422 



BELL SYSTEM TECHNICAL JOURNAL 



a 77-ohm concentric-tube line is 6.38 times as great as that for a 770- 

 ohm open-wire line in which the wire diameter is equal to that of the 

 inner conductor of the concentric-tube line. Thus, the attenuation 

 constant for a practical open-wire line may be approximately the same 

 as that for the larger practical sizes of concentric-tube lines. Some 

 typical computations appear in Fig. 7. A balanced two-wire line of 

 600-ohm characteristic impedance was chosen for the computations. 



In Fig. 7 it was assumed that the proximity effect, that is, the re- 

 distribution of currents owing to the presence of the second conductor, 

 is a correction of negligible magnitude. Only in the case of large con- 



S 20 



1.0 2 4 6 



FREQUENCY-MEGACYCLES 



8 10 



40 



Fig. 6 — Calculated radio-frequency resistance for several common sizes of solid 

 copper conductors. V^alues are for one conductor only. 



ductors closely spaced does the proximity effect perceptibly increase 

 the resistance. This may be seen from Fig. 8 which shows the increase 

 in resistance due to the proximity of the conductors. There are 

 several excellent published articles upon this subject. ^■^■^"•^^ 



The foregoing results give, of course, only the power dissipated in 

 copper losses and tell nothing about radiation losses. If the line 

 spacing is less than 1/10 of a wave-length and if the line length is more 



8 J. R. Carson, Phil. Mag., Ser. 6, Vol. 41, p. 607, April, 1921. 



9 H. B. Dwight, Jour. A. I.E. E., p. 203, March, 1922. 



" H. B. Dwight, Jour. A. I. E. E., p. 827, September, 1923. 



11 S. Pero Meade, Bell Sys. Tech. Jour., Vol. 4, No. 2, April, 1925. The equations 

 given in this reference were employed in computing Fig. 8. 



