Topband: Misbehaving verticals (update)

[Dennis Ashworth]

Thanks for all who responded. I’ve taken the liberty of sharing my response
to Hank, K7HP who touched on many of the potential issues posted by others:

My comments are inserted below:


On Mon, Sep 19, 2022 at 2:03 AM hp <pfizenmayer at q.com> wrote:

>

> I wonder how much coupling between the top loading wires ??I guess you
> have looked at base
> resistance too with one or all of the others tied to the radials to see
> how much change 0
> or if you could  drop a couple of the top loading wires down next to the
> vertical so it would
> not be resonant . I am wondering about them looking like a parasitic
> element.
>

Interesting point. I believe the only thing I did to isolate the remaining
elements when testing a specific element was to open them at the base
(disconnect the ground system). I like your idea of dropping the top
loading wires. It certainly doesn’t hurt and may provide an important clue
if the impedance changes.

>
> You did not say what the element spacings were - if you have an EZNEC
> model for all 4  or just made
> a model of a couple you could play with seeing what the effect is.
>

The rectangle measures 144’x58’ (the array is for 80m).

I’m sure how the Topband list handles attachments, but I can share the
EZNEC model for the array off line if interested.

>
> Reason I am thinking about the coupling  is I have been doing some
> modeling of the effect of my 80M INV VEE on a two element  80M active vert
> phased RX array spaced as far away as I can get it in my yard and the
> coupling is incredible -the two el array is crap until I get the 80M inv
> vee effective "open" impedance  at INV VEE feedpoint to at LEAST 500 ohms .
>

The site is >120 acres of flat, arid land. Although there are many antennas
on the property, there are none within what I’d consider the near field.
The closest is a multiple element 160M vertical array, probably 3
wavelengths distant.

>
> Also I assume that you know about the issues with radials and "ground"
> with radials in EZNEC unless you go to the EZNEC4  with the license  or you
> can raise them an inch or so above ground and be fairly OK. Unless you
> raise the radials a tad in your model .
>

Yes. Here’s a helpful note from Terry, N6RY who modeled some of the ground
options/variables. Good work, and indicates to me that ground assumptions
made in the model above are probably close:













*“I modeled a single element from “your” array with 32 x 80 foot radials.
I used #12 for all conductors (including the mast) to get rid of errors in
NEC2 from mixing conductor diameters.Here are the variations of gain and
Z.  “Sandy" soil is 0.002 S/m, diel constant 10.  “Pastoral” is much better
at 0.01 S/m, diel const 14 (perhaps more likely for Beryl).Free space 0.68
dBi, 6.83 ohms  …  (and with zero loss conductors, the average gain is
-0.03 dB, which indicates the model is fairly decent).Radials 6” high,
Sandy     -0.58 dBi, 12.44 ohmsRadials 1’ high, Sandy     -0.26 dBi, 11.02
ohmsRadials 4’ high, Sandy     -0.26 dBi, 10.48 ohmsRadials 6” high,
Pastoral  1.02 dBi, 12.05 ohmsRadials 1’ high, Pastoral  1.09 dBi, 11.81
ohmsRadials 4’ high, Pastoral  1.10 dBi, 11.52 ohmsSo at least from the
NEC2 perspective, there’s nothing even close to 25 ohms and your mystery
continues.”*

I think what I’ll try next is to be absolutely certain the other elements
in the array are detuned electrically from the vertical under test. Stan
Stockton (call?) suggested adding additional radials to see if the
impedance drops. This probably makes sense too, once I’m sure the
decoupling mentioned above is complete.

Thanks all for the input!

Dennis, K7FL
Las Vegas