[Elecraft] Station grounding question

[Stuart Rohre]

Hi Glenn,
Let me jump in here and comment.   A Ufer ground is for 60 Hz and safety
grounding only.  It probably is not such a good RF ground, as that would
depend on its wavelength relationships, ie how big is it in terms of
wavelengths you use, what is it's capacitance to the dirt, what is the
inductance of its embedded rebar, what is your local ground conductivity.
How well are the rebar elements bonded to each other, and are they cad
welded, so that rusting of tie wires holding rebars is not an issue re the
resistance of the conductors?

Many hams probably confuse RF ground and earth/ safety ground, (or AC
grounding).  They are separate issues, although the RF ground should bond,
for lightning safety, to the AC ground per the National Electrical Code.
(All house grounds to be bonded).  A single ground rod has poor chances of
being low enough inductance and high enough capacitance to be adequate for
RF coupling to the earth.  Its area is too small.   Grounds thru an
intermediate medium, as the Ufer ground is, are also not the best candidate
to be an RF ground, depending on local conditions.

To have a good RF reference or counterpoise, we have to have a resonant or
near resonant conductor.  This is usually taken to be a quarter wave of
insulated conductor leading out from the chassis of the transceiver.  That
will lessen RF on the rig problems.  This can be used and then a simple
bonding of the rig to the other AC safety grounds can be used.  That keeps
your rig from having a greatly different voltage upon its case than the AC
wiring in case of lightning.

  If we have a connection to a rod, it does not have a good RF earthing
characteristic, because of the small area of the rod, the usually round
conductor used to bond the rod, and the length of the run of conductor to
the rod.   The grounding (RF) conductor must not be odd multiples of a
quarter wave for the band in use or you will have a high impedance possible
at the rig.

The goal in safety grounding for lightning mitigation is to spread out the
current from a strike or surge into the earth.   One such method that
satisfies the 10 ohm rule for AC earth grounds is 200 feet of bare no. 10
conductor put around the building perimeter.  It does not have to be buried
many feet deep, for it works by area in contact with earth.  Such an
extensive added earth conductor would augment your Ufer ground and give you
added protection by bonding to it.  Depending on the local state of earth at
your QTH, this may or not, be adequate for your RF ground.  The compounds of
the earth around you may be poor RF conductors.  In those cases, you
generally have to add more low inductance area to your grounding scheme.
Wide flat copper is one of the best conductors to use.  Plates can be
buried, and multiple rods are sometimes used.

Hope that distinguishes the two types of grounding you need for safety and
for low RF impedance to earth.

Stuart
K5KVH