Topband: how high are very high voltages on antennas?

[Rick Karlquist]

Grant Saviers wrote:
> It is often mentioned that "very high RF voltages" are present at ends
> of dipoles, voltage nodes on loops, etc. but I haven't been able to find
> any guidance in the form of numbers.  How high is "very high"?  Assuming
> QRO power into a full size apex up delta loop, corner fed, vertically
> polarized, what will be the voltage at the apex?  I haven't found a way
> as yet to have EZNEC give me a value.
>
> If I wanted to put a relay at a voltage point to switch a stub, how
> would I float the 12v DC coil from the RF present?
>
> Grant KZ1W

I used to have a 130 foot end fed wire.  At 1.5 kW, it had
over 2,000 VRMS on 80 meters.  I used a fixed 120 pF vacuum
capacitor and a 6 inch diameter coil as a matching network.

If you use a big 240VAC, 30A contactor, you shouldn't have any problem
with the coil having enough isolation.  You can increase the
spacing of the contacts to get more voltage rating using the
technique I described in May 2009 QST page 66.

Rick N6RK