[TowerTalk] 1/4 wave vertical with counterpoise

[Jim Brown]

On 1/16/2026 6:01 PM, David Gilbert wrote:
> I'm pretty crummy at these videos (and they are often best watched at a 
> higher speed) so be gentle with me, but I'd appreciate any comments --- 
> pro or con --- on the content.

Very interesting work. It's important to realize that modeling software 
like this is looking at ground from its effect on the antenna and on how 
the antenna radiates. Your work looks very good. From everything I've 
read, a radial system DOES shield (screen) the antenna's field from the 
earth, and it IS a counterpoise, providing a low loss path for return 
current.

Some years ago, I saw a well developed discussion in one of the ARRL 
books (thought it was the Antenna Book, but looking just now can't find 
it in the editions of those books I haven't given away) saying that a 
well developed radial system DOES provide that screen. An example citing 
this effect, I did find just now in an older edition of one of these 
books was of K5PC, walking around under the 120-radial elevated system 
of a high power AM station with a battery radio and couldn't hear that 
station's signal.

So what I'm saying is that BOTH things are true.

Your conclusion about that mesh providing capacitive loading makes 
perfect sense. N6BT has designed and built a lot vertical dipoles with 
top and bottom loading. Following his lead, W6GJB and I collaborated on 
several 80M vertical dipole designs using top and bottom loading for 
county expeditions and Field Day.

I'm interested in how you built the NEC model for the mesh. I'm assuming 
all the wires connect to each other where they cross, so not easy to 
build the model. I can't think of an easy way to do it.

W6GJB has found a metal plate/sheet to be an effective counterpoise for 
ad hoc HF verticals, both experimenting at home and at his family's 
cabin in the Sierra. In 1977, Rob Sherwood published in Ham Radio 
Magazine a piece showing his use of wire mesh as a counterpoise over a 
small strip of soil, I think I remember between his driveway and his 
house. It was the sort of galvanized screen we'd buy at a hardware store 
for use in the garden.

I've gotten a lot of "light bulb" moments studying Rudy Severns' work on 
radial systems. He has studied the current distribution between radials 
and the resulting effect on total ground loss. You've probably seen it. 
He combined modeling with measuring real radial systems. Depending on 
where you live, the soil can be far from homogeneous. He showed that 
unequal current distribution increases total loss, and recommended 
making elevated radials slightly shorter than resonant.

There IS a lengthening effect (i.e., change in VF) for radials in close 
proximity with the earth, and it can be quite pronounced. I once did the 
experiment here of measuring the movement of the resonant frequency of a 
pair of 160M radials as a half-wave dipole. Comparable to what you're 
seeing as you moved the mesh.

When I suggested a few days ago that we can learn a lot from posting the 
plots for different conditions on the same axes, I want to show a couple 
of examples. Look, for example, at slide 24 in this pdf about 160M 
verticals and radial systems.

http://k9yc.com/160MPacificon.pdf

There are a LOT more such plots in http://k9yc.com/AntennaPlanning.pdf

Figs 2 and 3 show one of N6BT's 20M designs at 3 ft, 20 ft, and 33 ft. 
Subsequent plots show the effect of mounting height for different soil 
properties.

There are many other plots used to show the effects of changing one 
variable at a time. Fig 33 picks data points off of the plots in Fig 32, 
and plotting gain at four elevation angles vs height of a horizontal 
dipole for 40M. Fig 36 does the same for 80M.

Thanks for showing us this very nice work.

73, Jim K9YC