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BELL SYSTEM TECHNICAL JOURNAL 



The over-all efficiency of operation is the ratio of the peak output to peak 

 input powers or the ratio of average output to average input powers. 



The frequency of oscillation of the magnetron is determined by feeding a 

 small amount of the RF power into a calibrated variable frequency resonant 

 cavity of high Q and by means of a detector observing the frequency at 

 which the cavity absorbs or passes power. 



The load impedance into which the magnetron operates is determined by 

 measurement in the output line of the voltage standing wave and its phase 

 with respect to some previously chosen reference point. This measurement 

 is made with a standing wave detector in which it is arranged to move an 

 electrostatic probe along a section of slotted Hne in which it samples the RF 

 energy in the line. The energy picked up by the probe is detected after 

 sufficient attenuation either by a crystal or by a small bolometer whose 

 resistance is a function of the energy fed into it. The voltage standing wave 



ATTENUATOR 



OSCILLOSCOPE 



HIGH 

 FREQUENCY 

 OSCILLATOR 



Fig. 40. — A schematic diagram showing the arrangement of apparatus used in making 

 measurements on a non-oscillating magnetron or magnetron resonator block. 



ratio and its phase may be translated into impedance, admittance, or reflec- 

 tion coefhcient in the manner already discussed. The magnetron load 

 impedance may be varied from the match presented by the terminating 

 water column by means of a line tuning section or tuner. In one such line 

 tuning section, two sleeves constituting in effect quarter wavelength lines 

 of low characteristic impedance may be moved relative to one another to 

 vary the magnitude, and moved together to vary the phase of the standing 

 wave. 



The Rieke diagram, is a plot of constant output power and frequency 

 on a reflection coefficient plane. Its construction thus involves the measure- 

 ment of output power, frequency, and load impedance as the line tuners 

 are moved over a wide range of positions. The operating parameter main- 

 tained constant is usually chosen to be the peak DC current. Such a dia- 

 gram is shown in Fig. ii. 



