ADMITTANCES OF TARALLEL PLAN E ELECTRON TUBFJi 625 



where SWR is the voltage staiidiiif^ wave ratio mentioned above. The deter- 

 mination of a series loss resistance in this manner is quite analoj^ous to 

 the short-circuit test used in determininjf the losses in a power transformer. 

 There is one other factor in the cot cot technique which is worthy of 

 mention. If, at the very beginning, the output line is terminated in Zo/ 

 and if the transformer is adjusted so that the input line is matched, then 

 tlie value of ;;/ will be unity and p will equal zero. It is then unnecessary to 

 take a cot-cot curve. It is, however, still necessary to locate Vo by shorting 

 the terminals at .to . 



Diode Admittance at 4060 Megacycles 



Electron stream admittance measurements with diodes were made in the 

 following way: A coaxial tester was installed and the circuit was adjusted 

 for a slope m of about one. This coaxial tester was then removed and re- 

 placed by another in order to learn whether the slope obtained with one 

 tester would be the same with another, supposedly identical, tester. This 

 process was repeated several times, and the slope was found to vary no more 

 than about 10% from one tester to the other. 



The procedure was then to replace the coaxial tester with a diode and make 

 admittance measurements with the assumption that the slope would be 

 the same for the diode as for the tester. This assumption was believed to be 

 reasonable since the structure of the diode was identical with that of the 

 tester except that an anode was substituted for the coaxial output connector. 

 In either case all elements that were located inside the w^aveguide cavity 

 were presumably identical. 



Electron stream measurements were made at a frequency of 4060 mega- 

 cycles with a number of diodes over a wdde range of anode and heater 

 voltages. In making these measurements, the radio-frequency power was 

 kept at a relatively low level (0.2 milliwatt) in order that the measured 

 admittances would be independent of the radio frequency voltage. 



Results for several diodes are shown in Figs. 6 through 13. The various 

 symbols used in the figures are defined as follows: 



Vh = heater voltage 



Ih = heater current 



I'o = anode voltage (neglecting contact potentials) 



/o = anode current in ma 



Jo = anode current density in ma/cm- 



gQ = low-frequency diode conductance measured with an audio fre- 

 quency bridge 



g = high-frecjuency diode conductance measured as described above 



b = high-frequency diode susceptance 



Rs = equivalent resistance in series with diode 



In computing the admittance of the electron stream it was necessary to 



