Well, just to contradict all the nay-sayers who replied to this post, I
would like to say that I have been using my SteppIR 3-element as top
loading
for 11 years without the slightest hint of a problem. I did, however,
take
the precaution of grounding all the elements to the boom before ever
applying any RF. On the parasitic elements I soldered a wire to the mid
point of the brush, fed it out through a hole I drilled in the bottom of
the
motor housing, and connected it to the boom. On the driven element I
soldered a wire to the ground connection of the balun, and again fed it
through a hole and then on to the boom.
I did post some photos of these modifications on the SteppIR user group
in
2005, but they have probably been archived by now.
There was absolutely no detectable change in the antenna behaviour after
these modifications. I checked SWR and observable F/B quite carefully,
and
there was no discernible difference between before and after. (I was not
expecting there to be any).
Not only does the antenna add good top loading, but it is quite neat to
be
able to tune the match to different parts of 160, simply by changing band
on
the SteppIR.
73, Greg, ZL3IX
On 2015-01-30 06:07 a.m., 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
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