[TowerTalk] Buried HF/VHF feedlines

[Dave Sublette]

I ran two runs of 7/8 hardline underground (in KY) for 30 years with no
problems.  The cable was buried only 6 inches or so, just enough to get it
under a mower.  It had a low spot-- perhaps three feet low or more in the
middle.  The run was 250 feet.  It froze and thawed every winter. Water
stood on it after a hard rain. I didn't have the severity of freeze/thaw
temps that you have, but I never had a problem.  I ran every frequency from
40 meters through two meters and had great success.  It was used when I put
it in and measured better than factory specs when I took it up three years
ago.

Dve, K4TO

On Sat, Jul 25, 2020 at 4:03 AM David Gilbert <ab7echo at gmail.com> wrote:

>
>
> Heliax is essentially plumbing.  Quite possibly I simply don't
> understand, but why is water a problem?  How does it penetrate the
> copper sheath?
>
> And if water is a problem, why can't you have a hole in the conduit at
> the low spot to drain off the condensation (assuming you're below the
> frost line)?  The condensation should develop rather slowly, I would
> think, because it requires water vapor to penetrate the conduit.
>
> Like I said ... maybe I just don't understand the situation.
>
> 73,
> Dave   AB7E
>
>
>
> On 7/24/2020 11:17 PM, Jonathan - KE0YBL via TowerTalk wrote:
> > Hi All,
> > I feel like this has been done to death - and yet, the Internet has
> really been notoriously awful with misinformation for me the past few
> weeks. I appreciate your thoughts as I work through this!
> >
> > I'm putting up a new tower primarily for HF and maybe some VHF. Given my
> ideal location is some ~350ft+ from the shack, I've been waffling back and
> forth as to whether to remote the radios in an enclosure, or bring Heliax
> back. I'm leaning toward the Heliax route.
> >
> > I'm working with an experienced (decades) climber/tower company in my
> area (Minnesota), who has used 7/8" Heliax for $1.50/ft. This seems
> reasonable, and a fraction of new, thus making my project seem doable.
> Sadly may require an underground splice due to lengths, but one battle at a
> time. I'm open to other sources for such things.
> >
> > Herein lies the rub -- my climber's experience has been (and probably
> yours as well) that directly burying this in our frozen tundra eventually
> results in crushed cable through thawing and freezing. I'm considering 3"
> or 4" HDPE conduit/innerduct to alleviate that, but given I'll need to go
> through a valley, condensate will condensate in the dip no matter what I
> do. I could perhaps drop the conduit down 36+" deep to avoid the frost
> level, but it'll still be sitting in water (albeit not frozen at that
> depth) without active moisture management in the run (fan, nitrogen (ugh),
> whatever - not feasible).
> >
> > I feel like at this point I'm really overthinking it. Fiber to the tower
> and radios in a box would be much easier, but less desirable - but now I'm
> really torn.
> >
> > I appreciate your feedback immensely,
> >
> > Jonathan
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> >
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