OP EN- WIRE CROSSTALK 



201 



For the range of frequencies and accuracy of pole spacing used in 

 practice, it has been found that the effect of pole spacing irregularity 

 on interaction crosstalk is not controlling. This is indicated by Fig. 19 



Z 3000 



5 10 15 20 25 30 35 40 45 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 19 — Far-end crosstalk caused by pole spacing irregularities. 



which shows some measurements of output-to-output far-end crosstalk 

 between long circuits having transposition arrangements designed to 

 make the crosstalk due to type unbalance small compared to that due 

 to irregularities. The curves are about linear with frequency as would 

 be predicted if the effect of the pole spacing irregularities (and wire 

 spacing irregularities) on the interaction crosstalk is neglected. For 

 these particular curves, a knowledge of the pole spacing indicated that 

 pole spacing rather than wire spacing irregularities were controlling in 

 causing crosstalk. 



The above discussion assumes that a transposition section is divided 

 by the transposition poles into segments all of the same nominal 

 length. It is sometimes economical to use segments of different 

 nominal lengths in the same transposition section. If the variation 

 among the segment lengths is consistent rather than accidental it may 

 be allowed for in the design of the transpositions. 



In practice, segments of different lengths are used in the same 

 transposition section when it is desired to adapt for multi-channel 

 carrier frequency operation a few pairs on a line already having many 

 pairs transposed for voice-frequency operation. Such lines often have 

 existing transposition poles nominally spaced ten spans apart while 

 for the pairs retransposed for carrier operation it is necessary to space 

 the transposition poles about two spans apart. In such cases the cost 



