Topband: NE7D loaded tower

[Steve London]

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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