On Thu,1/22/2015 9:33 AM, Brian Carling wrote:
So the text books say....
However some of this is counter-intuitive
Science is not intuition.
and very counter-empirical.
When you add wire to an antenna, you change the antenna. When that
antenna is a "long wire" or vertical, anything connected to the chassis
of the radio becomes part of the antenna. These antenna types need a
counterpoise to carry return current for the long wire -- either a
resonant length of wire or radials. If we don't supply the return path,
the antenna will use whatever is available to it, connected to earth or
not. One of those accidental return paths is the green wire that is
part of the AC wiring in your home. It does NOT need to be connected to
earth to carry return current -- it's often long enough on it's own to
be an effective antenna. That power wiring will radiate your signal,
conduct it to equipment where it will cause RFI, and it will receive
noise. The only thing an earth connection does is change the length and
shape of that half of the antenna.
The same thing happens with antennas like a dipole when there is no
common mode choke on the feedline. The feedline, and everything
connected to it, become part of the antenna.
73, Jim K9YC
Best regards - Brian AF4K
On Jan 19, 2015, at 12:17 PM, Kelly Taylor <ve4xt@mymts.net> wrote:
In most cases, RF ground is a fallacy. The right length of conductor can
make it so that there's zero difference RF-wise between having it connected
and having it not connected to the ground rod. A ground conductor starts
rapidly losing effectiveness RF-wise at one-tenth a wavelength (about 6' on
10m) and longer.
Also, as part of an antenna system such as a vertical, a ground rod (for RF
purposes) is next to useless. (Important for lightning protection, yes, but
not for RF.) Radials are the way to provide RF current return: a ground rod
is mostly very well insulated from picking up return currents.
Dry soil has got to be less conductive than moist soil. I would think what
that means is multiplying the number of ground rods to make up for the lack
of conductivity, and perhaps encasing the rods in concrete or bentonite to
maximize whatever conductivity there is. You don't have to have the rods
vertical, either. You could lay them in trenches, and for concrete
encasement, you'd treat the ground rod much like you would rebar, suspending
it in the concrete during the pour.
73, kelly
ve4xt
On 1/19/15 10:45 AM, "Ken" <wa8jxm@gmail.com> wrote:
It seems to me that the ground above my rock layer (@ 36-40²) gets really dry
during the summer. Does that dry dirt have enough conductivity to be useful?
I do not know the answer to that question.
Are there different answers depending on why we have the ground rod? (RF
ground, power line ground, or lightning protection)
Ken WA8JXM
On Jan 19, 2015, at 12:53 AM, Kelly Taylor <ve4xt@mymts.net> wrote:
It seems to me a valid question to ask on this thread: Do you gain anything
by, for example, drilling a hole to get a ground rod deeper?
If you think about it, the answer might not be so simple.
The point of a ground rod is to maximize electrical contact with the ground.
If you have to drill 48 inches of an eight-foot rod and don't employ some
kind of conductive filler (concrete, bentonite, etc.) to bond the rod to the
rock, how much better off are you than just putting in a 48-inch rod? Even
if you do use bentonite, is rock a good connection?
If that's the case, what would be wrong with cutting the eight-foot rod into
two 48-inch rods and driving them 96 inches apart?
The point of eight- or ten-foot ground rods is to get eight or ten feet of
contact area, not necessarily to get eight or ten feet deep, yes?
Just curious on all this.
73, kelly
ve4xt
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