242 



BELL SYSTEM TECHNICAL JOURNAL 



The sixth network, shown in Fig. 1 1 , is structurally more elaborate than 

 any which have preceded it. Its design equations are also relatively 



6-^ = 1 + ^ 



m 



2 Z 



pQo 



= [' 



RoJ 



Zii Zpi — Re 



rRo 



Wo 



3.5 



Fig. 11— A variable equalizer with zero loss at one frequency for all settings 

 of the controlling element. 



elaborate and difificult to deal with. It possesses, however, the salient 

 property that when Zu = 0, perfect transmission of power from one 

 terminating impedance to the other is secured at any setting of the 

 variable resistance. This property suggests that the network may be 



