Topband: Suggestions for vertical at HG0R

[Dave Cuthbert]

Steve,

*I believe there is a measurement error. *

1. The reactive part of the input impedance should not become more
inductive as the frequency is decreased. 1904kHz --> Z=68.1 + j0.3 and
1844kHz -->48.9 + j21.5.
2. An EZNEC model over 0.005/13 GND shows resonance at 1750kHz and the real
part of the input impedance to be 17 ohms. Real-world will be a bit higher
due to this being NEC-2.

So, the real part of the input impedance is too high and I don't think can
be accounted for by ground loss. Resonance is off by 150kHz.

Questions: How are you measuring the antenna base impedance?
                What instrument are you using?
                Are there any strong LF/MF broadcast station signals at the
QTH?

      Dave KH6AQ

On Sat, Nov 7, 2020 at 5:08 AM Steve HA0DU <ha0du at dx.hu> wrote:

> HI All,
>
> Today we finished installing a vertical with a top hat at HG0R, but it
> is not perfect (yet).
>
> The vertical part is about 20.5m (67 ft) tall, starts with 10m of 50mm
> (2") pipe at the bottom, and ends with 28mm (1.1") OD pipe on top.
>
> There are 8 quarter-wave radials below the antenna at each 45 degs, soil
> is wet black earth.
>
> Top hat wires are connected to a small aluminum plate. The four (4) top
> hat wires are about 12m (39 ft) long each, and are sloping at an angle
> between 60 and 45 degrees.
>
> We measured the antenna, and found the following:
>
> *1904 kHz*  (minimum SWR and also ain inflexion point in phase):
>
> *Z=68.1 + j0.3       SWR 1:1.36    Phase 0 deg*
>
> *1844 kHz* (resisitive Z closest to 50 ohms)
>
> *Z=48.9 + j21.5    SWR 1:1.54    Phase 23 degs*
>
> */One step before, with shorter top hat wires (approx. 10.2m wires) the
> SWR was lower at the 0 phase point, but it was at 2005 kHz./*
>
> Please tell me what shall we do:
>
> - tilt the antenna again, add more lengths to the top hat wires, so that
> phase 0 point comes down to about 1840 kHz (R will be still higher than
> 50 ohms), and add more radials, perhaps radiation resiastance comes
> closer to 50 ohms?
>
> - add a series capacitor to compensate the +j21.5 at 1844 kHz, and leave
> it as is?
>
> Or any aother suggestions?
>
> 73/DX
> Steve HA0DU
>
>
>
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