202 BELL SYSTEM TECHNICAL JOURNAL 



of the carrier channels is appreciably increased if uniform spacing 

 between the new transposition poles is used. The transpositions in 

 the pairs retransposed for carrier operation must be coordinated with 

 the transpositions in the other circuits and it is necessary, therefore, 

 either to divide the ten spans into four approximately equal parts 

 with consequent expense in setting new poles at the quarter points or 

 to retranspose all the circuits on the line. 



To avoid either of these expensive procedures, the new transposition 

 poles are nominally located in the manner indicated by Fig. 20. This 



POLES 

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Fig. 20 — Location of extra transpositions in a ten-span segment of line. 



figure shows ten-pole spans subdivided into four parts in order to 

 create three additional transposition poles. The figure indicates the 

 location of the new transposition poles and the possible methods of 

 transposing at these new poles. For some of the circuit combinations 

 the crosstalk within the ten-span interval is considerably greater than 

 if the four segments were equal in length. In each other ten-span 

 interval the crosstalk is likewise increased by a similar inequality in 

 segment length. Since all ten-span intervals are nominally alike, 

 considerable crosstalk reduction may be obtained by properly designed 

 transpositions located at the junctions of these intervals. 



The use of segments of different lengths inherently decreases the 

 effectiveness of the transpositions in reducing crosstalk and adds to 



