A NEW MICROWAVE TRIODE 



549 



Noise Figure 



In a forward looking program it is well to keep in mind other possi- 

 bilities for this tube, such as use in a straight through type of repeater in 

 which all of the amplification is obtained at microwave frequencies. In 

 such an application the noise figure of the triode becomes one of its 

 limitations, since the 416A must compete with the low noise figure of 

 the silicon crystal converter which, for the New York-Boston circuit, is 

 around 14 db. Data on thirty five early experimental and production 

 41 6A tubes gave an average value of 18.08 db at 4060 mc* Each of the 



1000 

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 800 

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600 



300 



17 1 



NOISE 



8 19 20 21 



FIGURE IN DECIBELS 



Fig. 24. — Noise figure vs gain-band product for close-spaced triode. 



tubes was operated at 200 volts with 30 ma space current and was tuned 

 so as to present matched impedances to the input and the output wave- 

 guides. The best of this batch had a noise figure of 14.79 db and the 

 poorest 23.2 db. These measurements were made with a fluorescent light 

 noise source.^ 



An interesting correlation between noise figure and gain-band product 

 was uncovered during these tests, as can be seen in Fig. 24, which gives 

 the noise figure in db on the abscissa and the gain-band product in mega- 



* More recently, a sample of twelve production 416A tubes ranged from 13.5 to 16.2 

 db and averaged 15.06 db noise figure, with a standard deviation of 0.8 db. 



