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[TowerTalk] Coax in Conduit and WATER!

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Subject: [TowerTalk] Coax in Conduit and WATER!
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Date: Mon, 7 Jul 1997 09:04:11 -0400

---------------------- Forwarded by Tyler G Stewart/BENN/CEC on 07/07/97
09:04 AM ---------------------------

Tyler G Stewart
07/07/97 09:03 AM

Subject:  Re: [TowerTalk] Coax in Conduit and WATER!  (Document link not

While I direct-buried my hardlines to my first tower, I also buried a
length of the 4" corrigated drain pipe as a conduit for any additions I
might want to make later, as well as some runs of RG8X I use for RX
antennas.  It's been QUITE handy and the stuff is very inexpensive and easy
to work with, being so flexible.  I used the"solid" type without the slots
for this run.  I've noticed that
it does have a little water in it.  It's on a slight grade, emptying into a
basement window well, so I dont think there is much, but the cables do come
out wet.

I'll be digging a new trench to my next tower in the next couple months
sometime, and I think I'll try running the slotted stuff and see how it
works out...or maybe one of each.  It will also be on a downhill grade, so
it may not be a very good test.

At any rate, the black corrigated drain pipe makes a very nice, inexpensive
conduit for smaller cables, and I'm sure you could pull hardlines thru it
if you put a "bearing" on the front end of the cable so it didnt get
snagged on the walls.

73, Tyler K3MM on 07/06/97 11:45:23 PM

Please respond to

cc: (bcc: Tyler G Stewart/BENN/CEC)
Subject:  Re: [TowerTalk] Coax in Conduit and WATER!

John Brosnahan wrote:
> At 05:15 PM 7/6/97, you wrote:
> >>>  It wasn't that good and we ended up
> >locating all
> >of the splices with the help of a TDR, digging them up and redoing them
> >. <<
> >
> >Gee... If you really mean hardline (and in radio astronomy I believe
> >that you mean real hardline -- frequently run with refrigeration lines
> >for the low noise head) you would think that there would be a high
> >quality dehydrator circulating and constantly drying the air (or other
> >gas) that becomes the dielectric in the transmission line.
> >
> >Joe / W8SS
> Yep, I mean hardline--basic foam-filled 7/8 inch, 100 ohm stuff that was
> surplus.
> Not all radio astronomy is at microwaves.  We did a lot of HF and low VHF
> radio astronomy--primarily Jupiter--Io effect and solar emissions.
> Sky background was the limiting factor.    This was a low budget
> hence the ammo boxes to protect the splices--but it this case the
> was the problem.
> John  W0UN
> --
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I had a similiar experience at work.  A moderate size multi 10 KW HF
site, all antenna feed lines 1 5/8" Andrew foam.  Because of orginial
design specs,all feedlines were run in 2 1/2" black iron pipe.
This was for EMP protection, and other considerations.
When we installed a new larger size cable vault and some other upgrades
two years ago I noticed all feedlines were full of water.
Water poured out of the conduits when we broke them open.  The water
just migrated through the foam dielectric.  Turned the copper inner
conductor and outer conductor sheath in the Andrew cable green.
I have been told by several professionals in the tower trade
that yes even PVC conduit catches and retains water. Even the local
(to me) Andrew Antenna marketing/engineering manger confirms this.
Some even suggest the drilling of weep holes on the underside of the PVC
and to run the conduit with a pitch to it so water will not stand.
I often wondered if using 4 inch perforated black irrigation pipe
(comes in 100' foot rolls and longer) with the pipe back filled in
either sand or crusher run stone would drain?  It is cheaper than
electrical conduit.  Then you have the best of both worlds, a
path where replacement of feed lines can be done, additions made,
and a system perhaps drier(?) than solid wall conduit.
Even with direct burial of hard line, most vendors (Andrew for one)
suggest that the backfill be sand, not the orginial material removed
when trenched.
Dan Szymanski
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