VARIABLE EQUALIZERS 



239 



The choice of an appropriate Zn therefore requires only routine 

 design methods.'^ The same correspondence with the conventional 

 formula will be found to hold also for most of the design equations to 

 be given later. 



a'^-\ 



Z21 



Z11Z21 -Ro 



Q 12 



ooo 

 Fig. 8 — Variable equalizers with varying reference characteristics. 



A third simple network is shown on Fig. 9. Its properties are the 

 converse of those secured from the structures of Fig. 8. The reference 

 loss, ^0, is now a constant, while ip varies with frequency in a manner 



3 See, for example, "Distortion Correction in Electrical Circuits," O. J. Zobel, 

 Bell Sys. Tech. Jour., July, 1928. 



