Running Heliax out of doors

[Panrock]

I am helping with an installation where it will be necessary to run Heliax LDF4/50 feeder over some distance, out of doors.

How weatherproof is it considered to be? Can it even be covered by soil? (I am not proposing to test it with a garden spade!)

Thanks,

Steve

[Radio Wrangler]

It is seriously weatherproof and the proper connectors have compression seals, but it's best to protect them further.

Do not bury directly, it can be crushed and shorted. It can be run inside something which gives mechanical protection, though. So some bury-able duct piping is needed. though alkathene water pipe or gas pipe works, but you need to put marker tape over it to warn people it isn't the water or gas pipe they're looking for!

David

[Panrock]

Seriously helpful. Thank you!

Steve

[GrimJosef]

Depending on your local details (depth of burying, height of water table, rain percolation etc) there's something to be said for running a single continuous length of protective pipe. If the average tendency of water is to leak into the pipe rather than out of it then even with the smallest leak, say through a joint, it will eventually end up at least partially full of water. Even though the copper Heliax outer is more compatible with water in the long term than most metals I'm not sure I'd want it to be permanently immersed.

Cheers,

GJ

[ms660]

Don't be tempted to use the old black pipe, it can leak.

Lawrence.

[G8BBZ]

Hi Steve,
Heliax is designed to be suitable for direct burial - there is even a version available with an insecticide impregnated outer sheath to protect against termites, though i doubt you will find this variant in the UK.
The outer sheath must be intact when laid - even a pinhole will allow groundwater to seep in over time and start corroding the copper sheath.
Connectors should not be buried, if you need an inline splice the ends should come to the surface and ther splice be located in a box or somesuch.
You will find it difficult to pull LDF4-50 through any kind of pipe over any distance greater than a few metres as the friction between the pipe and the outer sheath will be very great.
Buried feeder would normally be laid in an open trough and the lids put on when the cable install is finished. If trough is not an option, direct burial is probably the best bet, noting previous comments about depth, protection, marking etc. 12" deep is probably a minimum, 18" would be the normal commercial spec.
Good Lick
Peter G8BBZ

[Radio Wrangler]

Direct burial needs to be surrounded in something soft. Small (or large) stones can crush the outer

We ran some surplus gas yellow alkathene piping from our antenna tower down to our clubhouse with heliax fed through it (The secret was th have the tubing straight, the heliax straight and fed it in with a lubricant soap before burying) the open end at the mast collected water in the gas pipe, so we had to add a hole before it got routed into the clubhouse! it worked for the 20 years we had the premises and may still be there.

I didn't want to directly bury the heliax, there were young trees and the ground was waterlogged peat moor.

Some of the club members worked at Andrew Antennas plant nearby, so we benefitted from good advice.

David

[G6Tanuki]

Properly installed, Heliax is waterproof; I've seen it direct-buried in a Scandinavian bog where it survived for the entire decade I was involved. Use the proper [eye-wateringly-expensive] connectors, not some of the 'bodges' that are sometimes promoted in the ham-radio journals.


Please don't go using 'odd bits of inappropriately-coloured pipe' for containment of any buried cables; to me, using yellow or blue pipe to carry electrical/electronic/data services is just as much of as in as using coax to carry 240V (yes I've seen that done...!). The utilities-company that discovers your wrongly-coloured and undocumented duct in 20 years time will not be happy.

And yes, underground ducts need proper protection - backfilling the trench with something like pea-gravel followed by a [suitably coloured] tape before topping-off with soil is SOP, specially in soils which are naturally rich in sharp, damaging flints!

[John KC0G]

I am adding to the two previous comments.

Earlier today I watched a (very good) presentation by Frank, W3LPL, as part of the Contest University 2021 online event. See https://www.contestuniversity.com/ The presentations will be online at some time in the future.

There can be significant ground movement due to frost in the winter (here in Minneapolis, all building footings have to go down at least 42" below grade). His advice when burying heliax in rock soil is to lay it on a bed of sand and then complete cover it with sand before filling the trench.

73 John

[AC/HL]

Our Riggers used Denso tape on all exposed Heliax connectors. Messy, but provides good long term weatherproofing.

[G6Tanuki]

Denso-tape [or its friend Sylglas] are indeed disgustingly-messy - and should honestly be consigned to distant memory given that our friends Raychem inroduced adhesive-lined UV-stable heat-shrink tubing something over 4 decades ago!

[joebog1]

Self amalgamating tape is best for connectors. FRESH self amalgamating tape, not that 1/4 roll you have had rolling around in the toolbox. Heliax can be directly buried, BUT it's better off in conduit. At CSIRO we used 4" PVC water pipe that was cleaned, primed and LIBERALLY glued. As mentioned before, the conduit must be straight, the Heliax must be straight. If corners are necessaryry use slow bends, not the abrupt 90 degree corners. They are slipped on as needed as you will have to "feed" it by hand. It's a PITA job and whatEVER you do, DO NOT BEND the hHeliax tightly. Clean and glue corners as required. At either end of our runs we had a sheet steel box above the termination, that was fitted reasonably tightly to an angle iron frame, that was cemented into the concrete used for the termination box. If security is a concern it's easy enough to fit Abloy locks to two sides of the protection case.

Joe

[eddie_ce]

I always ran underground heliax on a bed of soft sand and covered it with a layer of the same before the yellow tape warning of buried cables. The trench was at least 18" deep, preferably 2'. Never had any problems.

I always used decent connectors covered with self amalgamating tape (Denso is far too messy, I only use it for earthing rods) and protected from UV with a couple of layers of UV resistant electrical tape.

Just my 2 Eurocents worth.