On 4/16/2019 5:38 AM, Jim Miller wrote:
Is there some zener like ionization at the top that limits the voltage?
jim ab3cv
Supposedly, if you run a kW to a mobile whip on 80 meters, and the
whip has only a 1/4 inch metal ball on the top, you can get corona
discharge, like a Tesla coil. I have seen this problem fixed by
adding a copper toilet float ball atop the whip. Air has a
known electric field for breakdown, but it is a complicated
problem to calculate voltage by integrating the electric
field from the tip of the vertical to "infinity". If interested
in the details, see articles on Telsa coils.
A quarter wave vertical would have MUCH less voltage on top,
of course. If it's still too high, it is easily reduced by
adding a top hat.
I have a relay at the top of my 80 meter vertical. As
described in my QST article, I increased the spacing of
the contacts to 1/2 inch. I have never had any trouble
with this arrangement even at 1500W. Nor have any readers
of the article reported to me that their relays arc'ed over.
It is far easier to simply overkill the voltage problem
rather than attempt to determine exactly how much voltage
is generated.
Rick N6RK
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