Re-visiting the KY6R Lowband Vertical Array

Broadside pattern to the array:

I’m still very, very pleased with this antenna, and made the right decision at the right time. 40M and 30M have taken the place of 20M, and I am feeling like we have “shades of the bottom of Cycle 23” already in clear view. My 2 element 20M yagi is excellent – but the real action continues to be 40 and 30M.

The antenna is great on 160, 80 and 30M, which is a real “Holy Grail” when you live on a small lot. It is NOT a true 30M Bobtail Curtain, but models just like one – and is the first Bobtail – like array that really works gangbusters for me. I have wanted to have a working Bobtail since I first learned about them back in the early 2000’s, and now I finally have one. It is probably the 3rd time I’ve tried one, and now, after a couple of months of using it, I like it more and more every day.

It has already more than proved itself on 160M – which is what my original drive was. I truly am leaving DXCC HR #1 in the dust – and made two big decisions that were scary – changing my antenna farm and dropping my power level – but I’m in a new comfort zone with my station that feels great. I guess I am happiest when I have just enough to get the job done – but still wanted a killer antenna, because then the power level doesn’t matter as much.

The DXE DV-40-P phased 40M array plus this 30M Bobtail and the 20M yagi are exactly right for where we are at in the sunspot cycle, and I am especially looking forward to more and more 30M activity.

The telltale sign that you have a Bobtail is the azimuthal pattern. The beamwidth is more narrow than a half square, and there are the little “ears” at the side. N6LF has an article on how to eliminate these “ears”, but I’m fine with them. Just for fun, I modeled two verticals spaced 70 feet apart and at lengths between 43 and 70 feet tall (to see if what I have compares where maybe the horizontal wires on my antenna might be acting as just a phasing line), and NO – the horizontal wires are important. In fact, the two vertical wires in the middle are also very important. In a half square and a bobtail – the horizontal wires are just phasing with very little contribution to the pattern. Also – in a (true) bobtail, the “ears” are more pronounced. The configuration I have just happens to cut the side angle “ears” down to where there is little energy going that way – and where the concentration of gain is better than a bobtail. Part of this was a “happy accident” – I just modeled what would fit in my backyard – and with dimensions also influenced by what materials I had access to. The Spiderbeam masts were used after a 60′ vertical bent over – and so I wanted something super robust this time – and I am now much more confident in this antennas mechanical strength.

Several things have come together to make this a special antenna for sure.

The feed and dimensions are actually a little different than a “classic” Bobtail on 30M. The spacing is actually more in line with a 40M Bruce Array – 34 feet between each outer vertical element. The height of each vertical element is 1/2 wl on 30M. A normal Bobtail looks like this:

A normal Bobtail has 1/4 wl elements and spaced 1/2 wl apart. Also – the feed is an L feed, and I have what amounts to an open feeder set of wires – so its more like a dipole. I am NOT feeding it against radials – but there are 96 radials underneath – so I have a really great ground screen. I am sure that I have a lot less loss this way, and do think I am getting the qualities of a weird combination of a Bobtail and a Bruce Array.

MAIN LESSON: don’t be afraid to try something that deviates from what you read in a book or online. This antenna seems to have the best of a Bobtail and a Bruce Array. In fact, its gain is better than either, with a similar great DX pattern and takeoff angle.

So – I don’t know exactly what this is – maybe a “Hybrid”? Getting a really decent antenna to play well on 160, 80 and 30M is a pursuit I have had for years. Its not easy at all – and it took so many attempts to get to this point. Mother was the necessity of invention – and the Spiderbeam Aluminum masts – surplus to the VK0EK DXpedition and purchased used from the project was the impetus for this project. Also – at 58, I’m not interested in climbing towers or even going up on the roof as much as I used to be – so having all antenna maintenance from the ground or a short ladder is just perfect.

But its the most interesting antenna I have ever designed and built – maybe I actually have stumbled on something called the “KY6R Lowband Array”?



~ by ky6r on April 18, 2017.

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