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BELL SYSTEM TECHNICAL JOURNAL 



l)late design is directly j)roportional to the charge density along the plate. 

 Up to now, this density has been assumed to be uniform. When the 

 charge is located on discrete filaments, the restriction of uniform density 

 is no longer necessary and it is possible to modify the delay characteristic 

 as desired by changing the spacing of the filaments in inverse proportion 

 to the desired change in delay. 



The assumption of a flat plate is also useful in simplifying the analysis; 

 in the actual design the equivalent plate is bowed out over the major por- 

 tion of the frequency range to reduce the delay ripple. The final zeros and 

 poles obtained are shown in Fig. 8, in which the carrier-frequency zeros 

 and poles are plotted on an equivalent audio-frequency basis. A total of 29 



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- p 



CO - PLANE 



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+ p 



Fig. 8 — Plot of the zeros and poles of the delay equalizer for 8-k.c program terminals. 



delay sections are required, of which three are assigned to the carrier-fre- 

 quency equalizer and 26 to the audio-frequency equalizer. 



Audio-Frequency Equ.alizer 



To complete the design of the audio-frequency equalizer some means 

 must be found for absorbing the effects of dissipation in the coils and con- 

 densers so that the final dissipative network will exhibit the theoretical 

 non-dissipative performance plus a loss which is constant with frequency. 

 It can be shown that a non-dissipative all-pass section plus a flat-loss pad 

 can be replaced with a dissipative all-pass section (of modified constants) 

 in tandem with a minimum-phase loss equalizer as in Fig. 9. It would be 

 uneconomical to associate a loss equalizer with every phase section; and it 

 is in fact unnecessary, since any minimum-phase device accomplishing the 

 same result will exhibit the same performance.' The problem is then re- 

 duced to equalizing the loss of the network composed of dissipative dela}- 

 sections. 



