfcb- 

 There are two more of these compound couplings as indicated by 

 Fig. 2D. There is a far-end crosstalk coupling between circuits a and 

 c in the left-hand slice which combines with both near-end and far-end 

 couplings in the right-hand slice. The compound types of crosstalk 

 of Fig. 2C and 2D are called interaction crosstalk since the various 

 slices interact on each other in producing indirect couplings. The 

 interaction crosstalk coupling between a terminal of a disturbing circuit 

 and a terminal of a disturbed circuit is defined as the coupling between 

 these points due to the indirect couplings involving all possible combi- 

 nations of different thin transverse slices. 



The distinction between indirect transverse crosstalk and interaction 

 crosstalk is that the former takes account of the effect of indirect 

 crosstalk from disturbing to tertiary to disturbed circuit in a single 

 thin transverse slice while the latter involves indirect crosstalk from 

 primary circuit to tertiary circuit in one slice, transmission along the 



