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BELL SYSTEM TECHNICAL JOURNAL 



circuit and a second noise source related to active grid loading effects. ^^ 

 The optimum IF amplifier input circuit design involves primarily the 

 selection of impedance transformation means which results in the maximum 

 over-all signal-to-noise performance for the radar receiver. It can be shown 

 that this optimum value of impedance transformation is not that value which 



600 600 1000 



2000 

 IN OHMS 



10,000 



Fig. 26. — Simplified equivalent input circuit of an intermediate frequency amplifier 

 and noise-figure vs signal source impedance. 



maximizes the signal but rather is a condition where a definite signal mis- 

 match obtains. This may be understood by an inspection of the character- 

 istics of the two fictitious noise sources illustrated. The shot noise con- 

 tribution of the vacuum tube employed in the input IF amplifier stage is 

 here represented by the series noise generator Vt . Under conditions of 

 shorted grid this is the only effective noise contribution, and this procedure 

 offers a simple method for determination of the magnitude of this ctTcct. 



''"Considerations in the Design of a Radar IF Ami)lifier," Andrew L. HopiJcr and 

 Stewart E. Miller, Proc. /. R. £., November 1947. 



