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BELL SYSTEM TECHNICAL JOURNAL 



which depends upon the choice of Z. An additional control of can 

 of course be obtained by the introduction of an auxiliary structure in 

 front of the variable resistance. As in the previous example, the 

 illustrative curves are drawn on the assumption that the characterizing 



sa^Ro 



.*- 



= <'+5^) 



Ro^ 

 2a 



2a2-2a+i 



0.5 



2.5 



3.0 



1.0 1.5 2.0 



UJQ 



Fig. 9 — A variable equalizer requiring only one general impedance branch. 



impedance Z is a simple inductance. It will be observed that the 

 curves "see-saw," the attenuation at certain frequencies increasing 

 while that at other frequencies is decreased. This phenomenon 

 depends upon the choice of the parameter a. It disappears when a is 

 assigned either extreme value ^ or 1, and becomes most pronounced 

 at the intermediate value a = 1/V2. A similar effect can also be 



