>"My thoughts, so far, are to start from the highest point, with: 1. A
mast with rotator, bonded to the tower, with the topmost antenna
down, say, 5ft from the mast top so the mast forms a sorta lightning rod"
I think that's mostly a "feel good" exercise. Focus on the bonding effort.
OTOH, I have a DC grounded M2 3 el. 30m monobander at 115 ft. above a
4-element SteppIR at 100 ft. My own "feel good" thought was that the 30m M2
*may* offer some protection to the SteppIR. I doubt it, but it felt good.
>"2. Cable shields tower-bonded top and bottom"
Yes. Use coaxial cables that can be fitted with commercial grounding kits.
Bond at the top and bottom of the tower(s). Create a ground field with many
rods around each tower. I have ground kits installed on LMR600.
>"3. All cables in a trench to the single point bunker entry"
A master ground bus (MGB) is an absolute must-have item. Install a copper
bulkhead (e.g., from Georgia Copper) just outside the shelter entry.
Install another on the inside wall, opposite the outside MGB and pass the 6
inch strap through. Keep the MGB low and near the ground. Drive a ground
rod deep below the MGB and bond to it. I have a 24 ft. rod below the MGB.
Use 6-inch copper strap from the MGB to a ground bus bar inside the comm
shelter. Bond every I/O cable at the MGB. That means all coax and control
cables. Consider using Polyphaser devices at the MGB for each line. The GA
Copper bus bar allows for drop-in Polyphasers.
For rotator and SteppIR control I'm using multi-pole arrestors at the MGB
and at strategic points on the tower. I suggest using hardline or LMR600
from the towers to the MGB, then use any RG-213 variant from the MGB to the
inside.
You must bond your AC entry panel to the MGB. Try and create a ring ground
around the building perimeter if not already present from the prior use.
Use a lot of ground rods and Cadweld them or use 15% silver-solder with an
oxy-acetylene torch. No soft solder. I'm using 50 rods in total, four of
which are 24 ft. in length due to poor soil issues. Depending on distance
from the comm shelter to the towers, consider bonding each tower with a run
to the MGB in a trench. In between, drive down more rods. However, there's
a practical distance limit to a dedicated tower bond due to increasing
inductance as a function of distance. K9YC has some info on this.
>"I'm stuck here: How can I best protect the sensitive data and rx/tx ports
on the gear, which will be set up on a grounded metal operating table,
inside the bunker?"
Run a copper strap from the inside ground bus bar along the back of the
operating table. Tie to that strap, keeping connections short. You can
then use data line suppressors that are bonded to the strap.
I'm not inventing anything new in my suggestions. It's all from Motorola
R56, available as a download from my QRZ page. I don't disconnect anything
no matter how bad the weather. Neither do cell companies, although I get
that they have bigger budgets and are essentially self-insured in the event
of loss. Still they cannot afford down time. Follow R56. My site is up
24/7 with no disconnects. Towers are 140 ft and 100 ft. in height.
Paul, W9AC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|