[TowerTalk] Do I need an insulator on the ends of my

[Jim Thomson]

Date: Sat, 27 Jun 2020 14:30:42 -0700
From: Dan Maguire <danac6la at gmail.com>
To: towertalk <towertalk at 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