[TowerTalk] Wire antenna in trees? (Patrick Greenlee) (Kelly Taylor)

[Jim Brown]

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.