REFLEX OSCILLATORS 563 



the 2K25 did not fundamentally change the design but were rather in the 

 direction of extending its performance to meet the expanding requirements 

 of the radar art. The incorporation of the resonant cavity within the 

 vacuum envelope resulted in a major revision of the sccpe of the designer's 

 problems. He assumed a part of the burden of the circuit engineer in that 

 it became necessary for him to design an appropriate cavity and predeter- 

 mine the correct coupling of the oscillator to the load. The latter trans- 

 ferred to the laboratory a problem which in the case of separate cavity oscil- 

 lators had been left as a field adjustment. 



D. A Reflex Oscillator Designed to Eliminate Hysteresis — The 2K29 



As service experience with the external cavity type of reflex oscillator 

 was gained a number of limitations of such a design became apparent. 

 The ditficulties arose primarily from the conditions of military application. 

 A typical difficulty was the corrosion of cavities and copper flanges under 

 the severe tropical conditions met in some service applications. The diffi- 

 culty of maintaining a moistureproof seal in a cavity tuned by variation 

 of the inductance made it very difficult to alleviate this condition. The 

 success of the all metal technique in the three centimeter range suggested 

 the application of the same principles to the design of a 10 centimeter 

 oscillator and this was undertaken. 



Mechanically, the problem was straightforward, but an extrapolation of 

 the electrical design of the 723A/B to 10 centimeters suffered frcm a fatal 

 defect. The difficulty, previously described in Section VHI, was the dis- 

 continuous and multiple valued character of the output as a function of the 

 repeller voltage. Reference to Fig. 19 will indicate the operational prob- 

 lems which would arise in an oscillator in which the hysteresis existed in 

 marked degree. The a.f.c. systems were such that in starting the repeller 

 voltage would start from a value more negative than required for cscilla- 

 tion and decrease. As the repeller voltage decreased through the range 

 where oscillation would occur the frequency would of course cover a range 

 of values. When the repeller voltage reached a value such that the fre- 

 quency of the oscillator had a value differing from the transmitter by the 

 intermediate frequency the steady shift of the repeller voltage would be 

 stopped and would then hunt over a limited range about the value required 

 to maintain the difference frequency. When adjusted for operation this 

 condition would pertain with the repeller voltage at a value such that the 

 oscillator would be delivering maximum power. If under operating con- 

 ditions the frequency required of the oscillator by the system drifted to that 

 corresponding to the amplitude jump at B, any further drift of frequency 

 could not be corrected. Thus, one effect of the hysteresis is to limit the 

 electronic tuning range. As a second possibility, let us assume that the 



