>> 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
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.
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