SPARK GAP SWITCHES FOR RADAR 



595 



rates, one of 600, the other of 1000 pulses per second. They were also to 

 operate for short periods at 2.25 microseconds and 330 pulses per second . The 

 main problems in the design of such a tube were those of obtaining an ade- 

 quate service life and a sufficiently low starting voltage. 



As pointed out in Il-(b), the life of an aluminum cathode gap of this type 

 is critically dependent upon the anode-cathode spacing. For this tube a 



Fig. 21— Western Electric 1B22 sparic gap tube. 



spacing of appro.ximately 150 mils was selected, the gas pressure being 20 

 inches of 75% hydrogen and 25% argon. This gave a life of about 500 

 hours for the 0.75 microsecond pulse, and a much shorter life for the 2.25 

 microsecond pulse. However, since the latter pulse duration is used only 

 a small part of the time, the service life proved to be adequate. In order 

 to obtain the maximum life from each tube, it was necessary that the anode 

 and the cathode depart no more than a few mils from concentricity. Other- 

 wise the sparking would not be uniformly distributed radially, leading to a 



