378 



THE RADAR RECEIVER 



Gain Control Bus 



r^ 



1^2 



X^2 



1^2 



Plate 

 C ' X Voltage 

 Supply 



L2 Heater 



Supply 



Fig. 7-10 Typical Arrangement of IF Stages Showing Arrangement of Decoupling 

 Circuits and the Feedback Paths Thereby Introduced. 



To obtain maximum receiver sensitivity the charge must be removed. This 

 removal occurs with a nonlinear time constant 



C, 



+ <?^(/) 



Short time constants must be used to avoid gain modulation of desired 

 signals when there are large undesired signals such as clutter appearing in 

 the receiver. Grid current may also produce a similar situation, and the 

 time constants must be kept short while at the same time providing 

 sufficient decoupling at low frequencies and at bandpass frequencies. 



The plate circuit decoupling is perhaps more critical than the other 

 circuits. With a ladder decoupling chain, the d-c path must be kept low in 

 resistance so that the plate voltage is not dropped excessively. Inductors 

 are therefore used as the series elements. The elements nearest the power 

 input connection have the currents of several tubes flowing through them. 

 When several stages are driven into saturation, each of the stages will send 

 a transient input into the decoupling chain. This transient propagates 

 along the chain and may result in a very complicated transient at the last 

 stage which can gain modulate that stage, causing undesirable transient 

 gain variations following strong pulse signal inputs. To avoid this phenom- 

 enon, adequate filtering is provided between the ladder tapping point and 

 the tube. 



