716 



BEI.L SYSTEM TKCHXICAL JOlh'.XAL 



to effect an impedance mismatch and thus reduce the interaction between 

 this circuit and the input circuit. The output coupling network, in this 

 case operating at 60 mc, consists, of an inductive impedance tuned with a 

 variable condenser. The outj)ut of this converter is fed into the following 

 IF amplifier by means of a 75-ohm coaxial transmission line. The loss of 

 this converter unit, defined as the ratio of the power of the wanted 60-mc 

 output signal to the signal power impressed ui)on the input terminal, is 



t 368A 

 (800 MC) 



IN 21 r 

 (3000 Mcn 



GL446 

 I (1000 MC) 



IN23 

 (10.000 MC)J 



IN21A 

 (3000 MC)J 



IN25 r 

 (1000 MOi 



IN23A 

 (10.000 MC) I 



IN28 

 (3000 MC) 



IN21B 

 (3000 MC)1 



IN26 

 ^24.000) 



IN23B 

 10,000^ 

 A MC y 



RECEIVER NOISE FIGURE CALCU- 

 LATED FOR POOREST ACCEPTABLE 

 CRYSTAL UNIT UNDER EACH SPECI- 

 FICATION. THE FOLLOWING I-F 

 AMPLIFIER IS ASSUMED TO HAVE 

 A NOISE FIGURE OF 5 DECIBELS. 



Fig. 11. — Chronological development of point-contact silicon crystal rectifiers and 

 associated receiver noise jjerforniance. 



approximately 6 db. 'Ilie noise ligurcof a tyi)ical unit of this tyi)e isa])pr().\i- 

 mately 20 db, this value being of secondary importance since sufticient gain 

 is provided in the associated radio-frequency amplifier. 



At the higher radar frequencies the noise performance characteristics of 

 silicon crystal-point contact rectifiers are considerably better than that of 

 vacuum tubes available during the ])ast war years. Figure 11 outlines the 

 chronological developments of these units with respect to the receiver noise 



