SPARK GAP SWITCHES FOR RADAR 



579 



of the operating range due to an increase in anode gradient and also in part 

 to a decrease in gap spacing. 



Both the relatively large anode build-up, which may be tolerated without 

 interference with gap operation, and the nature of spike growth, which lim- 

 ited useful life, are illustrated in the radiographs, Fig. 12. It is to be noted 

 that the spike is almost of uniform cross section along its length and radio- 

 graphs made at various stages of its formation show that growth takes place 



Fig. 12 — Radiographs showing two views of the uniform deposit and subsequent spike 

 growth on the anode of an end sparking unit gap. 



at its end. This indicates a high concentration of negative ions in the vapor 

 prior to deposit on the anode. 



Life test data in which the i)ulse repetition rale was kept constant at 200 per 

 second are shown in Fig. 13 for gaps having a fixed spacing but in which the 

 peak current is varied (a), and for gaps having a variety of spacings but in 

 which the peak current is kept constant (b). The life is measured in terms 

 of hours to the beginning of spike growth. Both "end sparking" and "side 

 sparking" tubes were employed in the tests. These data clearly show that 



