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Author Topic: Buried Coax Recommendations  (Read 1747 times)
KB9CRY
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« Reply #15 on: July 27, 2006, 06:15:14 AM »

A run of 2" PVC electrical conduit is cheap, easy to bury and will give you something to pull new runs of coax or rotator/control cables through"


In my opinion, 2 inch is too small.  You'd never be able to add any more cables and trust me, you will add some.


What about condensation?

Won't the PVC slowly accumulate water, such that the coax and rotator cables will be soaking in water all the time?
That can't be a good thing.



Yes, you are certainley right.  Condensation will get in via infiltration of moist air from the outside and the thermal cycling from day and night will cause the condensation.  In solid systems, they are pitched to one end and then a weep hole added to drain any condensation.

What I've done at my QTH is to use direct burial coax and installed it in 4 inch plastic, slotted drainage pipe which was also wrapped in landscape fabric prior to being buried.  The fabric keeps out the dirt and the slotted pipe continuously drains condensation.  The only way to keep out condensation from a rigid system would be to hermetically seal it after purging it with an inert gas like nitrogen.

Phil  KB9CRY
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KT8K
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« Reply #16 on: July 27, 2006, 06:32:00 AM »

I'm no professional, but helped bury some 4" pvc conduit at a club station years ago, and I remember it having drain holes we oriented to the bottom of the pipe.  We also put a little gravel in the trench under the conduit before we installed it.  That way condensation could drain off easily.  

We also put a large radius U-bend at each end, arranged so the opening pointed down, but we put these on after the initial cable run (threaded the cable through them), and did not cement them on so we could remove them if/when we needed to pull more cables (they fit tightly).  If this were a tower installation the coax should be connected to a grounded lightning arrestor (or the shield otherwise grounded) at the base of the tower anyway, so there shouldn't be much coax length to thread through the U-band in any case.

We first pulled about 4 strong cable-pulling cords through the conduit, and then used two of them to pull a couple of runs of coax through, leaving the others for future use.  As a last step I cut a couple of squares of hardware cloth - 3/8" mesh metal screen - balled them up and stuffed each one in an end of the pipe around the feedlines to keep mice etc. out.  If it were in my back yard I would probably paint the above-ground PVC a neutral color, medium/dark gray or brown for example - possibly to match the siding at the house end of the run, to help it blend in.

Like I said, I'm no pro, but what we did seemed to work, and we had no problems while we were using that setup.

I do advise putting in the best quality (low-loss) coax you can afford, though, at least the stuff with the non-contaminating vinyl jacket (like Belden 9251 or better).  I have found that type of insulation to last much longer than others in all my applications.

Wishing you many happy hamming hours!
Good rx & 73 de kt8k - Tim
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K9KJM
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« Reply #17 on: July 27, 2006, 10:32:15 PM »

Is this for HF or VHF/UHF?    If for HF, The top coax to use is Belden 213.  For VHF/UHF Times LMR-400 or better..........

I would put it in some type of conduit. Cheap flexible plastic water pipe is very low cost and will help protect it a LOT.  1/2" plastic will take a single RG-8 size coax, And is only about 5 bucks for a 100 foot roll. (Of course if you can afford larger diameter, That will allow for more coax runs in the future) Cheap insurance.  When you have your trench open, Be Sure to also lay in a bare copper wire for grounding/bonding OUTSIDE of the conduit.
I also install ground rods, Twice the distance apart as the depth. (8 foot deep rods spaced every 16 feet apart, etc)
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KD8BVJ
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« Reply #18 on: July 28, 2006, 04:57:33 AM »

I received my Bury-flex yesterday. I will be looking at the Home Depot this weekend for conduit. I may skip a weekend in my construction plans. It is suppose to be 90 degrees again Saturday.


              73
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AA4PB
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« Reply #19 on: July 28, 2006, 05:50:30 AM »

Don't forget - "swept 90s". They have a large radius making it easier to pull the coax around the turn. Also don't forget "conduit Phil". You will have a hard time pulling coax if you fill more than about 50% of the available conduit volume.

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KD8BVJ
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« Reply #20 on: July 28, 2006, 06:48:25 AM »

Thanks Bob. I can borrow a fish tape and I will be looking for conduit this weekend.
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WILLY
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« Reply #21 on: July 28, 2006, 11:26:19 AM »

 
KB9CRY and KT8K,

I thought condensation needed to be considered.  Thanks for confirming.   Thanks for the details on how you handled it too.

What about water in the ground, as if from a recent heavy  rain?  Wouldn't it get into the conduit through the weep holes?

Do you just let it, and assume it will quickly go back out and down?   And further assume that whatever amount of time that the coax is laying in water won't affect it anymore than it would be affected by being out in the weather?
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N3OX
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« Reply #22 on: July 31, 2006, 06:58:47 AM »

You got it!  While you might not want to immerse your coax in standing water for various reasons, coax is designed to not admit water through the jacket.  Direct burial coax is even better if it's going to sit in water for a bit, but it will eventually drain out through the weep holes.

I used 2" solid for a long time because I was in high school and a cheapskate and didn't need more than a few runs of rotator/control cable and a single run of RG-213 coax.  I used a remote coax switch at the far end to split out all the HF antennas.  The VHF antennas were on the house.  4" with weep holes is better engineering practice and more useful, for sure.

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KB9CRY
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« Reply #23 on: August 01, 2006, 05:06:49 AM »

What about water in the ground, as if from a recent heavy rain? Wouldn't it get into the conduit through the weep holes?

Yes


Do you just let it, and assume it will quickly go back out and down? And further assume that whatever amount of time that the coax is laying in water won't affect it anymore than it would be affected by being out in the weather?


Yes again, that's why I went with direct burial.  It's designed to be immersed in water.  My runs have been underground now for 6 years and no problems so far.

Phil
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KJ7BS
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« Reply #24 on: August 01, 2006, 01:09:54 PM »

You will have a difficult if not impossible time getting coax around a 90 degree bend unless you use RG-8 mini.  Use two 45 degree bends about 2 feet apart and use a good line to pull the coax through.  I've coated the coas with Ivory bar soap to help it go around the bends.

I burried105 feet of 2" PVC pipe from my shack to the rear fence of my property, where my tower and HF vertical are mounted.

Mark Saunders, KJ7BS
Glendale, AZ
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KB1LKR
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« Reply #25 on: August 08, 2006, 07:39:17 PM »

Or, probably better than Ivory may be wire pulling lube (Ideal, Greenlee, etc.) -- available at your local electrical wholesaler, Grainger, and likely even Lowes or Home Depot. As others have said, use large conduit and sweep ells -- all readily available in PVC electrical conduit.
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