Hi, Dave:
> [RFI] Ground rod placement???
>
To: <rfi@contesting.com>
> Date: Tue, 28 Apr 1998 21:20:47 -0400
> From: "David E. Shelton" <w4des@bellsouth.net>
> Subject: [RFI] Ground rod placement???
>
> Hello all,
>
> I am seriously considering placing a ground rod through my basement
> floor, concrete slab.
That may be a serious error in your part of the world. Holes in basement
floors are notorious springs in wet season and may not provide a better
ground than the rod outside the window [although a shorter run would
help!]
The problem of low-impedance ground point near a rig is often hard to
overcome
due to soil resistivity and your basement floor rod may not be any
better than
the one outside without special help.
One embassy I worked in had a water table that was about 5' above the
basement
floor in the rainy season. The pumps ran full time to keep it semi-dry.
You don't
want that to happen to a marriage!
> I have my shack in the basement near one of the basement windows. I
> previously had the rig and other equipment grounded
> to the 8ft. ground rod immediately outside the window by the shack with
> about a 9-10ft run of ground strap.
Anything less than 4" wide isn't necessarily a ground strap. Common
practice is
to use 8-12" for HF and MW stations.
> However, I have a deep basement and consequently the ground rod was vertical
> to the station and just outside
> on the otherside of the concrete wall.
Not a factor unless it is a poor RF ground.
> With a field strength meter I determined the ground strap and rod were both
> radiating RF.
Strap, yes. Rod, no. A FSM won't tell you what's happening there.
> Now my antennas are on my 50ft tower at the end of the house and the tower has
> three ground rods at its base, connecting to the legs and the lightning
> arrestors, at the base and top of the tower. The previous problem with
> the ground rod out the basement window seemed to be related to a ground
> loop situation.
More likely a ground proximity problem. The rig was acting like a sig
gen
xmtng into a "balanced" line; one side was the antenna, the other side
was the
ground strap!
> I ask all this because I get complaints now when running >60 watts
> output from some neighbors and one day I would like to run an amplifier
> with about 500 watts or so. I understand that the RFI is coming from the
> antennas, Force 12 C4 and home brew wire antennas off the tower, and not
> the rig in the basement but I want the station to be as RF clean as
> possible. So I know I will need a ground rod at the rig/amplifier which
> I do not have now. After the problems with the ground rod outside the
> basement window my elmer suggested to run the station without the ground
> rod at the rig and use the braid of the coax, that is my feedline as my
> only ground which is grounded at the base of the tower approx 45ft down
> the feedline.
>From a lightning safety standpoint, that is nearly the worst solution
imaginable!
> So I am considering drilling a hole in the basement floor
> to drive in a ground rod which would be only a couple feet run of ground
> braid to the rig and all other equipment connected to it.
Again, the driven ground rod is not necessarily RF ground or even good
ohmic ground. Soil is variable and the gods are fickle!
Suggestion:
1) Purchase 3-4 inch wide copper strap and silver solder one end to
outside
ground rod, other to buss bar at your operating position. Connect all
station grounds to the buss bar [which should be brass or copper and
1/4"
x 2" or so.]
2) Drill a suitable hole about 8" from the ground rod and set a 4' long
piece of
4" OD perforated drain pipe in the hole with top flush with the ground.
Fill
the pipe with epsom salts, add one gallon of water and fit a cap over
the pipe.
Renew the epsom salts at 1-2 year intervals. [This is often called a
"made ground"]
3) Consider adding additional rods in a 36" diameter circle around the
epsom salts
"dispenser." Bond them together with 2-4" copper strap.
4) Remember to use copper-plated steel rods and figure on replacing them
at 5 year
intervals.
5) Someone is running a series on lightning protection and grounding
practices in
a magazine I get, either 73 or QST. Get it and pay attention! If you
need it and
can't find it I'll hget the proper reference for you.
6) Clean and solder all wire antenna connections. They need annual
maintenance.
7) Consider adding dispensers for your tower grounds, too.
I used to engineer and install these things for the USN. Even with the
best of plans,
it was often a cut and try job, so hit the books and try to come up with
a planned
escalation program. Remember to change one thing at a time and not get
discouraged!
> What do you think? Would appreciate any knowledgable feedback.
I avoid all these problems by going QRP! < big grin!> Actually my
antennas have to be
better than most and I have had to do all of the above. We are in
limestone country
and have awful conductivity.
> End of RFI-Digest #59
Regards,
Jim Keyes, WA1TQG/5
An old salt beached in the Ozarks!
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