TRAVELING WAVE TUBE FOR O-OOO-MC RADIO RELAY 1325 



4.5 



5.0 5.5 6.0 6.5 7.0 7.5 



FREQUENCY IN KILOM EGACYCLES PER SECOND 



8.0 



Fig. 30 — Low-level gain and helix voltage for maximum gain as functions of 

 frequenc}' for several beam currents. The TWT was matched to the waveguide 

 (with tuners where necessary outside of the 5,925 to 6,425-mc range) at each fre- 

 (luency. The solid curves show the gain-frequency characteristic with the helix 

 voltage adjusted for maximum gain at 6,000 mc for each beam current and then 

 held constant as frequency was changed. Experimental points correspond to this 

 condition. The dotted curves show how the characteristics change when helix 

 voltage is optimized at each frequency. The optimum helix voltage increases by 

 about 100 volts in going from 6,000 down to 4,500 mc because of slight dispersion in 

 the phase velocity of the helix. 



4.3 Operation Over an Extended Range 



We now turn to a consideration of tj^pical Ml 789 characteristics over 

 an extended range of beam current, frequency, and magnetic field.* We 

 shall concentrate on two items, the low-level gain and the maximum 

 power output. From variations in these quantities the complete compres- 

 sion ctirves can be roughly deduced. This situation is illustrated in Fig. 27 

 which sho^vs output as a function of input at different beam currents. 

 While the shapes of these curves are slightly different, for the most part 

 they can be derived from the 40-ma curve by shifting it along the abcissa 



* The characteristics of the tuV)e used for the low-level gain measurements 

 in this Section were slightly different from those of the tube used for the maxi- 

 mum output measurements and both were slightly different from those of the 

 tube used for the measurements of Section 4.2. All tubes, however, had charac- 

 teristics falling within the ranges listed above. 



