[UK-CONTEST] Supporting an overhead run of Heliax

[David Aslin]

Alan, 
Heliax on a catenary is common practice in California, where the ground
is often too rocky for economic trenches.  See for example:
http://www.wc6h.com/gallery/v/wpx2008/P1010492.JPG.html where I've guest
operated several times.  Rich's rotator cables and feedlines have been
on these catenaries for at least 6 years through snow, ice, wind and
blazing sunshine.  The trick is to loosely fasten the Heliax to the
catenary (just tight enough to hold it close to the catenary wire or
rope, but not tight enough to distort the cable) and support at frequent
intervals with UV-resistant ty-raps or tape.  You'll need to inspect the
ty-raps/tape say annually since their UV resistance is far from perfect.
But still cheap to replace from time to time - much cheaper than digging
a trench and putting in conduit!  If the catenary is under good tension
and you have expansion bends/curves in the Heliax at the ends of the
catenary, all should be OK and the effects of any sway will be minimal.
In the WC6H case, the catenary runs from each of the towers to the eaves
of the house (single storey, so about 10ft high) with turnbuckles to
tension them, so sag is pretty small.  Distance from tower 1 to house:
about 100ft; tower 2 abt 60 ft.  With your longer run, maybe the trees
would allow the distance to be covered in two shorter runs? 
N6RO uses a fence post to support the feedlines from his 15m tower part
way along.  http://www.jazznut.com/n6ro/N6RO%2015M%20STACK%201.JPG You
can also just see the feedlines for the 20m tower at the bottom of this
shot: http://www.jazznut.com/n6ro/N6RO%2010M%2020M%20STACKS.JPG 
Hope that helps a bit,

73
Dave G3WGN WJ6O

-----Original Message-----
From: Alan Ibbetson [mailto:alan at g3xaq.net] 
Sent: Saturday, January 15, 2011 8:59 PM
To: uk-contest at contesting.com
Subject: [UK-CONTEST] Supporting an overhead run of Heliax

I want to run 160ft/50m of Heliax across a field to my second tower. I 
have some LDF2-50 or LDF4-50 I'd like to use. The ground is a long way 
from being flat and anyway I'm too tight fisted to fancy installing a 
buried cable duct.

There are a couple of handily placed oak trees nearby. I was wondering 
whether anyone has experience of supporting this much Heliax and a 
rotator cable from a wire rope catenary?

Info on the web suggests a 100lb "bucket of concrete" will tension the 
rope adequately with only about 6ft of sag, which will be OK with the 
ends 20 or 30ft up the trees.

I have two questions: will the Heliax fail with stress cracks from 
swaying about in the wind; and is there a hidden catch I've not even 
thought about?

73 Alan G3XAQ
-- 

Alan Ibbetson
alan at g3xaq.net