SPARK GAP SWITCHES FOR RADAR 



575 



indicated that there is no gas clean-up effect associated with gap operation, a 

 fact that was later proved by careful measurement of gas pressure before and 

 after operating gaps of this type. A section through the anode of this gap, 

 Fig. 9 (a), shows that the anode deposit is not compact but assumes the form 

 of a coral-like structure. This low-density deposit must, however, be 

 electrically equivalent to a compact surface as shown by the constancy of 

 the operating characteristics with time. 



In view of the success of this design it was decided to develop gaps^)f the 

 unit type having anodes well enclosed by the cathode surfaces. An attemi)t 

 to make a more practical gap is that shown in the photograph and radio- 



400 500 600 



TIME IN HOURS 



Fig. 8 — Maximum and minimum operating voltages as a function of lime, for three 

 unit gaps of the type shown in Fig. 7, when operated in series. 



graph, Fig. 10, both of which were taken after 750 hours operating time. In 

 this gap the anode is an aluminum rod rounded at the end mounted con- 

 centrically with the enclosing cathode which has a hemispherical closed end. 

 The corona point was added to facilitate starting. Because of the higher 

 anode gradient the sparking was confined to the end region of the tube as 

 indicated in the radiograph, and for this reason we have designated this 

 design an "end sparking tube". A section through the anode, Fig. 9 (b), 

 shows a deposit which in this case is compact due to the fact that the moving 

 spark is confined to a smaller area than in the previous tube, Fig. 7 (a). It 

 is to be noted also that the scattered material is less in extent than that 



