Dave,
It was a good video. Don’t sell yourself short.
Most of my verticals have been 40 or 80m ones from ZF with the verticals pretty
close to the water. In most cases I use two elevated radials parallel to the
water’s edge. The vertical may very well be paced off; not measured with a
tape measure. The radials are then used to tune the resonant frequency.
Increasing the length or putting them closer to ground will lower it and making
them shorter or higher will raise the resonant frequency. In all cases I try
to have them off the ground by at last 4 feet or more.
I guess the measuring tape might come in handy sometimes, because if I have
made the vertical a quarter wavelength, I’ll end up using a hairpin to get the
R up to 50 ohms and if I’ve made it a little long I can sometimes eliminate the
hairpin and achieve a really good match just by changing the radials lengths or
heights.. Regardless of what you do, if you have a vertical really close to
the water with a good SWR, it’s usually a winner.
73…Stan, ZF9CW
> On Jan 17, 2026, at 1:15 AM, David Gilbert <ab7echo@gmail.com> wrote:
>
> 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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