Your local soil conditions may be the determining factor. I live in
central Maine at 45.2 north latitude, with sandy soil. There is a lot of
broken glass and other junk in the soil which I was worried about. Since
2006 I have had 250 feet of heliax (LDF5-50A) running on and directly
buried in the ground. About 100 feet is laying on the ground along a
line of trees. The remaining 150 feet is buried, never more than three
inches down and sometimes less. When I buried this stuff I tried to
surround it with a couple inches of fresh, clean sand to help keep glass
and stuff away from it. I don't know how successful that has been over
time, but so far so good.
Obviously the ground freezes every winter. Drainage of this sandy soil
is excellent when not frozen but in winter it is not uncommon to have
several inches of ice built up on top of the soil under the snow pack.
Where the heliax comes out of the ground to go up the tower it is frozen
in a few inches of ice every year. I have yet to see any sign of
physical damage there. Portions of the 100 feet that run on top of the
ground are subject to similar ice conditions.
There is one home made splice in the buried section. It is well
waterproofed - hot melt adhesive lined heat shrink tube, then a double
or triple layer of Scotch 23, then a triple layer of Scotch Super 88+.
This was old heliax when I installed it. 19 years later it is still
working well on 2 meters and swept well on return loss last summer. I
have not measured the loss recently but have no reason to suspect
anything is wrong with it.
This has been my experience in a cold climate. Your results may differ.
I also have a couple of 100 foot runs of heliax, several runs of CATV
hardline and a run of 9913-equivalent running to another tower through
PVC conduit, but I have that sloped so any water that gets in should run
down hill the whole way and out the other end. It sounds like that is
not an option in your case.
73,
Paul N1BUG
On 7/25/20 2:09 PM, Jonathan - KE0YBL via TowerTalk wrote:
Thank you all for taking an interest in my project. To address a couple of the
questions that were asked:
- I live in Minnesota - fairly cold.
- The valley I need to run through is known to have sitting water in the spring
and the fall, and is probably saturating multiple feet down. I'm necessarily
concerned with that (as you've all said, the cable is water-tight). This makes
me hesitant to use any type of irrigation line (given ground saturation in that
area). Presumably with SDR13.5 HDPE conduit, all I need to do with is temp
differentials introducing condensation.
- I plan to have at least a couple runs of cable - not entirely sure I'll break
things up yet, but it does increase the costs. Still waffling on that aspect a
bit.
- I've not seen new costs near $2.40 that were mentioned by Jeff WN3A. Online
sources I've seen appear to be nearly 2x that, which seems like a disparity.
I'm in MN, bit too far to drive, but I'm open to alternative sources/shipping.
I'm not sure the brand/specs on the cable my climber has. I know he regularly
uses it on his own 2-way customers, but was reserved about details (perhaps
un-intentionally).
Thanks,
Jonathan
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, July 25, 2020 12:17 PM, Rik van Riel <riel@surriel.com> wrote:
On Sat, 2020-07-25 at 06:17 +0000, Jonathan - KE0YBL via TowerTalk
wrote:
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).
If you go with 4" irrigation pipe (schedule 80, I believe),
the home improvement stores will sell you pipe segments that
have holes in the side for water to drain out, and "socks"
to put around the pipe so dirt doesn't get in.
It would be easy enough
to have some of the segments in the
dip be ones that let water out.
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