THE RADAR RECEIVER 



741 



to meet the over-all gain requirement. The over-all gain of a multistage 

 amplifier employing synchronous single- tuned interstage networks is 

 given by 



\ IttCtB ) 



where Ct represents the total interstage shunt capacitance and B is the over- 

 all band width requirement. Table II presents the individual interstage 

 band widths and the maximum over-all gain obtainable for multistage IF 

 amplifiers having a 5 mc over-all band width requirement. Here the use of 

 the 6AK5 pentode is assumed and the total interstage shunt capacitance is 

 assumed to be 12 micromicrofarads. It should be observed that unavoidable 

 misalignment of circuits, aging of tubes, and other such effects all tend to 

 reduce the idealized computed performance under the practical military 

 radar conditions and must be considered thoroughly in the design. 



Table II. — Interstage Band Width and Over-all Gain of Multistage IF Amplifiers 



The double-tuned interstage network configuration shown in Fig. 27 is 

 a somewhat more efficient circuit form than the single-tuned variety just 

 discussed, and because of this improved performance has been employed to 

 about the same extent as the synchronous single-tuned type during the past 

 war. Its performance advantage lies in the basic fact that the transmission 

 response curve for this structure has a flat-top characteristic resulting in a 

 slower rate of over-all band width reduction as these circuits are cascaded. 

 The ability to separate the output plate and the input grid circuit capacitances 

 and the elimination of the plate-to-grid coupling capacitor with its additional 

 parasitic capacitance to ground results in a greater gain-per-stage perform- 

 ance. In this structure the resonant frequency of both primary and second- 

 ary circuits corresponds to the midband IF and the conditions of equal Q 

 of primary and secondary circuits and critical coupling are assumed. These 

 conditions result in a smooth flat-topped response characteristic having 

 optimum gain performance. The relationship between the individual inter- 



