REFLEX OSCILLATORS 



599 



than the guide. This is desirable in a radar receiver for circuit reasons, 

 which require that the cathode of the oscillator be at ground potential. 



The iris size is a compromise chosen to provide sufficient sink margin 

 throughout the band. An iris coupling inherently varies with frequency 

 and provides a weaker coupling at lower frequencies. Hence, since a suffi- 





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Fig. 91. — A performance diagram for the 2K50 at the high frequency band limit. This 

 diagram shows loci of constant power as a function of the admittances presented at the 

 plane of the tube window. Admittances are normalized in terms of the characteristic 

 admittance of the wave guide. 



cient sink margin must be provided at the wavelength where the coupling 

 is a maximum, this means that an e.xcess of sink margin exists at the low 

 frequency end of the band. This is illustrated by the impedance perform- 

 ance diagrams of Figs. 91 to 93. 



The 2K50 presented a difficult mechanical problem which will be appreci- 

 ated when the minute dimensions of the resonant cavity are observed in 



