My N6BT DXU-32 and AB-577 Military Mast System
A few years back I had a giant yagi up about 55′ on an AB-577 Military Mast. When my DXCC “work was done” I sold both. I have had the SteppIR UrbanBeam up just over a year on an ALM-31 crank up tower. Because the ALM-31 is not high enough for 40M low angle DX, I have been using my DXE DV-40-P phased array.
As chance happens lately around KY6R lately, I have come across an opportunity for another AB-577, and I will go for it. This coincides with the Bobtail Curtain project I have had in mind – but where I keep having trepidation’s about it because the center element would be way too close to the house and I’d have to basically cement a post in the creek bed – which I am loathe to do. I’d probably have RF in the shack and also have coupling of the center element with my rain gutter downspout. We also keep having trees falling around our house – mostly from neighbors yards, so I want to keep my antennas away from that mess. In fact – the two trees I used to hang antennas from are now both gone (they were very large old Monterrey Pines at their end of life stage – got dried out and had to be taken down as they leaned towards houses).
The higher angle plot is the UrbanBeam at 50′ – the lower is the DXE DV-40-P
Enter good old EZNec. I wanted to compare the Bobtail Curtain – with its 3 elements and 140′ “wingspan” to the UrbanBeam up 50′ – which is as high as I can get it where I can rotate it very safely and easily from the base. It has the same gain more or less as the Bobtail Curtain, but does have a higher take off angle.
The Bobtail curtain has a much narrower azimuthal pattern when compared to the UrbanBeam at 50′
While I would lose some low takeoff angle DX, since I only need Glorioso and Bouvet – and since the UrbanBeam will be “in the zone” on all bands 30M and above – it makes total sense to get the antenna higher than its present 31-ish feet. The major difference on 40M is that I can rotate the UrbanBeam – and I can’t rotate the Bobtail – which is its huge drawback. While its a really cool antenna that I would love to try – doing all that work to end up with a really narrow beamwidth – even at it low takeoff angle just isn’t worth the effort.
It is however, much more practical to put the UrbanBeam on this newfound AB-577.
Other benefits will be to get rid of three verticals in the backyard and have one antenna support. I can go back to an 80M delta loop that I had hanging off the tower – which you see in the above picture – fed with ladder line, and then I will have 80 – 6M, which is all I need. Its clean, practical and will also let me use the ALM-31 along with the AB-577 – and let me keep my antennas out of trees that keep falling down – or have to be taken down.
This time around I will keep the ALM-31 and the AB-577 and the UrbanBeam. These are all keepers.