TRANSMISSION LINES FOR RADIO SYSTEMS 



445 



scheme is particularly advantageous where for operating reasons it is 

 useful to connect any station antenna to a particular receiving unit. 

 A board set up for this purpose is shown in Fig. 22. 



Concentric-tube lines may be employed as standards of resistance 

 when other standards become questionable. Since the agreement be- 



800 

 600 



100 

 80 



12 



d 



d+1 



20 22 24 



F"ig. 23 — A scheme for obtaining a calculable radio-frequency resistance standard 

 which is essentially nonreactive and which is adjustable over wide limits of re- 

 sistance. 



tween theoretical and experimental values of radio-frequency resist- 

 ance has been found very good at frequencies at high as 20 megacycles 

 the theory may be considered adequate for much higher frequencies. 

 One scheme for utilizing this situation so as to obtain an adjustable 



