. The Bell System technical journal . Fig. 10—Photograph and radiograph—actual size—of end sparking unit gap, afteroperating 700 hours with a 65-anii)ere pulse of one microsecond duration and repeated1660 times a second. than in the case of the former and supports the use of the unit type gap inwhich this process can be utilized. A cylindrical cathode enclosing a rod 578 BELL SYSTEM TECHNICAL JOURNAL anode also behaves in this way and its erosion rate differs but little from theend sparking type of tube; in fact, the practical gaps to be described inIl-(f) are essentially of this type. With th
. The Bell System technical journal . Fig. 10—Photograph and radiograph—actual size—of end sparking unit gap, afteroperating 700 hours with a 65-anii)ere pulse of one microsecond duration and repeated1660 times a second. than in the case of the former and supports the use of the unit type gap inwhich this process can be utilized. A cylindrical cathode enclosing a rod 578 BELL SYSTEM TECHNICAL JOURNAL anode also behaves in this way and its erosion rate differs but little from theend sparking type of tube; in fact, the practical gaps to be described inIl-(f) are essentially of this type. With these facts in mind it would appear that gaps could be designed tomeet a variety of pulsing conditions if the total number of ampere hours fora pre-assigned life were known, for the electrode areas could be so adjustedthat the changes in gap spacing would be as small as required. Analysis ofthe gradients associated with the end sparking type of gap shows that there X 10 5O D CATHODELOSS CATHODE LOSSFROM SPARKING ARE/ TU. 2 3 4 5 PULSE DURATION IN MICROSECONDS Fig. 11—Cathode loss, in grams per coulomb, as a function of i)ulse duration showingeffect of gap design. can be a considerable build-up on the anode before there is much change inthe maximum gradient which determines the spark-over voltage. Experience with gaps designed for a variety of pulsing conditions showedthat substantial anode build-ups could be tolerated without interfering withoperating conditions, but not as much as theory would predict for an unex-pected factor had a controUing influence on gap life. This factor was thefailure of the spark to keep moving under certain conditions with the resultthat spikes were grown on the anode which introduced a rapid deterioration SPARK GAP SWITCHES FOR RADAR 579 of the operating range due to an increase in anode gradient and also in partto a decrease in gap spacing. Both the relatively large anode build-up, which may be tolerated withoutinterference with gap
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