[TowerTalk] ground rods for towers

[Bob Wanderer]

This system was used by the Las Vegas (Nevada) Metropolitan
Police Dept to protect their repeaters up on the 7000'
mountains surrounding the city.  It is described in the
"grounds" book too.  Since the installation, the police have
never lost any gear to lightning-induced surges.

I would suggest as many radials as possible, rather than
limiting it to four, and using as wide a strap as possible.
Going past 50~75 feet (per radial) is, as Joe mentions,
unnecessary.  You can also use rocks and whatever to cover
the radials so no one trips on them.  This will also help
the efficiency of the system as the way it promarily works
is that the high E field on the edges "arc and spark" over
to the ground and rocks.

If you have "some" topsoil, you may want to consider using
coke breeze or other enhancing material.  Coke breeze is the
remains of using coke for electricuty generating devices.  I
am aware of one source in Utah, but I am sure there are
others.  PolyPhaser may have that information.

Good luck.

73
Bob AA0CY
former PolyPhaser Technical Consultant

-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Joe
Reisert
Sent: Monday, July 31, 2000 4:24 PM
To: Adam at Home; towertalk@contesting.com
Subject: RE: [TowerTalk] ground rods for towers



Adam,

A few years ago I discussed this same problem of rocky soil
and rocks with
Roger Block, former owner of Polyphaser. My land mostly
consists of a thin
layer of soil on top of rock (NH is the Granite State!) and
I can't drive a
stake even 2 feet down!

So, for this type of soil, Roger did some tests and
recommends that you use
1-1/2" wide thin (.015" thick) copper strapping. The best
plan is four (4)
straps 50 feet long 90 degrees apart. Above 50 feet has
diminishing results.

Polyphaser sells this recommended copper same strap.
However, I bought mine
from Metal and Cable in Twinsburg, OH (who was less
expensive) for about
$25-30 for each 50 foot strap. Pretty cheap protection and
it also becomes
part of my grounding system for shunt feeding the tower on
160 meters.

Furthermore, all you have to do is lay the copper straps
right on the
ground! I bolted my four (4) copper straps to a brass plate
that is in turn
strapped to the base of the tower with a piece of the same
copper strap. It
probably would be OK to just attach each strap directly to a
tower leg with
a few hose clamps.

73,

Joe, W1JR

At 08:28 AM 7/31/00 -0500, Adam Adkins wrote:



> > -----Original Message-----
> > From: owner-towertalk@contesting.com
> > [mailto:owner-towertalk@contesting.com]On Behalf Of
K7LXC@aol.com
> > Sent: Monday, July 31, 2000 8:11 AM
> > To: w4th@webtv.net; towertalk@contesting.com
> > Subject: Re: [TowerTalk] ground rods for towers
> >
> >
> >
> > In a message dated 07/31/2000 12:09:51 AM Pacific
Daylight Time,
> > w4th@webtv.net writes:
> >
> > > How many ground rods should be used on a tower of 75
feet? This tower is
> > >  used only for beams and dipole support. I have a
friend who says one is
> > >  enough, I have others who say one on each leg, what
say ye me hearties?
> >
> >     Since you're in a spot that gets a significant
amount of
> > lightning, I'd
> > be sure to do a decent job. Three ground rods per leg
spaced a rod-length
> > apart is a good start.
>
>         I assume you are talking about 8' ground rods.
Here's a question
> regarding
>about getting adequate protection from those ground rods
when you live in an
>area that has very rocky soil.
>
>         Actually, although the soil is very rocky, that
isn't the major
> problem.
>The biggest concern is the solid rock that is about 24"
down from grade.  It
>is impossible to drive a ground rod vertically into that
rock.  Can I borrow
>a trick from the electrician's trade and bury the rods
horizontally in
>trenches to get the same kind of lightning protection?  And
if so, how far
>apart should they be spaced?
>
>         Thanks!
>
>73,
>
>Adam Adkins, KM5N
>
>
>--
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