You asked a few questions. First things first. Here's my step-by-step
approach to deciding on what coax to choose:
1. Decide on the loss you can accept in your coax run from TX/AMP to
antenna. I use W3LPL's rule of thumb that says no more then 1 dB of loss
in the transmission line. Then, determine the distance, in cable-feet, of
coax you'll need. Then, find the minimum size coax that will do the job
including taking into account the power level that the cable must handle.
My Website www.erols.com/n3rr (click on Cabling Subsystem) has a chart
provided by W3LPL that will assist you in this.
2. You then need to determine if you want to provide for adding/replacing
any cables once you bury them. If you do, you'll want to use some kind of
rigid conduit, like schedule 40 PVC. Using Schedule 40 PVC will allow you
to pull in cables and pull them out if the overall length is not too long.
For example, I use 3 inch SH 40 PVC for the 60 ft run to one of my towers.
I originally had 3 runs of RG-213 plus a run of 8 conductor rotor cable in
it plus a pull cable of 5/16 inch Daycron rope. About 10 years later, I
pulled out the RG-213 and replaced that with four runs of Andrew LDF-4 (1/2
inch hardline). Using the SH 40 PVC allowed me to do that quite easily with
one person at each end of the conduit.
3. If you do not want to be able to expand/extract your cables, you still
may want to use PVC if your buried cables will be subject to underground
rocks that may contact and harm the cable. In this case, you may want to
use the corrugated PVC which is cheaper than SH 40.
4. If you want to direct bury the cables, then choose a cable with a jacket
that is suitable for direct burial. RG-213, certain RG-8 cables and RG-8X
also have direct burial jackets. Be sure to check with the manufacturer. I
buy all my cables from RF Connection (link on my site - "Vendors") and they
will tell you about the attributes of each cable before you buy it.
5. As far as depth of burial, it should be below the frost line (18 inches
is the recommended depth in Maryland).
6. There are a few other considerations including: connectors, grounding,
lightning protection, building penetration and the like that also must be
considered when deciding on cables as well.
Disclaimer: I have no interest in RF Connection or any cable/conduit vendor.
----- Original Message -----
From: Michael Wacker <firstname.lastname@example.org>
Sent: Saturday, April 28, 2001 2:09 AM
Subject: [TowerTalk] Coax
> What coax should I use for running it underground? How deep? Should it
> be enclosed in PVC pipe or similar? Any help would be appreciated.
> Mike N3HR
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