There are a couple of points to ponder with underground coax insatallations.
1. Protect the coax jacket from damage. Try running the cable inside
a PVC pipe to prevent physical damage.
2. Consider trying to keep water from collecting around the coax cable.
Water will only shorten the life span of the cable. Any pin hole openings
in the jacket will allow any moisture inside the cable and destroy it
over time. Don't make the PVC run level. Put a good bed of stone
and sand at the low point to drain away any water.
3. Protection from lightning will be enhanced by going underground with
the coax cables. Only problem is make sure your not placing it near
any underground utility lines that may conduct electrical current. The
lightning has a tendancey to jump from one conductor to another in
an underground installation. Don't just bury the PVC just under the
surface. Go down at least 6 to 12 inches. The National electrical
codes use 18 to 30 inches as the depth for electrical services. This is
not an electrical service, so you don't fall under that guide.
4. What some of the telephone and cellular companies do is run all their
underground cable feeds into their shelters by running the cables
through about a 6 foot section of steel conduit. They tie this conduit
into their ground system. It acts like an RF choke and reduces any
induced voltages from lightning.
5. Don't forget to ground the tower and install grounding kits on the
coax cables. This tower ground should also be the same ground as
the ground used for the building equipment ground. Install another
ground kit on the coax cables where they come out of the ground
and go into the building. Most ground systems use # 2 AWG solid
copper wire that is tinned to reduce corrosion. They install ground
rods at 16 foot spacing along the run of the ground wire. All the
connections made to the ground wire are done with exothermic
welds. This provides the strongest connection and the lowest
resistance. The connection also doesn't change over time.
This may sound like allot of work and effort, but you asked and here are
the facts. Been doing radio installs for about 35 years and in the cellular
insatlls for about 14 years of that time. If anyone tells you that you can't
survive a direct hit on the tower, tell them they don't know what their
talking about.
Many comercial sites take hits all over the country on a daily basis.
They stay up and operating. Look at your local TV towers. You can
be watching the station during a storm and the tower takes a hit.
It might cause you to see the picture change color or go away for an
instant. But it comes back and continues.
Jim
kb5udf said:
I am unaware of any technical reasons why running coax underground would affect loss (assuming intact coax w/proper shielding).
