Yes the distance to the tower has influenced the matching a lot ... besides
the 22.5 tower theres also two 80 meter sloopers and 1 inverted V 160 meter
dipole - altogether making the antenna electrical longer. Its a compromise
to get room for all the stuff up there :=) The 60 KHz difference in
resonanse frequence, to the calculated values, might be explained by all
this extra "top loading" capacity.
I will try repacing the wire, the SS wire can then be used as radials :=)
----- Original Message -----
From: "K9AY" <firstname.lastname@example.org>
To: "OZ1AXG Flam" <email@example.com>; <firstname.lastname@example.org>
Sent: Wednesday, September 24, 2008 11:44 PM
Subject: Re: [Antennaware] 160 meter 3/8 wire, steel or copper
> Based on your description and measurements, I am certain that proximity to
> the tower is affecting the impedance matching. I was able to obtain
> results modeling the tower about 30m tall. It will not have much effect on
> radiation, just matching.
> With your wire length, the feed impedance would be in the 30-ohm range.
> Ground losses might add several ohms, but would not double the impedance
> 70 ohms -- that is due to the capacitance between the wire and tower.
> At the present spacing, you may not be able to get a 1:1 VSWR with a
> capacitor, because the extra "capacitor" between tower and wire is part of
> your matching system, raising the feedpoint impedance. With more spacing
> between tower and wire (1.5m or 2m), the effects will be smaller -- and
> VSWR will not move as much in the wind!
> 1. Like the other guys, I recommend using copper wire for lower loss.
> 2. Add some short radials (as many you can) to reduce ground loss.
> 3. If you are able, increase the spacing between antenna and tower.
> 73, Gary
>> A question about wire ...
>> I have constructed a 3/8 for 160 meter. I use the tower to support the
>> antenna. It runs 22 meter vertically and then (horisontal for 24,5 meters
>> (i.e. total 46.5 meter). distance from tower is 1 meter.
>> A the base of the antenna it is feed with a serial capacitor of 430 pF (a
>> 330 in parallel with a 100pF : both door noob).
>> Ground is a combination of 4 ground rods and wire (space is limited).
>> swr @ 1860 Khz is 1:1.4. 1:2 bandwidth is app 80KHz. A noise bridse have
>> shown impedans around 70+j1.
>> Currently the wire is 1.5mm stainless steel wire.
>> How much would the antenna be improved if i substitute the SS wire with
>> 1.5mm braided copper wire?
>> I guess the seial capacitor would change as well ? any idea how much ?
>> Antennewire i use ( steel 40050 and copper: 40051):
>> OZ1AXG Flam
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