TRAVELING WAVE TUBE FOR 6,000-MC RADIO RELAY 1315 



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0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 



COLLECTOR VOLTAGE IN KILOVOLTS 



1.8 



2.0 



2.2 



Fig. 22 — Intercepted current as a function of collector voltage with helix and 

 accelerator voltages held constant at their nominal values. Below the knee of the 

 curves about three quarters of the total intercepted current goes to the heli.x and 

 about one quarter is focused all the way back to the accelerator. Curves are shown 

 for no rf input and for output levels of 1, 5, and 10 watts. With no input, the lowest 

 permissible collector voltage is determined by the phenomenon of space charge 

 blocking. With rf input, it is determined mainly b3' the velocity spread of the 

 electrons. In all cases it was found that the alignment of the TWT with respect 

 to the magnetic circuit becomes more critical as the knee of the curve is ap- 

 proached. For this reason the M1789 is usually operated with a collector voltage 

 about 200 volts above the knee. 



modulation, will be divorced from the discussion as outlined above and 

 treated separately in Sections 4.4 and 4.5. 



4.2 Operation Under Nominal Conditions 



Basic Characteristics 



By nominal conditions for the Ml 789 we mean the following: 



frequency 6175 mc (band center) 



beam current 40 ma 



magnetic flux density 600 gauss 



collector voltage 1200 volts 



