My thoughts on a ground system.
When you go through the calculations, my current preference is based
partly on these regs, calculations and experience.
"I believe" a tower of any type should be planted enough concrete(don't
go overboard) to serve at least, a small UFER ground with some sort of
network resembling a star. All this in conjunction with a single point
ground (SPG) . Often, construction does not allow a true SPG in many
homes. Wiring lengths and route in the house can make a true SPG,
impossible. Rare is the house where the station leads, cable, phone,
electrical, TV/satellite can form a true SPG. And where it does, are all
leads from the SPG to the equipment, the same length?
It's not just the SPG, but a well designed electrical system that allows
for the station to use a SPG for the most benefit.
I have, Phone, Cable (Internet), fax, CAT5 network, and servers. Cable,
electrical, and hard wired telephone come in through the front, while
every thing else comes in through the back. The only problem has been
that CAT5 network, but that has been solved. with high speed wireless
and parabolic reflectors to keep the receive angle narrow while the
power between the den and shop is high allowing for near gigabit
wireless. Only one computer remains in the shop with no network storage
out there.
For most hams, the cost of a real, efficient ground system is not
realistic, from a cost, and / or area standpoint, so we do the best we can.
Follow good practices and put as much as you can afford into a good
safety ground.
Were I to do it over, when I was working and not living on a pension and
SS, I'd put up a heavy duty, 120' crank up in place of the 100' 45G plus
a 70 or 80 footer by the back of the shop.
I have a rather elaborate safety, ground system in a more or less star
with over 600 feet of bare #2 and 32, or 33 fround rods that cover a
wide area of our one acre lot. That was when Copper was a fraction of
today's prices ans steel was abt 1/4 to 1/3rd of today's prices.
Remember: No practical ground system provides 100% protection
The US Military uses huge UFER grounds for bunkers in desert
conditions. I havent heard of any complaints.
73
Roger (K8RI)
On 1/10/2016 Sunday 3:48 PM, jimlux wrote:
On 1/10/16 11:40 AM, David Robbins wrote:
At lightning current densities and time scales the earth ionizes and
rapidly
increases its conductivity. See equations by Weck and others:
http://www.ipstconf.org/papers/Proc_IPST2011/11IPST109.pdf
Note in the graphs how the effective resistance of the ground
decreases as
the current increases.
Very interesting..
(and, of course, there's about a 3:1 difference among the various
models, which I'd sort of expect)
That paper and the references it cites will give me a fair amount of
reading.
However, I don't see any sort of "saturation" behavior: in fact, it's
more of a negative resistance (i.e. resistance goes down as current
goes up).
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
jimlux
Sent: Sunday, January 10, 2016 17:42
To: towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: [Bulk] Re: copper or galvanized
ground
rods in red SC clay
On 1/10/16 8:56 AM, Roger D Johnson wrote:
Another factor not usually considered by hams is that conduction
through the ground is NOT the same as conduction through a copper
wire! A copper wire has a copious supply of free electrons and will
happily conduct increasing amounts of current until it melts. In soil,
the conduction is by ions from metallic salts in the earth. The supply
of ions is finite and when all are being used to conduct electric
charges, the resistance rises sharply. The soil has gone into
"saturation".
do you have a reference for this? I'm interested in a more technical
description of the phenomenon.
I'm familiar with some other soil and tissue conductivity phenomena
relevant
to RF having to do with the ion mobility (e.g. the Cole-Cole model
which is
used for all sorts of things at all sorts of frequencies:
prospecting for ore, measuring the ripeness of produce, and RF
imagery of
human bodies)
A lightning ground system
has to be designed to dump the current from a strike into a large
"volume" of earth capable of conducting the strike current.
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73
Roger (K8RI)
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