Glenn Maclean wrote:
(much snipped by Dave)
This leads me to my question. Is anyone out there using a Ufer ground
as a counterpoise or to ground their tower and station?
I have been for the last 12 years or so; I highly recommend them. In my
installation, it approximates a commercial station I toured prior to
starting construction. Some notes:
1. in setting all the rebar for the foundation, as it was tied, and
before the concrete was poured, all the points at which the rebars
touched each other were cad welded (I think this is the term but
it has been a while); the process uses little molds that are
filled and then fired, resulting in a corrosion free weld (no
oxide in between) huge "cage" that is in the concrete, similar to
your normal rebar structure as far as structural strength, but,
electrically bonded. This is apparently capacitively coupled to
ground (fairly low inductance as well).
2. the advantage for lightning strikes seems to be that the whole
ground system floats and then drops back down, so there is little
differential (ground loop currents) so most stuff in the house is
better protected.
3. My tower (its base is part of the Ufer ground) has an excellent
counterpoise from it; I have 70' tower, with a 8 element LP for 20
- 17 - 15 - 12 - 10, and a 6 el. Yagi on 6 M.; a full wave loop
on 60 M, and an inverted L on 80 and 40, and a 160 - 10 M. B&W
wide band dipole set for NVIS. They all appreciate the better
ground it offers.
4. the cable entry to the shack (feed lines, coax switch, rotor
control, etc.) all come in at a common entry point with all
shields grounded prior to entering the shack, common ground, etc.
5. I have taken several direct strikes (on top of a hill; all the
trees in my yard have evidence of having been hit sometime); the
first one was sufficiently strong that it took out a cable TV
distribution amp 50 yards away that was buried - it took out the
AC compressors, (lightning jumped to them as a supplemental path
to ground?), the telephones, and the burglar alarm, but almost
everything else in the house survived it by floating with the
changing ground. It even blew a chunk of concrete out of the
tower base, where the rebar was too close to the outside of the
concrete, and some water had gotten in, becoming superheated
steam. That chunk weighed over 20 lbs, and it went over 50 yards
away (unhappy neighbors).
I am convinced (and more importantly, so is the xyl) that without
it, the house would have burned for sure.
We are building another home, but it is in an area with the dreaded C&R
stuff, so no tower; we chose not to do Ufer grounds there, but I wish I
had; I now figure I will have to run a ground wire under the long wire
antenna to help it out...
(and, yes, the search is on for about 10 acres so I can get a
competitive 160 and 80 meter array with a good ground going.)
This seems way better than the old ground rod pounded in the dirt.
Definitely way more expensive too, but seriously better in terms of both
an RF ground, and lightning protection.
Any comments would be appreciated.
Glenn WA7SPY
Sacramento, CA
73 de W5SV, Dave
--
David F. Reed - W5SV - cell: 512 585-1057
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