1316 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1956 



Fig. 23(a) shows representative curves of output power as a function of 

 input power for several values of helix voltage. This information is re 

 plotted in Fig. 23(b) in terms of gain as a function of output power. We 

 see that the TWT operates as a linear amplifier for low output levels. 

 As the output level is increased, the tube goes into compression and* 

 finally a saturation level is reached. The maximum gain at low input 

 levels is obtained with a helix voltage of 2,400 volts (about 10 per cent 

 higher than the synchronous voltage because of space charge effects). 



2 



a 



3 

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50 



45 



40 



35 



30 



5 



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20 



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 lii 

 cc 



Q. 



5 

 o 

 u 



I- 

 z 



LU 

 L> 



a. 



LU 

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15.0 



Z 12,5 



o_i 



S.v, 10.0 



Z' 



Q- U1 

 I LU 



QUJ 



HCC 

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5liJ 



7.5 



5.0 



2.5 



15.0 



zCi 



I LU 

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I e> 

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12.5 



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7.5 



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-5 5 10 15 



POWER INPUT IN DBM 



20 



25 





 28 



^,-1 



30 32 34 36 38 



POWER OUTPUT IN DBM 



Fig. 23 — See opposite page for caption 



