Topband: Suggestions for vertical at HG0R

[Mail 10]

You can also alter the resonance by changing the slope of the top hat 
wires. If you can make them more horizontal, this will slightly lower 
the resonant frequency. Either make them tighter or move the ends of the 
supports further out. I have supports 3 m high, 40 m out from the 
centre. My top loaded vertical is 24 m high, originally fed about 2.5 m 
above the ground against elevated radials. Now it's fed at the ground 
level with a buried radial field (60 x 33 m), so the resonance was low, 
around 1770 kHz. I feed it across a 1000 pF capacitor to ground, and it 
presents a reasonable match across the whole band 1800 - 1875 kHz.

de VK3HJ

On 8/11/2020 2:07 am, Steve HA0DU 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
>
>
>