I can't speak with knowledge on stepper antennas. BUT I can regarding a Hi
Gain discovery III
I shunt feed my 105 ft. Rohn 25 with only the 3 element 40 meter beam as the
top loading.
More then once I burned a loading wire.... over the years I had that
configuration.
SO from that experience a complex antenna like SteppIR design I would be
VARY Leary !
Wayne W3EA
> From: n2icarrl@gmail.com
> Date: Thu, 29 Jan 2015 13:55:17 -0700
> To: topband@contesting.com
> Subject: Re: Topband: NE7D loaded tower
>
> I'm leary of shunt feeding a tower with a SteppIR on it. You are betting
> that when transmitting on 160, you do not end up with a high voltage
> point at any of the SteppIR motors that could damage them.
>
> 73,
> Steve, N2IC
>
> On 01/29/2015 10:07 AM, Tree wrote:
> > I spent yesterday loading NE7D's tower on 160 meters and thought I
> > would share the results here as a data point.
> >
> > His tower is about 75 feet of Rohn-25 with a SteppIR DB18E on top.
> > You can see a picture of it here:
> >
> > http://www.kkn.net/~tree/misc_pictures/NE7D-DB18E.jpg
> >
> > Rocky put down about 15 radials and I spent the afternoon trying
> > different gamma match attach points. We had a 600 pf variable cap at
> > the base. My initial attach point was around 55 feet - which in the
> > end - might have been just fine - but was not producing any good
> > results initially. I moved it down to around 45 feet and still had no
> > luck.
> >
> > My next step was to put a loading wire on top of the tower. I made
> > one about 55 feet long and this did change things. I did find I had a
> > very nice 80 meter antenna now - being able to move the resonant point
> > most anywhere on 80 I wanted. I then increased the length of the
> > loading wire to about 65 feet and put a second one up going the
> > opposite direction. I also put a gamma attach point up around 65 feet
> > and tried that. The results were better - as I was able to get a good
> > match around 2.1 MHz - but not lower. I decided to increase the
> > loading wires out another 12 feet or so - probably bringing them close
> > to 75 feet each - but things were still not very good.
> > Just for fun (or out of desperation) - I hooked up the 45 foot gamma
> > match wire again - and VOILA!! I was able to get a 1.2:1 SWR anywhere
> > I wanted at the bottom of the band. The 1.5:1 SWR points were about
> > 20 or 25 kHz away from the sweet spot.
> >
> > So - my conclusion - even with the SteppIR stretched out to the 20
> > meter position - it is not offering much in the way of top loading.
> > Perhaps there is a way to modify it to connect the parasitic elements
> > to ground to help with this - but this might be tricky as this model
> > allows any of the 3 elements to be driven.
> >
> > Our gold standard was a wire Rocky had up in the trees that he was
> > using on 160 meters previously. It was actually a pretty good looking
> > antenna - with about 70 feet vertical and then some similar length
> > horizontal.. The new antenna seems to be a couple of S-units better
> > so far - so I think it is working as it should.
> >
> > I hope this information proves to be useful for others. Keep an ear
> > out for an improved signal from NE7D on topband.
> >
> > Tree N6TR
> > _________________
> > Topband Reflector Archives - http://www.contesting.com/_topband
> >
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|
