[TowerTalk] Feedline (choke) question

[Jim Brown]

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