On 9/27/2025 1:25 PM, Brian Beezley wrote:
I think what's going on is that "current sink" means different things to
different people. I regard ground as an RF current sink, but not one of
zero impedance. That means that when a wire with current passing by is
connected to it, not all of the current in the wire will be shunted to
ground. A low-impedance ground will divert more current than a high-
impedance ground.
You've done a lot of great work to allow better measurement of soil
characteristics. We know that the upper surface of the earth (down to
hundreds of feet) is a big resistor. If we rig a vertical wire and tie
the bottom to the center of the coax and the shield to a ground rod,
we've added a big resistor in series with the antenna. Rr, the radiation
resistance, depends on the length of that vertical radiator. The
transmitter sees a simple series circuit consisting of Rg, the ground
resistance, the resistance of the wire, and Rr. The same is true of an
end fed wire.
We use a counterpoise -- that is, a wire connected to the shield at the
feedpoint to provide a low resistance return for antenna current. If the
wire is on or close to ground, current will be induced in the ground,
and loss from that current will show up as Rg.
Radials are a better solution. While current in the radials does couple
to the earth an produce loss, return current divides between the
radials. And since P is I squared R, loss is falling in proportion to
the number of radials.
When radials are laying on the ground and there are lot of them, we can
get away with it, but more wire on the ground is better.
N6LF has published a lot of great work, really scientific studies of
ground systems for antennas. His website is a great resource. His
discussions about this topic clarified a lot of concepts for me, and his
work is as important as yours, which is saying a LOT!
73, Jim K9YC
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