> I have 3 towers up, one at 80', one at 50' and one at 70'.
Each is a Universal Aluminum self supporting tower which I
have supplemented with a single set of 3/16" steel guy wires
about 2/3 of the way up. Each tower leg has it's own 10'
ground rod connected with a 3' length of #0 wire. >>
Unfortunately you have almost no ground at all on the
towers.
>The towers are each separated by 130' and are in a straight
line configuration. The 80' tower has a short 40m rotatable
dipole at 90'. At the 80' level I have suspended an
inverted vee for 75m. Each of these was fed with not quite
300' of 9913F type coax. The cables were currently lying on
top of the grass as I had just installed them 2 weeks
earlier. I was just starting to play on HF after many years
on VHF SSB and MS. The 70' tower has a new X7 at 75' and
the 50' tower has a pair of 17B2 on Az/El for moonbounce.
>
.....and a good path back to the shack through the cables.
> All rotor cables and coax from all towers terminate to a
18"x18"x1/8" Aluminum panel I have in place of one of my
basement windows. The panel is at around ground level and
uses N-type feedthrus. The panel has 2 mechanical
connections for ground. Each one has attached a 3'-4'
length of #6 wire that goes to 2 10' long, 3/4" copper
pipes. The panel thus has 4 ground rods. When I am not
using the shack all cables and coax are physically
disconnected from the panel (from the inside) and separated
from the panel by a foot or so. For almost 10 years this
setup has seemed to serve me well and I recall riding out
some terrible storms with tons of hits all around the QTH
with no misfortune. All equipment was connected to AC power
but not turned on.>>
...and a bit better ground back at the entrance.
> This has taught me that my towers are not very well
grounded nor is my entrance panel. It also has shown me
that anything located near the panel is vulnerable to flash
over.>
You not only had a very poor tower ground, it sounds like
the entrance panel was never bonded to the power mains
entrance ground! If we don't bond the entrance panel to the
utility ground it is a big problem (and goes against the
national electric code).
As you painfully found out, ground rods do next to nothing
for establishing a good ground. A poorly grounded radio
entrance panel that isn't bonded to the utility entrance is
also a big problem.
It's pretty easy to see what happened. With virtually no
grounding on the towers the lightning needed an earth
connection. With multiple cables routed above earth level,
there was a very good direct path to a collection point that
was marginally grounded. Near that marginally grounded
charge collection point you placed a path with some small
air gaps (small compared to the distance from cloud to
ground) to the radios that were grounded to the power mains.
The radios provided a ground path back through your house
wiring to the power line entrance panel, where all those
miles of wire and grounds on poles provided the only
reasonable ground in the system.
My system is a bit different. I have towers ranging from 160
to 318 feet tall. Each tower has a few short ground rods,
they mainly serve as a place to attach a ground buss that
circles the base of each tower. The ground buss on each
tower has at least 50 buried radials that are long and
straight. (None of the tower grounds are connected because
they are too far apart for an effective connection) . My
feedlines and control lines are all underground for some
distance (at least 200 feet) before reaching the house and
my workshop.
My entrance panels are bonded with 3 to 4 inch wide copper
flashing to the service entrance panel, and to a buried soft
copper tubing that circles the house. That buried copper
tubing circling the house a few feet away from the house
bonds to the TV tower, the Satellite Dish cable, the telco
and power mains grounds, the copper water pipe feed from
the pump house, and so on. Every conductor entering or
leaving the house bonds to that copper tube ground buss.
My radio room has an internal panel at the entrance point
for my desk, and every cable coming from the entrance panel
goes to that panel. At that point on my desk the power lines
and the antenna cables are common grounded.
My 300 ft tower takes several direct hits a year. Damage is
minimal and confined to cables around the tower base. It had
one hit over the past few years that partially melted the
copper flashing and melted the shield on my 7/8th inch
heliax, but other than magnetizing CRT's in the TV sets
nothing in the house was damaged (other than a few 1N4001
diode clamps on LV control lines).
Here's the interesting part. I don't disconnect my rigs!
Everything stays connected. I don't have any lightning
suppression devices on control cables or on feedlines other
than a few diodes on LV control lines and MOV's on power
lines and telco lines. I suppose it would be better to have
something at the entrance on cables, but I don't bother. I'm
still doing things like I did with broadcast stations and
repeaters in the 70's. Since virtually all of my installs
would run through lightning storms (you couldn't buy any of
the lightning protection devices available today back then)
I still do things that way.
99% of damage control relates to how things are routed,
bonded, and grounded.
73 Tom
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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