OPE N- WIRE CROSS TA LK 



21 



positions and used in working from short lengths to long lengths is 

 discussed at length. The next section of the paper is devoted to the 

 efifect of constructional irregularities caused by pole spacing, wire sag, 

 "drop bracket" transpositions, etc. Various "non-inductive" wire 

 arrangements are considered. The paper closes with a general 

 discussion of practical transposition design methods based on the 

 principles previously disclosed. 



Underlying Principles 



The discussion under this heading will cover the general causes of 

 crosstalk coupling between open-wire circuits and the general types 

 into which it is convenient to divide the crosstalk effect. The usual 

 measures of crosstalk coupling will also be discussed. 



Causes and Types of Crosstalk 



The crosstalk coupling between open-wire pairs is due almost entirely 

 to the external electric and magnetic fields of the disturbing circuit. 

 If these fields were in some way annulled there would remain the 

 possibility of resistance coupling between the pairs because of leakage 

 from one circuit to the other by way of the crossarms and insulators, 

 tree branches, etc. This leakage effect is minor in a well-maintained 

 line. It enters as a factor in the design of open-wire transpositions 

 only in so far as the attenuation of the circuits is affected which 

 indirectly affects the crosstalk. 



Figure 1 indicates cross-sections of two pairs of wires designated as 

 1-2 and 3-4. If pair 1-2 existed alone and if the two wires were 

 similar, a voltage impressed at one end of the circuit would result in 



Fig. 1 — Magnetic field produced by equal and opposite currents in wires 1 and 2. 



