Topband: NE7D loaded tower

[Greg - ZL3IX]

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in 2005, but they have probably been archived by now.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
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>