OP EN -WIRE CROSSTALK 



207 



determined for each pair combination. Approximate methods of 

 computation have been worked out for doing this and checked against 

 measurements. The computations are involved in connection with 

 far-end crosstalk since the "tertiary effect" is controlling. Since the 



1^ A\ 



V VI 



PN 



^ 



) V 



d| I d2 I 



(A) 



I d3 I d4 I I 



(B) 

 Fig. 23 — Effect of drop brackets on crosstalk. 



summation of crosstalk due to drop brackets is a consistent effect, 

 "drop bracket type unbalances" can be worked out and used in 

 transposition design. This matter is so complicated, however, that 

 the practical method of design is to first practically ignore the drop 

 bracket efTect and then check the design to determine whether this 

 effect has been properly suppressed. 



Certain rules are adopted, however, to ensure that the transposition 

 arrangements are properly chosen to avoid the larger drop bracket 

 effects. Fig. 23-B indicates an arrangement of transpositions for two 



