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BELL SYSTEM TECHNICAL JOURNAL 



transposition in a at E. Due to the deviation d of segment CE, the 

 near-end crosstalk between a and c in length CF will not be suppressed 

 but will be proportional to d. There will likewise be near-end crosstalk 

 between c and b in the length A C proportional to d. The two devia- 

 tions, therefore, introduce interaction crosstalk practically proportional 

 tod\ 



Fig. 18 — The eifect of deviations in segment length on interaction crosstalk. 



Since there will be small deviations in numerous other segments of 

 circuit &, the deviation d in circuit a will introduce numerous other 

 interaction crosstalk paths similar to that discussed above. The 

 r.m.s. value of the total interaction crosstalk caused by deviations in 

 segment lengths may be roughly estimated as follows: 



2FKyr\j^ 



4 



AFKh^ 



41 



^A6aD 



<aD 



where r is the r.m.s. deviation, L is the line length, D is the nominal 

 segment length and a is the line loss in db per mile, all distances being 

 expressed in miles. The above expression varies about as the 1.75 

 power of frequency and as the square of r. The corresponding 



/I 



expression for transverse crosstalk, i.e., Fi^r -i/y^ varies as the first 



power of frequency and of r. It follows that, if the rules for accuracy 

 of transposition pole spacing are relaxed or the maximum frequency is 

 raised, the effect of pole spacing on interaction crosstalk increases 

 more rapidly than the effect on the transverse crosstalk. 



