Jeff:
Given that you have a short (20 foot) length of coax between your tower
and shack entrance, your installation is very similar to most commercial
installations on towers. In those cases, the coax shields are grounded at
the tower tops and bottoms, much as you're proposing to do. The lightning
arrestors are mounted on the shelter/shack entrance panel (typically copper,
but Hams can and do use aluminum) which is grounded to a nearby ground field
(consisting of more than a single ground rod.)
However, I would caution against exposing arrestors to weather. The
Polyphasers I have in my tower installation don't seem to have any kind of
gasket material between the access panel and the rest of the alunimum box.
So I chose to install the arrestors in a steel cabinet at the base of the
tower. You ought to consider installing a similar steel box where your
conduit system emerges from below ground to penetrate the side of your
shack. There, you can transition from underground coax to the SPG (single
point ground) panel and arrestors, thence into your shack with additional
coax lengths.
For my conduit I chose gray 3 inch PVC electrical conduit, available
from electrical supply stores. If I had to do it over again, I would have
selected 4 inch. At bends I installed sweeps rather than elbows. The
elbows are too sharp a turn for stiff coax, especially hardline, to be
pulled through. The sweeps are larger radius pieces that attach just like
elbows, but they provide a gentler curve through which the coax can be
pulled more readily.
Here is a link to Scott KA9FOX's tower installation pages:
http://www.qth.com/gallery/v/ka9fox/KA9FOX-Trenching/ . He used a similar
technique to house his coax arrestors in a steel enclosure outside his
shack. Here's another approach, by N3RR
http://users.erols.com/n3rr/lightningprotection/index.htm . Finally, here's
a link to some photos of my own installation. The steel box outside the
shack is shown just above the SPG angle piece that is inside it. I have
also written a note here
http://lists.contesting.com/archives//html/Towertalk/2007-10/msg00356.html
on home-bewing a ground clamp for coax shields.
Hope this helps.
Gene Smar AD3F
----- Original Message -----
From: <kb2m@arrl.net>
To: <towertalk@contesting.com>
Sent: Wednesday, January 20, 2010 8:59 AM
Subject: [TowerTalk] coax entry
> I'm building a new home that will have a full basement. I'm going to move
> my
> shack into the basement and I'm looking for any ideas on how to bring in
> all
> my antenna cable's. I have about 12 antennas total. Cable's will consist
> of
> mostly RG-8, but two of the cables are hardline, one 1/2 inch, the other
> 5/8. The new house will be about 20 feet away from my tower.
>
> I was thinking of mounting a grounded plate to the tower, and then attach
> all of the cables. I would also mount lightning suppressers at that
> location. I would then run short 20 foot cables into the shack via a
> buried
> conduit. What should I use for the conduit? Does mounting (and grounding)
> all the antennas to the Tower make sense, or should I do this just outside
> the house? Any and all input appreciated.
>
>
>
>
>
> 73 Jeff kb2m
>
>
>
>
>
> _______________________________________________
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