Topband: Ground Screen Question
jim at audiosystemsgroup.com
Mon Jan 11 13:38:52 EST 2016
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
On Mon,1/11/2016 6:47 AM, k3ky at radioprism.com wrote:
> Hi, Bob-
> I wouldn't risk this, personally, for the small benefit that might be
> gained. Consider- if your tower ever takes a direct lightning hit,
> nearby ground currents can be very high indeed. There are some cases
> documented where concrete fractured or even exploded as a result of
> these violent internal currents. Even many decades old, it still has
> some internal moisture content. During the pulse, it flashes to steam.
> That energy has to go somewhere. The same thing happens when lightning
> shatters a tree- due to the high current density, the internal sap
> flashes to steam and the tree literally explodes. If I were looking
> at this problem, I'd be asking myself "how can I encourage the pulse
> of current to spread out alongside and parallel to the driveway?"
> Our neighbors took a direct hit to their roof a few decades back-
> some recently planted shrubs next to the underground transformer in
> their front yard literally exploded out of the ground and landed some
> 15+ feet away in the street out front. I would never underestimate
> the potential for mayhem when it comes to lightning.
> 73, David K3KY
> I searched the archives under "ground screen" and could not find info on
> my situation.
> I have a 15 foot by 70 foot, 6 inch thick concrete parking slab along
> side our house. My tower
> is about 15 feet away from the side of the slab. I am planning radials
> to extend out from the tower which
> I will be shunt feeding for 160M and remembered that the slab has
> welded wire mesh reinforcement
> at mid depth. The welded mesh is 6 in by 6 in and # 8 wire. Would the
> mesh be a good ground screen ?
> I will have to drill and connect to the mesh at various places but would
> be worth it if a good ground screen.
> Topband Reflector Archives - http://www.contesting.com/_topband
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