OPEN-WIRE TELEPHONE LINES 



735 



especially when used for carrier frequencies, proximity effect is very 

 important, but it is negligible in open-wire circuits because of the large 

 separation between wires. 



The method of determining the skin effect resistance of round wires 

 is presented in various publications, and the theoretical results have 

 been experimentally confirmed on numerous occasions.^ Values of the 



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FREQUENCY- KILOCYCLES 



Fig. 5 — A.-C. resistance of open- wire pairs at 20 deg. cent. (68 deg. fahr.). 



a.-c. resistance of 165, 128, and 104-mil copper pairs at 20 deg. cent., 

 (68 deg. fahr.) determined in accordance with skin effect theory, are 

 plotted in Fig. 5. It will be noted that the increase in resistance due to 

 skin effect is small in the voice range, but rather astoundingly large in 

 the carrier range, amounting at the higher frequencies to from 200 to 

 nearly 400 per cent. 



Experimental evaluations of open-wire resistance are in extremely 



'See "Wave Propagation Over Parallel Wires — The Proximity Effect," J. R. 

 Carson, Phil. Mag., Vol. 41, April 1921, pp. 607-633; "Experimental Researches on 

 Skin Effect in Conductors," A. E. Kennelly, F. A. Liws, and P. H. Pierce, ^. I. E. E. 

 Trans., Vol. 34, Part 2, 1915, pp. 1953-2021, and "Skin Effect Resistance Measure- 

 ments of Conductors at Radio Frequencies," A. E. Kennelly and H. A. Affel, /. R. E. 

 Proc, Vol. 4, No. 6, Dec. 1916, pp. 523-574. 



