VA RIA BLE EQ UA LIZERS 



243 



useful for systems where it is necessary to introduce variable equali- 

 zation without attenuation of the channels having the lowest signal 

 level. 

 The final structure is shown in Fig. 12. Its chief point of interest 



ru 



2Z2 



iZ| 



xz, 



Z2 



X 



^z, 



uH 



2Z2 



4> 



4Z2 



-[-^] 



M 14 



1.5 2.0 



Wo 



3.5 



Fig. 12 — A variable equalizer adapted to a general controlling impedance. 



is the fact that the controlling element, instead of being a variable 

 resistance, is a variable general impedance, which has been labelled 

 xZ\ in the drawing. In practical cases, of course, Z\ will ordinarily 

 be a simple resistance, inductance, or capacity. In addition to the 

 variable branch the network also includes two fixed branches propor- 



