TRAVELING WAVE TUBE FOR 6,000-MC RADIO RELAY 1321 



For these measurements power output was held constant by adjusting 

 input level at each voltage. The figure shows that as helix voltage is 

 increased, the compression decreases but the AM-to-PM conversion 

 increases. The choice of a helix voltage at which to operate the tube 

 must therefore represent a compromise between these quantities. 



Phase Modulation Sensitivity 



The equipment of Fig. 24 was also used to measure the phase modula- 

 tion sensitivity of various electrodes by omitting the amplitude modula- 



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SWEPT VIDEO 



SIGNAL SOURCE 



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VIDEO FREQUENCY IN MEGACYCLES PER SECOND 



10 



Fig. 26 — Example of frequency response shaping caused bj' AM-to-PM con- 

 version. This figure shows the calcuhited frequency response viewed between 

 FM terminals for the system shown in the block diagram. Curves are given for the 

 case in which the phase modulation generated in the TWT both adds to and sub- 

 tracts from that of the transmitted signal. Inclusion of a limiter at point A would 

 result in a flat frequency response. 



