Take those articles with a grain (or two) of salt. I see many of them
as a good guide for those who understand the circuit, how it works, and
what it's supposed to do. Over the years, I've found many errors in
construction articles.
Wires may not be rated for immersion, but coax, rotator control
cables and cables to remote antenna switches are hanging out in the
elements. Rain, Ice, snow, extreme heat and cold temps don't hurt them.
Ever look at a piece of CAT5 that's been on the tower for a while? Even
in the Northern climates, after a few years, the jacket becomes so hard
and brittle you can crush it just by squeezing it in your hand unless it
was specifically rated for exterior use. Now there is some cheap
cable! OTOH, I've had some rotator control cable do the same thing, but
the wires inside remained fine. It was purchased so long ago, I have no
idea as to its origin, other than it didn't come from a swap.
One time, one of the local hams picked up a lot of very flexible RG-8
size coax. (source?) The jacket was a gray, smooth, almost slippery,
soft plastic. It was almost as flexible as 8X, but after a few years in
Michigan's sun (43deg 37min N) it looked like it had a bad skin disease
and was covered with dark scabs. The chemical smell was very strong
(plasticizer?) I still have a few short pieces that were used indoors
and they appear to be fine, but they do have an odor, although faint.
Yes, with the pressure changes, mainly due to temperature changes, there
can be substantial condensation due to "breathing" (voice of
experience), but WHY CARE? What condenses, will eventually evaporate.
Sealing conduit is likely to cause ingestion of moisture unless all
joints are 100% sealed. I leave both ends open, yet after nearly 15
years, moisture has never been a problem. I used to drill little drain
holes at low spots, but I no longer do that. It seems to me to be a
waste of time. Besides, In the spring, around here a conduit a foot
down is likely below the water table. Sump pumps get a real workout in
the spring!
What difference would it make if the conduit were full of water as long
as there are no connectors, or splices in there and the coax is a
trusted brand?
73
Roger (K8RI)
On 1/28/2016 Thursday 9:17 AM, Al Kozakiewicz wrote:
QST is not peer reviewed. All kinds of nonsense can make its way into print.
The notion of copious condensation in buried conduit has always seemed like ham
urban legend to me.
First off, there are literally millions of miles of buried electrical conduit
in the world filled with wire not rated for immersion. The failure rate for
this infrastructure does not seem to be anything exceptional.
More important, condensation requires a constant supply of moist air. Where is
this supply coming from? Not convection, unless someone changed the laws of
physics while I wasn't looking. If there really is enough air flow from the
pressure difference between the ends of the conduit sufficient to bring in the
required moisture (unlikely), then seal the ends. Simple.
Al
AB2ZY
________________________________________
From: TowerTalk <towertalk-bounces@contesting.com> on behalf of StellarCAT
<rxdesign@ssvecnet.com>
Sent: Thursday, January 28, 2016 8:22 AM
To: tower
Subject: [TowerTalk] another subject: coax and cables buried or elevated
above ground?
My ongoing tower/antenna projects... hopefully I’m not boring others out
there...
I had planned on burying all lines to the towers (2, one at 150’ out and one at 300’ out) ... at first I
thought in solid joined (sealed) PVC which I can get for $9/10’ ... and I’ve also thought about direct
burial which for the coax and control cables has the added benefit of increased capacitance to ground and thus a
reduction of energy (lightening event) that reaches the shack... but control cables aren’t normally rated for
direct burial... or at least I don’t think so (researching that now)...
Then this latest QST article on coax says DON’T bury in any type of conduit be
it plastic or otherwise. It says condensation WILL get inside and ruin (flood) the
cables.
So .... if the cables are underground – below the frost line – say minimum 1’ down (upstate SC) ... how will condensation develop? Or
will it? I’m an engineer (HW/SW development) and reasonably intelligent but find it difficult to wrap my head around this issue... will it or
won’t it – flood that is? if it were always under ground – including both ends then I’d think not.... but it isn’t always
under as the ends come up to and above the surface... does that introduce a temperature variant enough to induce condensation? And I don’t like the
idea of holes in the plastic – that just means mud will indeed eventually work its way inside.
Maybe use corrugated tubing (again – no cuts or openings) ... this would allow
whatever moisture there might be, and I can’t imagine its going to be a great deal, to
settle in the lower points of the corrugation.
Comments from others that have been through this - in the south with similar
conditions would be appreciated.
Alternatively I could use a leader line and go from say 15’ on the first tower to the second tower and then that
same level to the shack with supporting 4x4 poles along the way... but this seems iffy as well as first the cables are
‘leaving’ the tower above ground potential so that might mean a higher voltage (common mode –
probably?) on the lines (again: lightening type event)... and the first tower is a rotating tower ... although thinking
about it that might work quite well to go from the tower with a ‘swing-arm’ of hanging coax/cables to allow
rotation.
thoughts?
Gary
K9RX
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
--
73
Roger (K8RI)
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|