OPEN^WIRE CROSSTALK 



53 



Upon the transpositions in a complicated way, because the various 

 interaction crosstalk couplings involve a variety of propagation 

 distances and, therefore, have a variety of phase angles. If both 

 circuits are transposed frequently but alike the direct crosstalk is not 

 affected by the transpositions but it is ordinarily small compared with 

 the indirect transverse crosstalk. 



Figure 16 indicates by a dashed line another type of interaction 

 crosstalk involving the product of two far-end crosstalk couplings. 

 This effect can be neglected with practical arrangement of transpo- 

 sitions but may be important in the case of circuits having few trans- 

 positions or none at all. 



In computing type unbalance the far-end crosstalk in an untrans- 

 posed segment of line of length D may, therefore, be written as: 



FiK 



2t 



2jD 1 



— - FK- 



--2 7© 



27 



approx. 



Since the magnitude of Fi is ordinarily about equal to that of F, the 

 measured coefficient, it is usually satisfactory to use the latter value. 



Fig. 17 — Far-end crosstalk in length 2D between circuits a and b with each circuit 

 transposed at the middle. 



Having derived the above expression it is now possible to derive the 

 far-end type unbalance for two transposed circuits. Figure 17 indi- 

 cates a parallel between two long circuits. The type unbalance will 

 be computed for a length 2D in which both circuits are transposed at 

 the center. In the length 2D three far-end crosstalk paths must be 

 considered, that is, the far-end crosstalk in length AB, that in length 



