[TowerTalk] another subject: coax and cables buried or elevated above ground?

[N2TK, Tony]

Here in upstate NY I had planned on using PVC when I buried my cables. I quickly found out that in many places I could not dig down below a foot without hitting solid rock. And there was no way I could dig a straight line because of the rock ledge. The path of the trench looked like I was drunk when I dug it. So I dug a 1' deep trench where I could to go from the tower to the house. I put about 6" of sand in the trench. Then I put in the coax and control cables.    Filled the trench with sand and let the grass grow over it. 
Last year I pulled up some grass to just check on the cables. Everything seemed to be fine after 20 years.  May want to add a couple RG6 lines in the trench this year. It should not be too hard to do that.

But I did have a problem when I first buried the cables. I had a run of 70 ohm 1/2" bare aluminum hardline in the trench. After three years the soil near the house had made the aluminum jacket mushy. Most of the shield was etched away. I have had no problems with PE jacketed cables.

If I could I would have used PVC. Make sure you use  large enough PVC in case you want to pull more lines later on. And/or run two PVC lines in parallel for future additions. 

GL
N2TK, Tony

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of StellarCAT
Sent: Thursday, January 28, 2016 8:23 AM
To: tower <towertalk at contesting.com>
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
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