Thank you gentlmen for your knowledgeable replies. I suspected this might be more complicated than dig and bury, and it can be given moisture, oxidation and ionic contamination by the soil, or rodent activity. I'll look for the DB suffix on coax, though I fear it might be something that might be only found at hamfests, not Home Depot. I got a 500' spool of RG-8 by Belden, but I wouldn't know it's archival quality for years. I guess the manufacturer may or may not know either, as the variables can be difficult to guage. Thanks again
Hello... I'm planning to trench and bury RG-8 (or something similar) but don't know if this will have adverse effects to the vinyl jacket. Does anyone know if there's a better coax for this intent, or can it work for 20 yrs.? Thanks for any ideas.
Figure about 8-10 years. Sun on the tower will deteriorate the jacket.
Moisture will be absorbed to some degree by the jacket and cause trouble.
Plasticizers in the jacket will bake into the center insulation and contaminate. Copper, Aluminum, Tin compounds will also contaminate the center insulation.
There is some advantage to running a 4" conduit, because it will allow you to replace the coax and allow the best life by allowing drainage and airspace.
Note that coax like 9913 and LMR cannot be allowed to get ANY moisture inside the jacket or there will be corrosion throughout the cable leading to broadband noise. If it is flexed around a rotor, the inside foil shield will be broken and contaminated by the outer shield.
Cables like 8214, RG-8 without foil shields do better around rotors.
It will help to paint the cable.
Of course, carefully assemble all connectors and tape to keep moisture out.
Beware, some antennas will leak moisture right through the connector ruining all your good work.
"RG-8" is a designation that's both extremely generic, and technically obsolete... this hasn't been a maintained military standard for a long time. Cables which generally meet the common meaning of "RG-8" might either do very well in a direct-burial application, or keel over and die within a short period of time... the devil is in the details.
What you want, if you want to do this, is a specific type of cable which is designated for "direct burial". These generally have a couple of important physical characteristics:
- The outer insulating jacket is "non-contaminating". It tends to resist the infiltration of water and other materials from the soil, which can otherwise contaminate the dielectric inside the cable and lead to high losses.
- It's often "flooded"... the interior of the braid/shield area is flooded with a sticky semi-liquid. If the outer insulation is damaged somehow (e.g. gopher-chew), the flooding material will prevent moisture from wicking into the cable. One specific variety of this sort of cable is LMR-400DB (the "DB" being, of course, "direct burial"). I'm sure there are others.
As a counter-example, I wouldn't recommend using 9096, 9913 or any other air-dielectric cable, unless you're willing to go to the trouble of pressurizing it with dry nitrogen for the next 20 years :-)
I suppose that another option is to run a buried, waterproof conduit, and then run coax through the conduit. I'm not sure that this would work out any better than direct burial... keeping the conduit leak-free, and free of condensation from atmospheric "breathing" is difficult.
--
Dave Platt AE6EO
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Why not get the same cable the Cable Companies use? I live in a rather wet country,(NL) and those cables have been in the ground for more than 20 years here.
Of course 7/8 hardline DB would last 20 years if nothing chewed it, but will you live where you are for the next 20 years? Is it worth spending so much more? Large conduit and less expensive coax is most cost effective and allows expansion of the station. Unless you are really going to run more than 100' then surplus TV hardline becomes attractive.
yes, place the coax inside PVC drain pipe at the top of the tube, do not lay it on the bottom. Arch the pipe slightly so that drainage is out to the end(s) of the pipe. Place an access point at the end with an inverted chamber. Think of the construction as though the whole thing is under water, and any moisture that gets in has a path out, construct it like that, and it will last longer than 20 years, and not cost too much, just require some careful efforts.
Les I did a bit of checking and found that coax for burial is called wetted it contains a wetting agent in the pvc covering intended to keep out moisture and protect the braid from water infiltration. I suspect it probably has a silicon oil or other silicon compound intergrated. If you do a search for this type you will find its is readily available from many sources including lots of sattelite suppliers.
About the only type you would get from a hamfeast is heliax and I doubt you want to keep a bottle of nitrogen hooked up to it all the time.
A local Belden, or Times Microwave distributor might be your best bet.
Or, order it from
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or a similar mail-order distributor.
Belden seems to use the WB suffix to indicate flooded, water-resistant cable, suitable for burial. 7810WB is a low-loss RG-8 type with those characteristics.
If it'd designed for direct burial, the manufacturer can almost certainly tell you.
If it isn't, they may say "Son, you're on your own!"
--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
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