[TowerTalk] Orion 2800 Rotator Cable Replacement

[Bob Shohet, KQ2M]

Hi Jim,

”A major advantage of using stretched wire is that un-stretched copper 
will stretch under tension over years. Before changing to stretched 
wire,”

I have seen you mention this a number of times in the past and I have been meaning to ask you some questions about it.

My non-engineering understanding of wires and stretch is that a given wire after being subject to variable strength forces over a given period of time, will stretch only so far before it breaks.  Assuming that that is conceptually correct, let’s say that we have two wires – Wire A and Wire B.  Wire A has been pre-stretched before being put up and is now compared against Wire B which has just been put up without being pre-stretched

Now we subject both wires to the same forces over the same period of time.  I would expect that going forward Wire A will not stretch as far as Wire B, but is more likely to break and break sooner under significant force than Wire B because it has already been pre-stretched.  Wouldn’t this be correct?

If this is not correct, can you please explain why?

Tnx & 73

Bob  KQ2M


From: Jim Brown 
Sent: Tuesday, December 10, 2019 4:49 PM
To: towertalk at contesting.com 
Subject: Re: [TowerTalk] Orion 2800 Rotator Cable Replacement

On 12/10/2019 1:13 PM, john at kk9a.com wrote:
> Of course I meant to say "with no issues" in my post.  The nylon coating on
> THHN does quickly deteriorate outdoors however I believe that the nylon's
> purpose is to lessen friction and improve chemical resistance. Neither of
> these are issues to me and the PVC underneath is pretty tough.

The 350 ft run to my Yaesu rotator are two 250 ft runs of #14-2 Romex 
(plus ground) to the base of the tower, laying on the ground. 
Transitioned to something smaller to go 120 ft up the tower. Nine years 
so far with no issues.

I've used THHN extensively for wire antennas and radials. My current 
favorite for high dipoles is bare #8 that is stretched to make it hard 
drawn #9 -- attach one end to a fixed object and the other to the 
trailer hitch on the SUV, pull slowing until it breaks.

A major advantage of using stretched wire is that un-stretched copper 
will stretch under tension over years. Before changing to stretched 
wire, I found that I had to circumcise my 80M dipoles (#10 THHN) every 
few years to keep them on frequency. For my fan dipoles, I now use 
stretched wire for the longest element that bears the pulling stress and 
THHN for the shorter elements that do not.

73, Jim K9YC


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