[TowerTalk] Installing/burying LDF5-50A

[Kevin Kidd]

Conrad,

After having installed thousands of buried feet of LDF type products for
broadcast stations, I can tell you that it is not _extremely_ fragile.
Somewhat fragile yes and care must be taken but it doesn't require silk
gloves.

I don't know what you consider "not particularly long" but for for us
building MW arrays for AM, we sometimes have buried runs of over 1500ft.

Minimum bending radius for most corrigated cable is about 10 times the
diameter of the cable.  There are a series of spec sheets at:

http://www.repeater-builder.com/andrew/

We typically direct bury most cable but I highly recommend installing a
conduit in addition to the direct buried cable for future needs. We
typically use fiber duct.  Short end pieces of fiber duct can sometimes be
acquired for cleaning off the reels at cable contractors.

Depending on the number of cables going in the ground, we typically use a
common trencher and trench to some depth below the local frost line if
possible.  If there are a number of cables going in, we use a
mini-excavator (a lot more fun than a trencher) with the appropriate sized
bucket.  We have also used directional boring at a number of sites.  Prices
for directional boring vary dramatically depending on the location and if
the payment is due on the owners boat.

 If the soil is at all rocky, I highly recommend bedding sand (about 6in
above and below) around the coax in the trench.  This protects the cable
from sharp rocks.  A cable duct is highly recommended for directional
boring.

Also from experience, trying to put several pull ropes in one large conduit
will be an exercise in futility when you try to pull the second or third
cable.  The pull ropes tend to wrap around the other cables and each other
as you pull them through.  This will result in much yowling and gnashing of
teeth on your part as the new cable becomes irretrievably stuck in the
conduit.  I have actually had better luck running a fish tape thru after
the other cables are installed.

You will be much better off to put 2 or 3 smaller conduits with a single or
maybe 2 pull ropes in each.

We typically use either plastic flex or PVC conduit for the transition from
below to above grade for protection from vandals, mowers and weed eaters.
The conduit should extend below grade to some point below the local freeze
line and up to a wall or cabinet OR at least 12 inches above ground level.

Hope this helps,

Kevin C. Kidd, CSRE/AMD
AM Ground Systems Company  -  WD4RAT
kkidd at kkbc.com  --  866-22-RADIO -- 866-227-2346
www.amgroundsystems.com


On Tue, Mar 4, 2014 at 11:34 AM, Conrad Farlow <conrad at g0ruz.com> 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
>