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THE BELL SYSTEM TECHXICAL JOIRXAL, JANUARY 1957 



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4 6 8 10 20 40 60 80 tOO 200 400 600 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 7 — Input potentiometer term. 



potentiometer loss, and seriously limiting feedback. In this design an 

 acceptable compromise is made when the ratio of network capacitance 

 to grid-cathode capacitance has been fixed at 1.2 as suggested b}" Bode.^ 

 The gain through the input network and the deviation from one-third 

 cable shape is shown in Fig. 6. A typical potentiometer term is shown 

 in Fig. 7 



Similar considerations apply to the output network with the further 

 restriction that the impedance presented to the output tube should be 

 about 40,000 ohms at the top edge of the band for optimum modulation 

 performance. 



The coupling networks have a temperature characteristic which must 

 be taken into account in the insertion gain of the repeater. The charac- 

 teristic is due to variations in the resistance of Ci and R2 with tempera- 

 ture. This amounts to 0.005 db per degree F at 20 kc, decreasing with 

 frequency, becoming negligible above 80 kc. 



Beta Circuit 



The beta or feedback network is designed to complement the combined 

 characteristics of the input and output coupling networks and mop-up 

 residual effects, such as those due to mjS effect and coupling network 

 temperature coefficients. The network also provides the dc path for the 

 output tube plate current. 



