OPEN-WIRE CROSSTALK 



211 



The mechanical problem of supporting the wires of the "non- 

 inductive" arrangements is considerable if serious increases in crossarm 

 and hardware costs are not to be incurred. This objection seems at 

 present to override the possible advantages of (1) fewer transpositions 

 for a given pole head area and crosstalk result, or (2) fewer trans- 

 positions and lower crosstalk with a greater pole head area. 



Another possibility is the use of non-parallel wires. It is possible to 

 arrange two pairs of wires in such a way that they have a certain direct 

 crosstalk per mile at one end of a span and the value at the other end of 

 the span is about equal and opposite. The net direct crosstalk per mile 

 integrated over the span is zero or small. An example of this is the 

 barreled square formerly used abroad. Fig. 26 illustrates this arrange- 



Fig. 26 — Two pairs of wires in different barreled squares. 



ment. The wires are arranged in groups of four, each four being 

 arranged on the corners of a square. The two wires of a pair are on 

 diagonally opposite corners of a square. Each pair is given a quarter 

 turn in each span. For simplicity only two pairs in different four-wire 



