Date: Sat, 27 Jun 2020 14:30:42 -0700
From: Dan Maguire <danac6la@gmail.com>
To: towertalk <towertalk@contesting.com>
Subject: Re: [TowerTalk] Do I need an insulator on the ends of my
dipole?
Jim, VE7RF, wrote:
>>> 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.
<A few years ago I did a little EZNEC study on that. Details here (Reply #16)
<https://forums.qrz.com/index.php?threads/touching-the-antenna-during-transmission.556342/page-2#post-4157410
<Dan, AC6LA
## Interesting. 40 volts rms at the center of the dipole, and 400 volts
rms, just 10% out from the center... and a whopping 1161 volts rms at the
extreme tips....and add 41% for peak V.
## I did try an experiment back in 1977, with a 204BA sitting on wooden
sawhorses in back yard. We stuffed a 600 w cxr into it.... and could
light up a
four foot fluorescent light tube to more than full brilliance ! The tube was
held a few inches away..and parallel to the tips of the DE. That was a dead
tube too, ready for the trash.
Neighbour was amused... no wires connected to the tube, yet it looked like a
500 watt bulb..and at 12 noon on a sunny, summer day.
Funny thing is, when birds, like starlings, sat on the tips of the els, on any
of my 20-15-10 m yagis....and with 1.9 kw cxr stuffed into the yagi, the
birds dont budge...go figure.
## In 1981, while trying to adjust the hb gamma match on a hb 10m
yagi...with wife in shack at front of house running the t4xc, I got a real bad
RF burn..and
I had leather gloves on ! That was the last time I had the wife operating
radio gear, while I was tweaking gamma matches. Next up, was tweaking the hb
gamma match
on a hb 20m yagi....at top of a 76 ft tower. Then I got some better help.
## I supplemented the .3125 dacron rope, used for guying both the 40m eles
and also the 80m rotary dipole..with small glazed egg insulators... in
compression mode.
This is where the dacron meets the ele. I was not about to trust the dacron
rope, when wet. I was not about to trust those egg insulators in voltage
standoff mode either,
so went with compression mode. Dacron used on both sides of the egg
insulators.
Jim VE7RF
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