Gary,
Some of my coax cables and control lines are in plastic
conduit and I've never had a problem with condensate.
I use 4" PVC, 200 ft run with homebrew concrete access
boxes at the ends and one in the middle. To avoid the
condensate issue, I installed a Tee at each end and "screened"
one of the ports on the Tee to allow air to circulate through
the pipe.
The only change to I would do is to add several smaller plastic
tubes inside the 4" tubing so that any added cables wouldn't get
tangled around existing cables.
As for direct bury of control cables. I've never had an issue
with my ordinary 8-conductor rotator cable, and what the
telephone industry calls "station wire"...the skinny 4-conductor
cable normally used in residential wiring.
I also have ordinary RG-8U that's been direct buried for more
than 30 years. I recently did a freq sweep of that cable and
the loss is still in specs!!!
73,
Charlie, N0TT
On Thu, 28 Jan 2016 08:22:36 -0500 "StellarCAT" <rxdesign@ssvecnet.com>
writes:
> 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
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