Topband: Suggestions for vertical at HG0R

[Grant Saviers]

I agree with Dave's comments based on measurements and modeling of two 
different similarly sized top loaded verticals.

Grant KZ1W

On 11/7/2020 07:49, Dave Cuthbert wrote:
> 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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