[TowerTalk] 1/4 wave vertical with counterpoise

Sat Jan 17 01:11:14 EST 2026

Thanks for the comments, Jim.

Well, the reason I don't think a radial system necessarily provides any 
shielding effect is that there is VERY little difference in either 
takeoff angle or maximum field strength between the case with the 36 
radials and the case with the mesh counterpoise ... both over the same 
very poor ground.  The differences were only 1 degree and 0.31 dB 
respectively.  If there was any significant shielding effect I would 
have expected considerably more difference, since the mesh covers far 
less area than the radials do.

But you could be correct ... that both effects exist.  I just think that 
if that is the case, the counterpoise effect dominates to a great degree.

Yes, I am quite familiar with N6BT's work.  I've followed his designs 
for at least a couple of decades, from his ZR design to his VOR concept 
(I think he wrote it up as a PDF file) to his other works.  I didn't 
notice it until after I had done my counterpoise investigations, but he 
has a new product out now called the Park-5. You can see it at N6BT.com 
and I am almost certain that those three tubes at the base are more than 
a supporting tripod ... I'd bet they are a "capacity hat" as well.  It's 
interesting ... as best I can remember, all of Tom's previous loading 
efforts involved some sort of folded or coiled linear element.  I think 
the Park-5 is his first product that as best I can tell uses a more 
capacitive loading.

Making the mesh was easy.  EZNEC has an option under the Create tab in 
the Wires panel to Create Grid.  You just specify the coordinates for 
three of the corners, the wire diameter, and the spacings. There is also 
an option to either connect the ends of the perimeter wires or not.

Yes, the proximity effect of the capacity hat to ground is so pronounced 
that I almost think it might be used to determine how deep the actual 
effective RF ground is in any particular location by matching the shape 
of the measured curve (resonant frequency versus height above ground) 
with the calculated one.  I'm pretty certain that EZNEC thinks the RF 
ground starts at the surface of the earth, but we know that isn't the 
case in practice.

Which by the way, means that a real life implementation of the mesh 
counterpoise I show in the video probably wouldn't be as sensitive to 
height above physical ground as I show ... simply because it would be 
functionally higher above the effective RF ground.  I probably should 
have pointed that out in the video.

73,
Dave   AB7E

On 1/16/2026 10:35 PM, Jim Brown wrote:
> 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
>
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