TRANSMISSION LINES FOR RADIO SYSTEMS 



427 



radiation of energy is a phenomenon essentially associated with the 

 terminals of the line or points of discontinuity which set up reflected 

 waves. 



It may be concluded from Carson's mathematical investigation that 

 the radiation resistance is a term to be added to the impedance of the 

 line at the terminals or points of discontinuity and that it does not 

 appear in the propagation constant. On this basis, the power radiated 

 by a practical balanced transmission line is negligibly small when com- 

 pared to the power being transmitted by the line except perhaps for 

 operation at the very short wave-lengths. 



E.xperimental data for the attenuation in open-wire lines which are 

 as complete as those already shown for concentric-tube lines are not 



1.5 



1.0 



as 



0.6 

 0.5 

 0.4 



0.3 

 02 



0.1 



5 6 8 10 20 



FREQUENCY-MEGACYCLES 



30 40 50 60 80 lOO 



Fig. 11 — Experimental observations of attenuation in a 600-ohm line comprising 

 0.162-inch copper conductors. The points are observed values. The lower curve is 

 calculated only on the basis of copper losses. 



available for this paper. Some typical observations for 600-ohm lines 

 constructed with No. 6 B & S semi-hard drawn copper wire appear 

 in Fig. 11. The points are experimental observations. The lower 

 curve was computed for the case 1830 e.m.u. copper resistivity. The 

 observed values are about 66 per cent higher than the computed values. 



The experimental procedure was as follows. A line 2000 feet long 

 was carefully balanced and terminated by an iron wire line '^ for each 

 of the experimental observations. By means of a portable calibrated 

 indicating device the average currents for the one-half wave-length of 



I'' See Section VII. 



