Topband: RE; Ground screen Question
k6uj at pacbell.net
Tue Jan 12 15:37:15 EST 2016
I see your point. I wouldn't want to chance damaging the concrete.
I am not thinking of attaching to the tower with it however, I am
thinking of it
as a ground screen and actually adding more welded wire mesh also at
about a 15 foot radius
around the base of the tower which would be connected to the slab mesh.
The ground screen would not be
attached to the tower and will help with near field losses from the
shunt feed tower. What I am thinking of
for radials is 4 elevated radials at 14 to 16 foot above ground. This
height works well with my trees, etc on
the property. Radials will not connected and completely independent of
the ground screen. I don't have a huge lot so the radials will have to
be bent at 90 degrees when they approach the property lines. Not ideal
but I'm hoping with a little help from the ground screen I will have a
decent signal. I did an exploratory hole
in the concrete slab and the 6x6x no 8 wire grid is like new, no rust.
I guess the concrete preserves it.
I have two 8 foot wide by 70 foot long runs of the welded wire mesh
imbedded in the parking slab. I will make
sure each of the two runs is electrically tied together. So what I will
end up with my proposed ground screen is wire mesh ground screen
extending out from the base of the tower with a 15 foot radius and it
will attach to the adjacent 15 foot by 70 slab ground screen. I figure
why not use the 15 x 70 slab too if doable ? Sound OK ? Any other ideas
suggestions ? I appreciate the input guys !
On 1/12/16 11:29 AM, k3ky at radioprism.com wrote:
> No confusion at all, Jim. I know the difference between the two.
> His reinforcing steel inside his driveway is probably way far
> out of the realm of Ufer grounds, due to it being small gage
> conductors. Aside from the great difficulty of boring into theDave
> this anyway out of concern that the current density during a
> major lightning hit might be sufficient to produce widespread
> cracking of the concrete.
> Now I'll have to go re-read and brush up on Ufer grounds, but
> as I remember, his driveway setup would be woefully inadequate
> for the possible current levels involved in the event of a direct
> lightning strike. Personally, I wouldn't go there. A concrete
> drive would be a little pricey to replace, especially considering
> the relatively small prospective gain in HF ground quality he
> might see by connecting his radial field to it. I'd much rather
> connect *over* that drive using strategically sawed grooves
> and lightly concreting in a few wires at the surface in a few
> places- this assuming he has somewhere to go on the far side of
> the drive with those wires anyway.
> I know a ham who thought his well pipe might make a dandy
> addition to his ground radial system. He connected it, and
> eventually had to replace a 600 dollar well pump after a strong
> lightning hit on his property. This driveway question reminds me
> of that. Properly designed Ufer grounds, fine- but I sure don't
> want to invite lightning hits to dissipate through anything
> concrete on my property. My two cents (two dollars, adjusted
> for inflation...)
> David K3KY
> There is considerable confusion here with respect to radial systems for
> antennas and an earth connection for lightning protection. They are VERY
> different, and both are important. Properly bonded conductors buried in
> concrete ARE acceptable as a ground for lightning protection -- it's
> called a Ufer ground, after Herbert Ufer who developed the concept, and
> it's now recognized in the National Electric Code. A Ufer ground works
> because 1) concrete is conductive and 2) there is a large surface area
> in contact with the earth. The downside is that the earth it makes
> contact with is near the surface.
> Like ALL earth electrodes, it must be bonded to all other grounds in
> your home -- power system, Telco, CATV, your shack, and all driven rods.
> I think Bob is on a pretty good track with his design.
> For more ideas, see http://k9yc.com/160MPacificon.pdf
> 73, Jim K9YC
> Topband Reflector Archives - http://www.contesting.com/_topband
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