WAVEGUIDE TESTIXG WITH MILUMICROSErOXD PULSES 



39 



Since only one of these pulses can be used to get the desired repetition 

 rate, it is necessary to eliminate the other pulse. This is done in a simi- 

 lar manner to that used for gating out the undesired pulses in the re- 

 generative pulse generator. However, it is not necessary to use another 

 amplifier, as was required there, since the same tube can be used for 

 this purpose, as well as for producing the microwave pulses. Its beam 

 forming electrode is biased negatively about 250 volts with respect to 

 the cathode, and then is pulsed to the normal operating potential for 

 about 50 millimicroseconds during the time of the first short pulse ob- 

 tained by gating the helix. Thus, the beam forming electrode potential 

 has been returned to the cutoff value during the second helix pulse, 

 which is therefore eliminated. 

 Il A block diagram of the resulting double-gated pulse generator is 

 shown in Fig. 3. Comparison with Fig. 1 shows that it is simpler 

 than the regenerative pulse generator, and it has also proved more 

 satisfactory in operation. It can be used at any frequency where a sig- 

 nal source and a traveling-wave amplifier are available, and the pulse 



Fig. 2 — Envelopes of microwave pulses at the output of a traveling wave am- 

 lifier with continuous wave input and helix gating. The gating voltage is higher 

 or the lower traces. 



