Topband: NE7D loaded tower

[Tom W8JI]

Yeah, but you grounded the elements to the boom, which makes a bad thing 
into a good thing. :)




----- Original Message ----- 
From: "Greg - ZL3IX" <zl3ix at inet.net.nz>
To: <topband at contesting.com>
Sent: Thursday, January 29, 2015 9:22 PM
Subject: Re: Topband: NE7D loaded tower


> 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 2005, but they have probably been archived by now.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
>>
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