RadioBanter - Base Antenna Mounting

"Keith Hosman" wrote in
message ...
On Sun, 15 Feb 2004 19:33:27 -0800, Frank Gilliland
wrote:

Ok......

First, sink a ground rod at the point where the coax will enter the
house. If
you have a basement next to the ground rod, sink a couple more rods so
they are
separated by ten feet or more and in the path of the coax. Some people
like to
prep the ground by soaking with sal****er, but in my experience that
makes the
rod corrode before its time, then the salt leeches away into the ground
water,
leaving a very poor ground in a very short time. I use galvanized pipe as
opposed to copper rods because they have a larger diameter (more
rod-to-ground
contact = lower resistance), and they last longer. You can also thread
the pipe
for a super-neat installation of a waterproof box......

Next is the coax installation. Run the coax down the mast or side of the
house
to the ground rod. Don't run the coax near any wiring inside the house.
You can
detect house wiring with a cheap metal detector. Avoid sharp turns as
much as
possible. At the ground rod it helps to have a waterproof box because you
need
to cut the coax, ground the shield, and shunt the center conductor to
ground
with a choke (as per the diagram I made yesterday).

About the choke: This serves two purposes. First, it shunts static
electricity
from the antenna to ground. Second, it provides a path for lightning if
it
should strike. Since the lightning will arc across every loop in the
choke, the
inductance value isn't critical just as long as it is high enough to
block your
RF (about 1 mH or larger for HF and above), and the wire size is large
enough to
handle some current (#14 or larger should be fine). One of those
heavy-duty hash
chokes for ignition noise is ok, or you can wind your own -- use a large
iron
bolt for a core and wind about 50 turns of #10 or #12 house wire. If you
aren't
running much power, you can slit the insulation along the length of the
coil so
it will arc at a lower voltage.

Then run the coax up into the house along side the grounding strap. Tie
them
together with cable-ties if you want. Again, it's important that you run
these
so they don't come close to any house wiring, and they should enter at a
location that is clear of easily combustible stuff. Terminate the ground
strap
with a really big alligator clip, jumper cable clamp, or whatever you
have that
makes a really good connection and can be easily disconnected. The ground
clamp
from an arc welder is almost ideal.

Above the point where the coax and grounding strap enter the house, make
a hook
or post where you can hang both when not being used. Remember that if
lightning
hits, it's very possible that these will jump straight out from the wall
and
dance around like a water hose, so make sure they are held securely in
place.

Inside the house, make yourself a grounding bus bar of copper or
aluminum. Put
this on the back of your bench and use it to ground all your equipment.
To this
you clamp on your grounding strap. When not using your bench, unhook the
grounding strap along with the coax and stow it away. Also, to protect
the coax,
use an appropriate socket and short it out before you stow it.

When should you unhook your antenna? There is a thing called the 30-30
rule: If
you hear thunder less than 30 seconds after you see the lightning,
unplug. Don't
plug in again until 30 minutes after the last thunder. That's pretty
safe. You
can even improve on that by building a lightning detector, many of which
will
indicate lightning even before you can hear the thunder.

How's that?

Oh, I almost forgot..... coax length!!!!! The low impedance of the ground
will
be reflected at the radio when the length of the coax & ground strap,
from the
ground rod to the radio, are 1/2 wavelength. This means 1/2
wavelength -without-
consideration of velocity factor because we want a low
impedance -ground-. And
this means -- you guessed it -- 18 feet of coax!

My previous dwelling besides having a similar setup to what Frank
described I also had my antenna and tower grounded. I put my tower out
in the old garden bed (I moved my garden every few years so as to give
nutrients a chance to rebuild), and before I put fill dirt and grass
seed in I laid out a grid of #12 copper wire in a 18' radius from the
tower legs, this as well as the tower and antenna were tied into a
ground rod at the base of the tower. I had a weatherproof box outside
where I could disconnect coax so it couldn't feed into house during
t-storm.

I'll be setting similar situation up here at the new place, this time
for my HF Vertical, my UHF/VHF antennas, and my multi-band Inverted V.

73 de Keith
--
KC8TCQ
ARRL Member - ARES
SKYWARN

Don't forget to ground your tomato plants. g