VACUUM TUBES AS HIGH-FREQUENCY OSCILLATORS 115 



100 

 80 



60 



50 

 40 



- 10 

 I- 

 ? 8 



100 150 200 300 400 500 600 800 1000 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 18 — A comparison plot of the outputs obtained with the tubes of Figs. 5, 7, 

 and 10. The sloping lines are fixed values of the ratio of output to the square of 

 wave-length. 



different values of the ratio of output to the square of the wave-length. 

 With radiation-cooled tubes patterned after those illustrated, outputs 

 of only a few tenths of a watt at 3000 megacycles can be expected. 

 If larger outputs are to be obtained, innovations in tube design must 

 be made. 



Positive Grid (Barkhausen) Cscillator 



As first reported by Barkhausen and Kurz ^ in 1920, oscillations at 

 frequencies greater than 300 megacycles can be produced by most 

 high-vacuum triodes having symmetrical cylindrical structures when 

 the grid is operated at a fairly high positive potential and the plate is 

 held at or near the cathode potential. When so used they are variously 

 known as oscillators of the Barkhausen and Gill-Morell ^ types after 

 the earliest experimenters, or oscillators of the positive grid or re- 



