re #3
I use a pull down line of parachute cord tied to the hoist line on the
pull side of the insulator so when something breaks - wire, coax, or
insulators I can retrieve the hoist line top end. Or, make the hoist
line a loop with a short tail for the insulator, but that takes a bit
more of the larger, more expensive line and can be confusing to the
ground crew.
The CMI pulleys are great, I use them for rigging stuff. For wire
antennas, I use marine ball bearing blocks (single sheave pulleys) which
substantially reduce the friction and line wear (smooth, never jam, last
forever, and the line runs straight with their swivels). About $15, if
you shop around on the web for Lewmar, Harken, or Ronstan. More
expensive at West Marine, in my experience.
Grant KZ1W
On 8/6/2017 13:23 PM, Jim Brown wrote:
I use water jugs (don't remember capacity, only weight) filled with
dry sand. They weigh 95 -100#, which is my estimate of the tension on
a centerfed horizontal wire. I use CMI rescue pulleys and mostly
5/16-in Synthetic Textiles rope. On the longest run that's under the
greatest tension, I use 7/16-in rope. Both ends have pulleys. On each
antenna, one end is tied down, the other end has the weight.
In my 11 year experience with antennas in these tall trees, the
failure modes are
1) Wire connection/tie-off points (solder is bad, loops through eyes
that double back on the wire and split bolt connectors to secure both
electrical and mechanical connections are good. A good rule is to
never solder a connection that will be stressed -- eventually the
stressed wire will break at the soldered connection.
2) Wear on the support rope where it goes through a pulley. That's why
I use 7/16-in for the longest, highest antenna.
3) Poorly made center insulators. Even with the best, I've learned to
add rope across the insulator so that the dipole doesn't hit the
ground if the insulator fails. (Getting two ends of a dipole up that
high costs at least $800 for a day's worth of a guy in the trees and a
helper on the ground. The last thing I want is for them to come back
for something in the antenna that broke, releasing one or both support
ropes so that the pulley must be re-strung. Ask me how I know. :)
73, Jim K9YC
On 8/6/2017 12:44 PM, Clay Autery wrote:
Roger that, Jim. Until I can get my ENTIRE loop path clear of
vegetation, I will have to accept the trade-off and continue to use the
insulated stuff. (Maybe this winter, fingers crossed). Since I can
pull the entire loop down in about 10 minutes, keeping it pruned to
tuned length isn't much of a task... Mine aren't nearly as high up as
yours. :)
I'd love to give the bare solid stuff a try... How much weight do you
have to use to keep it tensioned in the air? 280+ feet of #8 would be
some bit heavier...
And I'd definitely have to come up with a bigger diameter pulley. :)
______________________
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389
On 8/6/2017 1:40 PM, Jim Brown wrote:
The problem with using ordinary copper wire for antennas where the
wire is under tension is that it stretches. Mine high dipoles are
under about 100# of tension (up 140 ft, fed with RG11), so every few
years, I have to let down my 80/40 dipole that's built with #10 THHN
stranded and circumcise it to keep it on frequency. I've since
migrated to using #8 bare solid copper that I've stretched by tying
one end to a tree and the other end to the trailer mount of my SUV and
pulling slowly until it breaks. The result is close to being hard
drawn, roughly AWG #9, and about 15% longer. Antennas that I've built
with this seem not to stretch. Over the years, W6GJB and I have done
this with at least 2,000 ft of #8.
73, Jim K9YC
On 8/6/2017 10:44 AM, Clay Autery wrote:
Correct... THHN is not intended for use as exterior antenna wire, but
it surely does work well... I can get it in any color I want and in a
2500+ foot spool, et al.
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