55t)~ BELL SYSTEM TECHNICAL JOURNAL 



cycles along the logarithmic ordinate. The points scatter between the 

 extremes of 15 db noise tigure for a gain-band product of 2000 megacycles 

 to 23 db noise figure at 400 megacycles gain-band product. Extrapolating 

 from these data, a noise figure of 10 db might be achieved if the gain- 

 band product could be increased to 5500 mc. It is reasonable to expect 

 that an improvement of this amount can be achieved if the resistance and 

 return electron losses inside the tubes can be eliminated.'^ 



We may use these data to determine the expected noise figure of a 

 straight through amplifier, thus: 



h = Fa -\- — J. — + ^ ^ • • • (1) 



Li A (j-.i Uu 



If, for example, we assume that all stages are alike in noise figure and 

 in gain, equation (1) approaches the expression, as the number of stages 

 increases without limit: 



F/rA - 1 



1 im 



F = '^^^^-^ (2) 



n-»oo Cr^i i 



Using an average value of 10 db gain per stage, the overall noise figure 

 would be as follows: 



(1) For Fa = 30 (best tube, 14.79 db) 



F = 299 _ 33 2 or 15.2 db 



(2) For Fa = 64 (average tube, 18.08 db) 



F = ^^ = 7loY 18.5 db. 



Straight-Through Amplifier 



The actual performance of a ten-stage amplifier was about what should 

 be expected from the considerations above. The best tube (10 log F = 

 14.79 db) was used in the first stage, and the next best tube in the sec- 

 ond stage. The measured overall noise figure was 15.96 db. The overall 

 gain was 90 db and the band was flat to 0.1 db for 44 mc. Such an 

 amplifier with its associated power supply and individual control panels 

 is shown in Fig. 25. 



Conclusions 



A circuit is described which lends itself readily to utilizing the 416A 

 close-spaced triode as a modulator or a cascade amplifier for microwave 

 repeaters operating at 4000 mc. Data are {presented on early e.xperimcntal 

 models of the tube. 



As modulators, single tubes hatl from 5 to 9 db gain wilh 10 to 20 



