420 



BELL SYSTEM TECHNICAL JOURNAL 



varies as a function of b/a. Note that a moderate departure from the 

 optimum ratio does not greatly increase the Une losses. 



So far it has been tacitly assumed that the conductors were exactly 

 concentric. Eccentricity affects all of the line constants.^ However, 

 experience has shown that the departures from concentricity usually 

 encountered in practice produce no appreciable increase in the attenu- 

 ation constant of the line. 



At commercial installations the actual power loss in the terminated 

 line is measured directly in decibels and has invariably been found to 



4.5 

 1- 4.0 



UJ 

 UJ 



li. 



o 

 g 



(T 3.0 



UJ 



a. 



122.5 



u 



m 



a 



1.5 



1.0 



.4 .6 .8 LO 2 



INNER RADIUS OF SHEATH-INCHES 



Fig. 5— Calculated losses at 20 megacycles expressed in decibels for concentric- 

 tube lines constructed from copper and employing the optimum ratio (3.6) of outer 

 to inner conductor. 



agree with the predictions within the precision of such measurements 

 which is about 0.5 db, in field work. Certain of the lines referred to in 

 this paper have been similarly tested in the laboratory under more 

 favorable conditions and yielded agreements within 0.3 db where the 

 total loss was of the order of 4 to 6 db. 



Briefly summarizing it may be said that the attenuation in well 

 constructed concentric lines is proportional to the square root of 

 frequency, inversely proportional to the diameters (optimum ratio) and 



^ A. Russell, "Alternating Currents," Vol. 1, p. 166, Cambridge Press. 



