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Re: Topband: NE7D loaded tower

To: topband@contesting.com
Subject: Re: Topband: NE7D loaded tower
From: Herbert Schoenbohm <herbs@vitelcom.net>
Date: Thu, 29 Jan 2015 17:26:09 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
"More then once I burned a loading  wire.... over the years I had that 
configuration."  The solution for this is a wire cage as it does most of the 
radiating rather than the tower itself.  It is also easier to feed with a simple network 
especially if you find the sweet point tap.


Herb Schoenbohm, KV4FZ

On 1/29/2015 5:19 PM, Wayne Kline wrote:
   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
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