8-15] 



LINEAR ANALYSIS OF AGC LOOPS 



419 



stability and dynamic response of the AGC loop is often difficult to achieve 

 in combination with other requirements on d-c regulation (proportional to 

 AGC loop gain) and fidelity of intelligence modulation. For pulsed radars 

 where fast AGC action is desired (common in monopulse systems), methods 

 for analyzmg sampled-data servos must be used and the AGC loop band- 

 width is limited to about half the repetition rate by stability considerations. 



8-15 LINEAR ANALYSIS OF AGC LOOPS 



Design of AGC loops is based upon a first order or linear approximation 

 to the nonlinear action of the IF amplifier for small deviations from average 

 operating points.^ This approximation is illustrated in Fig. 8-1 6a. The 



Output 



Delay 



(a) 



. ^ 



AGC 

 Filter 



Ki=lncremental IF Gain 



Constant 



K2=lncremental AGC Loop Gain 



, e, = Constant 



(b) 



Fig. 8-16 Linear Approximation to AGC Loop. 



upper block diagram in this figure shows the essential components of an 

 AGC loop. The nonlinear relation of the IF amplifier gain to the AGC bias 

 is indicated by Gi(eg). The system equations have the following forms: 



eo = e,KsG,{e„) (8-4) 



e,= {ea- eo)G,{s). (8-5) 



^B. M. Oliver, "Automatic Volume Control as a Feedback Problem," Proc. IRE, 36, 

 466-473 (1948). 



