462 BELL SYSTEM TECHNICAL JOURNAL 



v Total velocity (A]:)pen(li.\ VIII only). 



V Instantaneous gap voltage 



'ii' Real part of frequency (12.1). 



X Coordinate along heani. 



y :\ rectangular coordinate normal to .v. 



_v Half separation of planes forming s\mmelrical gap. 



3'c Magnitude of small signal electronic admittance. 



z A rectangular coordinate normal to x (Appendix II). 



c A variable of integration (Appendix VI). 



a Negative coeflicient of the imaginary part of frequency (12.1). 



/3 Modulation coeflicient. 



/3o Average value of modulation coefScient. 



/3o Modulation coeflicient on axis. 



/3r Modulation coefficient at radius r from axis. 



0s Root mean squated value of modulation coefficient. 



/3y Modulation coeflicient at distance y from axis. 



7 7 = oi/iio. 



e Dielectric constant of space (8.85 x 10~" farads/cm). 



6 Drift angle in radians. 



6g Gap transit angle in radians. 



X Wavelength in centimeters. 



<!> A phase angle. 



i Reduced potential (g-13). 



a Voltage standing wave ratio. 



T Transit time. 



T Time constant of thermal tuner. 



TH Cycling time on heating. 



Tc Cycling time on cooling. 



\}/ Magnetic flux linkage. 



w Radian frecjuency. 



THE reflex oscillator is a form of long-transit-time tube which has 

 distinct advantages as a low power source at high frequencies. It 

 may be light in weight, need have no magnetic focusing lield, and can be 

 made to operate at comparatively low voltages. A single closed resonator 

 is used, so that tuning is very simple. Because the whole resonator is at 

 the same dc voltage, high frequency by-pass difhculties are obviated. 



The frequency of oscillation can be changed by several tens of megacycles 

 by varying the repeller voltage ("electronic tuning")- This is very ad- 

 vantageous when the reflex oscillator is used as a beating oscillator. The 

 electronic tuning can be used as a vernier frequency adjustment to the 

 manual tuning adjustment or can be used to give an all-electrical autcmatic 

 frequency-control. Electronic tuning also makes reflex oscillators serve 

 well as frequency mcdulated sources in low power transmitters. 



The single resonator tuning property makes it possible to construct (iscil- 

 lators whose mechanical tuning is wholly electronically controlled. Such 

 control is achieved by making the mechanical motion which tunes the cavity 

 subject to the thermal e.xjiansion of an element heated by electron bom- 

 bardment. 



The efficiency of the reflex oscillator is generally low. The wide use of 

 the 707li, the 723A, the 726A and subsequent Western Electric tubes 

 shows that this defect is outweighed by the advantages already mentioned. 



