FW: Station grounding question

[Don Wilhelm-3]

Folks,

I received a couple questions, and perhaps I was not clear on one item where
the RF Ground occurs.

AN RF GROUND MAY NOT BE NECESSARY IN THE SHACK.  The proper place for an RF
Ground is at the antenna location.

Look at it this way - the half of a resonant dipole that is connected to the
coax shield looks a lot like what I described as a counterpoise, and in fact
that is just what it is.  In a similar manner, a radial on a ground plane
antenna also provids that low impedance RF Ground at the antenna feedpoint.
An on-ground quarter wave vertical on a ground screen, the screen serves as
the RF Ground, and a half wave vertical has a point of low impedance (RF
Ground point) close to its midpoint, etc - look at the antenna current
distribution to find where the current crosses from positive to negative -
that is a proper place for an RF ground point.  I may be simplifying a bit
here, because we do not actually have to connect these points to ground, but
they are at an RF Ground potential.  If you consider that an RF Ground is
relative to the other parts of the antenna, you will have a good part of the
correct picture.

When we bring an antenna feedpoint into the shack - either intentionally as
in the case of an end fed wire, or unintentionally as in the case of RF
flowing on the outside of a coax shield, then we must provide a return path
for that RF at the shack loaction, and a counterpoise wire terminating in
the shack is a possible solution.

So one solution for an operating position on a 2nd floor is to always use
balanced antennas and keep any extra RF off the outside of coax feedlines -
this puts the RF ground out at the antenna location where it belongs.

73,
Don W3FPR

-----Original Message-----

Glenn, Bob and all,

What constitutes a good utility ground or a protective lightning ground will
not always (you can substitute usually) provide an effective RF ground.  See
Vic Rosenthal's posting today on this same subject.

For example: Consider that a good RF ground can be provided by a properly
tuned counterpoise wire - an electrical 1/4 wavelength long and open at the
free end (just like half of a balanced dipole) and separated from earth
along its entire length.  The near end will present a low impedance at the
frequency the wire is tuned to and thus presents a good RF Ground.  This
near end can be (should be) attached to the tuner (or transceiver) grounding
point to provide the RF ground - THE CHASSIS SHOULD ALSO BE CONNECTED TO THE
AC MAINS AND LIGHTNING PROTECTIVE GROUND at the same point.

The point here is twofold: 1) Each type of ground will have different
characteristics, and 2) An RF ground need not have any relationship with
what we normally conceive as 'ground' - the British commonly use a separate
word - 'earthing' which I believe helps keep the distinctions separate and a
bit closer to correctness - earthing is good for AC, DC and lightning
grounds, but may or may not have any relationship to an RF ground.  I doubt
that a Ufer ground would serve as a good RF ground, although it may do so at
some particular frequencies - I would want to test it before depending on
it.

73,
Don W3FPR

> -----Original Message-----
>
> Hi Glenn
> Seems a lot of work for a relatively simple rf ground.
> Why not just take a piece of copper tubing and lay it in a shallow trench
> and bond your ground wire to it?
> RF doesn't penetrate the ground very far, so a deep trench wouldn't be
> needed.
>
> Glad to see you're still around.  Haven't heard you on in a while.
> 73, Bob N6WG
>
> -----Original Message-----
>
> I recently up graded my house electrical panel from 100 to 200 amp
> service. In order to do the up grade I had to install a Ufer ground
> which was 20 feet of bare #4 copper wire in cement. Our local code
> allowed a 10 foot run of wire in a U shape in a 9 inch wide trench. The
> wire had to be 3 inches above the dirt 3 inches from the side of the
> dirt 3 inches between the wires and three inches away from the dirt on
> the other side of the trench. That allows for 3 inches of cement all
> around the bare copper wire. The more I found out about Ufer grounds the
> better they seem to be to me. The PH factor in the cement and the fact
> that the cement never completely dries out and retains moisture make it
> an excellent ground.
>
> This leads me to my question. Is anyone out there using a Ufer ground as
> a counterpoise or to ground their tower and station? This seems way
> better than the old ground rod pounded in the dirt. Any comments would
> be appreciated.
>
>

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