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: [email protected] > Date: Thu, 29 Jan 2015 13:55:17 -0700 > To: [email protected] > 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 > > _________________ > > Topband Reflector Archives - http://www.contesting.com/_topband > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
