Topband: vertical lightning protection

[DAVID CUTHBERT]

Phil,

I modeled your antenna, and if I did it correctly, the 350 uH lighting shunt inductor value can be substantially reduced. Even 35 uH looks good. This would allow 10X the lightning induced di/dt before the vacuum cap is subjected to enough voltage to arc. 1 kA/us will put 35 kV across the 35 uH inductor/cap versus 100 A/us with the 350 uH inductor. If you go this route I can calculate the physical stress on the inductor as the magnetic field pulls on the tower. We wouldn't want the inductor ripping to pieces. Also more attention to insulation is needed with a coil having less turns. #12 AWG THHN house wiring should be good for a transient voltage of 10 kV or more between turns. I have a 15 kV hipot power supply and can confirm this. 

     Dave WX7G