On 6/27/20 8:19 AM, Jim Thomson wrote:
Date: Fri, 26 Jun 2020 21:33:25 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Do I need an insulator on the ends of my
dipole?
On 6/26/2020 11:07 AM, Kevin Zembower via TowerTalk wrote:
Why do I need an insulator?
<Because the open end of an antenna is a high voltage point, and when the
<rope that holds it is wet, the RF can melt it and the antenna will fall
<down. Ask me how I know. :) If instead it's connected to an insulated
<wire, because it's a high voltage point, the insulation can arc over to
<the wire. The same is true of radials.
<73, Jim K9YC
## Does anybody know what the EXACT peak voltage is....on the ends of a half
wave dipole,
say with exactly 1000 watts cxr applied to the feedpoint ??? Say a 80m
dipole up 100 ft... flat swr, fed with coax + CM choke.
It's difficult to measure or calculate. And it is almost certainly
limited by corona discharge (3kV/mm of radius on a clean smooth conductor)
In an idealized sense, one can look at it like a 1/4 wave transmission
line, but since it radiates, it's not.
## what is peak Voltage at various points along the dipole ?? again with 1
kw cxr applied. What happens to peak V along the dipole as swr is increased
?
Interesting question. For "small" changes in length, even though the
feedpoint reactane gets big, I would think that the voltage distribution
doesn't change.
But for large changes (an electrically short diple)
## I would have thought rain water was distilled water, high resistance...
but have never tested rain water.
Have tested store bought distilled water..and then compared distilled water
to tap water.... huge difference.
Rain water is pretty clean although it can have dissolved gases in it
(e.g. Acid Rain downwind of areas burning high sulfur coal)
The rope, though, is almost certainly not clean - at first. If you get
enough rain, then it probably washes off.
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