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Re: [TowerTalk] Outdoor Coax Issue

To: jimlux <>
Subject: Re: [TowerTalk] Outdoor Coax Issue
From: "Roger (K8RI)" <>
Date: Sun, 02 Nov 2008 16:23:49 -0500
List-post: <">>
jimlux wrote:
> Ri
>> Can I just bury this about six inches down without worry.
> Are you subject to electrical codes? Or, more to the point, do you want 
> to be code compliant?  If so, you'll have to bury it substantially 
> deeper. You'll have to check your local rules, but in general, there's 
> one depth for unprotected cables, another for cables in conduit, and yet 
> another when there's concrete over the top of it.
Another question is there any traffic through the area and what kind of 
There are not many cables I'd bury only 6" where there was a lot of 
traffic overhead.

Here unprotected cables must be 18" or deeper AND covered with a 2X4 or 
larger equivalent. BUT that is for power cables.  There is no reg 
covering coax, rotator, or control cables. BUT YMMV as it depends on the 
inspector who might check it out and of course those regs vary widely 
from local to local.  Locally ham towers (100' and under) and stations 
are pretty much exempt from most of the code.  My grounding system was 
to code when installed, but since then they have increased the size of 
the grounding cable required.
>> If so, Do I need to pull it up and replace it in X years... and
>> if so, can you solve for X?   What is the useful life of this
>> type of coax?
Replace coax when it needs it, not by schedule.
There are a number of "buriable" cables and then there is "direct bury". 
They are not the same although the use if pretty much the same. The 
lifetime is determined by the jacket material's chemical composition, 
its physical properties, the consistency of the soil (stony versus sand 
and/or clay) and climate (freeze thaw cycles and temperature). With good 
sandy or clay soil buriable cables will work fine, but "Direct bury" has 
a compound inside the jacket that permeates the braid. (Really gooey 
stuff!) which prevents water from migrating or doing damage should the 
jacket be perforated. That's for the rocky soil, including gravel and 
particularly those soils where the freeze/thaw cycle is present. 

Davis Bury-Flex, which gets mentioned on here quite often, doesn't have 
the compound, but they mostly make up for it with a very rugged jacket. 
So, "in my estimation" it'd make a very good cable to bury (it is called 
Bury-flex) except in extreme conditions. I wonder what the market 
potential would be for a Bury-flex version containing the "direct bury", 
or flooding compound, or one that would be a flexible match for 
LMR-600?  My guess would be the extra expense and small market would 
make them uneconomically viable.  But who knows, the military uses a lot 
of LMR-600UF which has a notably short life.  All the RG-6 I purchase is 
flooded and because of the vast quantities in which it's produced the 
price is low. Even with the cheap F-connectors water is not a problem 
although I use the water proof,  compression connectors for good 
measure. That and they are easy/fast to inst all as well as providing a 
much better mechanical connection than the cheap ones.

I have, over the years, direct buried many kinds/brands of cable.  In 
"good soil" (IE that where stones are absent) some cheap cables will 
actually last longer than when exposed to the sun and elements IF the 
jacket is not permeable to water AND we are not talking about desert 
floor where you could fry eggs.  However I'd recommend staying away from 
the cheap cables often found at swaps. 

It seems as if many swaps bring out "Cheap" *stuff*. (I'm being 
charitable).  I used to stock up on connectors at the local swap but 
doing so required care and a lot of inspection.  The problem with 
purchasing "on-line" is not being able to inspect the connectors, but 
they generally list the materials used in construction.
> If you DO have to pull it up, that's when having some conduit makes life 
> a LOT easier.  A run of 3" conduit with nice sweep bends at the end is 
I use a pair of sweep 45s which gives the 90 degree turn an even wider 
A word of caution, when installing conduit it is desirable to fully seat 
the sections. IOW, after coating the mating surfaces with the sealing 
compound they become very slippery for a VERY short time.  Make sure the 
one is inserted all the way to the inside shoulder.  This makes pulling 
(and pushing) cables much easier as there are no shoulders to catch the 
cable, or at least any left are quite small.  It can be very frustrating 
to pull in 75 to 100 feet of cable and hit  a shoulder (you can't get 
past) just a few feet from the end.   Properly taping the cables into a 
bundle that tapers to a point and using lots of cable pulling soap helps 
to eliminate this, but pulling a wad of cables with connectors can make 
for a rather inflexible section of cable where these can create problems.
> easy to pull coax through. Easy to pull the coax out part way to check 
> the condition too. Plastic electrical conduit isn't all that expensive, 
> and since you have to dig the ditch anyway...
And use wire soap.
I have two conduit runs that are pretty well protected and about 18" 
deep. The one to the house/den is about 75' and the one to the shop is 
only about 35-40' Using wire soap (Liberally) I was able to *PUSH* two 
runs of LMR-600 and three control cables through.  I had to pull out the 
old cable from the one to the den and that came out easier than dragging 
the same length across the yard.  Using a 3/16" nylon pull line, I, or 
rather my wife pulled in  two runs of LMR-600UF (I found a protected 
place for it) along with two control cables. I was busy soaping the 
cables as they entered the conduit at the tower.  Her comment as the the 
liberally soaped cables coming up out of the conduit...Euch!
> I wouldn't obsess about the water in the conduit thing.  Your conduit 
> will be water tight where it's underground, so the way water gets in is 
> through "breathing" and atmospheric moisture condensing.  If air can get 
> it for condensation, air can get in to evaporate it too.
And many times drainage is not an option.
> By the way.. whatever you wind up doing, take an antenna analyzer or 
> similar, and make a bunch of measurements of the loss of the coax at 
> various frequencies.  That way, when your receiver seems deaf or the Tx 
> isn't getting out, you can recheck the coax without having to dig it up 
> or pull it out.
Knowing what the characteristics of reach run are is a very good idea. 
Coax improving with age because the SWR is going down is the wrong 
conclusion. <:-)) What would really be nice would be a Time Domain 
Reflectometer (TDR), but those are well beyond the reach of most of us.  
When I was working in instrumentation I was able to borrow (sign out for 
the week end) some very nice equipment including a spectrum analyzer and 
TDR.  The only thing missing was a sweep generator that I could use on 
the two meter band to set up cavities.


Roger (K8RI)

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