Topband: vert lighning protection

[DAVID CUTHBERT]

Phil,

It becomes a contest between the fast and repeatable arc in vacuum and the slow and not so repeatable arc across the spark gap. Only one spark gap will fire of the three. The gap should be set as narrow as possible and still allow you to use the antenna. Figure 70 kV/inch. You might set them to 1/4". The air gap is unreliable because it relies on an electron or ion in the gap for things to get started (the "lucky electron" theory). No electron and the gap will take a microsecond or more to break down. In the mean time the vacuum variable has arced. This will take its toll on the vacuum variable over time as it degrades the vacuum. I suppose the relatively slow risetime of lightning works to your advantage.
  
A HV vacuum relay can be placed across the vacuum cap to protect it. Power it OPEN when you're on the air. When you shut down the station remove the power to the relay and now the vacuum cap is shorted. Newark stocks these. 
  
         Dave WX7G