7-7] 



IF AMPLIFIER DESIGN 



367 



R c 



Fig. 7-6 Typical IF Amplifier Configuration Showing How Proper Choice of C 

 Can Self-Neutralize the Stage. (Lead Inductance Has Been Neglected.) R^Xc- 



Stages must provide adequate dynamic range and thus are operated in a 

 manner which allows large peak transconductances to occur. The per- 

 missible gain in these stages should therefore be less than in the early 

 stages when a tube of the same type is emiployed in both places. The gain 

 can be controlled by lowering the impedance of the coupling network or 

 by allowing a greater bandwidth in the stages. The maximum allowable 

 gain is sometimes limited to 



M 



ax gain 



0.2 



i 



:fCo 



(7-25) 



where gm is the peak transconductance and Cgp is the grid-plate capacitance. 

 The effective noise bandwidth 5„ is the parameter involved in radar 

 performance computation. For any practical amplifier this is very nearly 

 the 3-db bandwidth 



Bn 



G(co) 



1 + 



1 r" 



: T / G(co)do) 



; recei 

 an be | 



/co C0o\ "") 



(7-26) 



where G(a)) is the power spectrum of the receiver. The normalized power 

 spectrum of the radar receiver usually can be given by 



(7-27) 



where coo is the midband frequency 

 B is the 3-db bandwidth 

 n is the number of poles in a flat circuit 

 m is the number of groups of circuits. 

 The 3-db bandwidth is 



(21/- - iy''"Bi, 



(7-28) 



