Over the weekend I was disappointed that I could not contact any of the many SKCC WES stations on 15 meters because I could not tune any of my antennas for 15m. My 80m loop was on the ground, and nothing else would work on 15 meters band. Until I get the tower up and the StepIR fitted to it, I have to rely on my 80m vertical loop for 15m. While it has worked well for PSK on 15m to Asia and Europe, it has not been much use for other directions, and it has a tendency to spend more time on the ground than in the air due to its tree top mountings. So having a useable antenna for 15m is a high priority. When I made my 43ft vertical, I didn’t really consider whether it would be any good on 15m, and as it turns out, I can’t get a match on 15m. While investigating other antennas for 80m, I accidentally came across an article titled A High Performance 1-wire DX Antenna which describes a vertical antenna of 32.3 feet length. At this length the antenna works well on 40m, 20m, 15m, 17m and 10m. Since I had reason to pull my vertical down for repairs, I decided to test this 32.3 foot length.
My vertical uses a Spiderbeam collapsable fibreglass pole. The vertical element of total 43 ft consists of aluminium sailboard mast and a wire running the length of the fibreglass pole. It is fed with a DX engineering UNUN designed for their verticals. I also had a trapped vertical for my work radio on this pole, and decided to remove it, as I no longer have use for it. The spiderbeam pole is I think 12 meters long and is mounted on about 2m of aluminium sailboard mast which is in turn attached to a 2 metre high timber pole concreted into the ground. Thirty-two elevated radials about 1m above the ground radiate out from an aluminium ring on this timber pole. The aluminium sailboard mast was part of the 43 ft vertical antenna element in this installation.
With the wire cut to 32.3 feet, I now had excess fibreglass pole, so I decided to use the aluminium sailboard mast as part of the radial system rather than as part of the vertical element. This would allow me greater overall height. So I attached the UNUN higher up the pole at the base of the fibreglass and connected the wire element directly to the appropriate terminal of the UNUN. I then used the woven copper metal strap (supplied with the UNUN) to connect the top of the aluminium sailboard mast to the UNUN . The other copper strap which had been used to connect to the vertical now connected the base of the sailboard mast to the ring for the radials.
What I now have is a vertical antenna that is resonant at the bottom of the 40m band and has theoretical SWR of 1.7:1 at 7300 kHz ( we will test later), it is a 5/8 wavelength vertical on 17m (which I can’t use yet) and 3/4 wavelength vertical on 15m. Now I know a 3/4 wave antenna is going to have a high take off angle but it beats my current setup.
I made a few hardware modifications to ensure minimal maintenance in the future and then raised the antenna for testing. I’ll use the antenna analyser later, but for now I just checked that I could tune on all the bands I wanted, especially 15m, which it turns out, I could do. Antenna analyser results will be added to this blog later.
Shack of VK2KMI 