MAGNETRON AS GENERATOR OF CENTIMETER WAVES 2G?> 



The pulling figure, PF, defined as the maximum frequency excursion of the 

 magnetron as the load reflection coefficient traverses the p = 0.2 circle, may 

 be obtained from the Rieke diagram. It may be measured directly by two 

 simple wavemeter measurements taken at the frequency extrema occuring 

 as the standing wave of 1.5 voltage ratio is moved up and down the line. 

 Various types of standing wave introducers have been devised to produce a 

 reflection coefficient of p = 0.2 for the specific measurement of pulling figure. 



The performance chart is a plot of constant magnetic field, peak output 

 power and over-all efficiency contours on a V-I plane. Its construction 

 thus involves the measurement of peak DC voltage, peak DC current, and 

 peak output power at several magnetic fields. Sometimes frequency, push- 

 ing figure, and spectrum appearance are also determined. Figs. 17 and 20 

 are examples of this chart. 



The frequency spectrum is the distribution of energy with frequency for a 

 pulsed magnetron and is displayed on a so-called spectrum analyzer. This 

 analyzer is a very narrow band tunable radio receiver whose pass band is 

 varied periodically twenty or so times per second over several mc/s. The 

 response of the receiver to the frequency distribution of energy appears on 

 an oscilloscope whose sweep is synchronized with the pass band frequency 

 variation. 



The pushing figure is the instantaneous frequency change in mc/s per 

 ampere change in peak DC current at constant load. It may be obtained 

 by measuring the frequency shift on a spectrum analyzer as the pulse 

 current is changed by a known amount. The current change must be 

 executed rapidly enough to avoid frequency shifts arising from temperature 

 changes. 



Impedance measurements on the non- oscillating magnetron involve the 

 use of a variable frequency RF oscillator feeding power through an attenua- 

 tor and a standing wave detector into the output circuit of the magnetron 

 (see Fig. 40). These measurements determine as a function of frequency 

 the impedance Zc discussed in the text. 



M ode frequencies are determined from the impedance measurements on the 

 non-oscillating magnetron by noting the frequencies at which the input 

 standing wave is observed to go through a minimum. They may also be 

 determined by the observation of energy maxima with a pickup loop or 

 probe placed in the resonator system. 



Mode identifiication is made by observing the periodicity of RF field in the 

 interaction space of the resonator system. This is done by sampling the 

 field with a rotating RF probe placed in an axial cylinder corresponding to 

 the cathode as shown in Fig. 40. The probe response is detected and dis- 

 played on an oscilloscope with sweep synchronized to the rotation of the 

 probe. 



