VACUUM TUBES AS HIGH-FREQUENCY OSCILLATORS 129 



value. To fix the time of flight and hence the frequency of oscillation, 

 the magnetic field and plate voltage must be adjusted to certain values 

 roughly expressed by the empirical relationship 



X7/= 13,100, 



(4) 



where X is the wave-length in centimeters and H is the field strength 

 in gausses, which must also satisfy equation (3). It is found that for 

 best operation the magnetic and electric fields within the tube should 

 not be exactly perpendicular. This lack of perpendicularity may be 

 achieved either by tipping the magnetic field relative to the tube axis 

 or by introducing end plates within the tube and maintaining them 

 at a fixed positive potential. 



Kilgore ^^ has given complete information concerning this type of 

 oscillator. In Fig. 29, taken from his paper, is shown the dependence 



1000 



500 550 600 650 700 750 800 



FREQUENCY IN MEGACYCLES PER SECOND 



F"ig. 29 — Relation of magnetic field and anode potential to frequency of oscillation 

 in magnetron oscillator of second type. 



of field strength and anode potential on the desired frequency. The 

 existence of a preferred frequency fixed by these values is confirmed 

 by the data in Fig. 30 relating the output and wave-length with the 

 length of the attached Lecher system. The decreased output shown 

 at the second peak is due to the added losses introduced by the ex- 

 tended length of the system. The outputs shown on these curves 

 are not in watts, but represent relativ^e readings of the field strength 

 near the oscillator. With optimum adjustments 7 watts at 715 

 megacycles is reported, the efficiency being about 8 per cent. The 

 dependence of output and frequency on the applied anode potential 



