Conrad,
Not sure what you have locally, probably something similar in metric or
still Imperial in the construction trades -
IMO, regular sch40 PVC conduit is the best choice for moisture, critter
and crush resistance. Use 3" or 4" diameter and the large radius (min
36" radius) sweeps (90 degree bends). 3" will hold 3 x LDF5 plus
control wires if pulled together with liberal amounts of pulling lube.
I recently recovered a dozen runs of LDF5 from several 3" x 140'
conduits and it removed easily as the condensation inside the buried
conduit kept the 8 year old lube slippery. For both ends, buy a large
fiberglass enclosure (24 x 36 x 12" or larger) and put your grounding
plate in it with RG jumpers into the shack from there. Or use 90 degree
connectors if LDF has to go into the shack for some reason. The station
I recently took apart was all 7/16 DINs to a 2' x 3' Cu shack end ground
plate with 20 bulkhead through F-F DINs soldered to it - very first
class! I mounted my enclosures so the tower run conduits enter at the
bottom and the two through wall 3" conduits for RG jumpers into the
shack go out the back. For 4 towers you will probably need more than
one enclosure at the shack end. Similarly at the tower end the
enclosure with the bottom of the tower grounding plate holds the
lightning arrestors and transitions to the coax runs up the tower,
whatever they are. The tower runs go through holes in the cabinet
bottom so there a drip loop. The cabinet is also a good place for
stack switches.
Glue all the conduit together and bury it before pulling wires. If the
soil has sharp rocks, some "5/8" and down" gravel bedding and cover will
protect the PVC from being punctured. Sand is often the code standard,
but it washes out easily if there is an opportunity for that. Conduit
measuring tape is a good way to run a messenger line, tied to a crumpled
up plastic bag and sucked through with a shop vac. Then you will know
the exact length for the LDF. I've been surprised when the calculated
length was shorter than the measured length and cables were cut - oops!
Run extra cables for the future (mine are CAT5, RG6, 8 wire 18ga
control, 1x Buryflex RG8), since as others have pointed out, it's very
difficult to pull a new cable in conduit with existing cables, but leave
a couple of measuring tape lines "just in case". A 3000' spool of
measuring tape costs about $80. btw, use braided rope or the flat
webbing made for wire pulling as the pull rope, not 3 strand rope since
it will cause twist in the cables.
It takes a pressurized dry air or nitrogen system to keep condensation
out of buried conduit, so plan to use control and power wires rated for
burial. Some are flooded with silicone grease to prevent moisture
wicking if the cover is nicked.
Grant KZ1W
On 3/4/2014 9:34 AM, Conrad Farlow wrote:
My radio club will shortly have 4 towers and I would like to run
lengths of LDF5-50A to the base of the tower from the shack. The
lengths are not particularly long but I would like to bury them to
keep them neat. I have very little idea of how to do this properly, in
particular how to put a correct bend into the cable where it leaves
the ground pipe and enters the shack. Does anyone have any photos'
guidance on how they have done this?
I am assuming that the cable should be put inside some large diameter
plastic pipe that has a good number of pull ropes installed prior to
burying them.
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