7 Band Vertical Wire Antenna
Built it as a 6 band antenna, but I got a bonus band as well!
If you've been a ham for any length of time, you've know all about the fan dipole. Multiple wires extending from the feed point, each tuned to it's own band. That was actually my very first HF antenna; a 20m and 40m fan dipole hung off the back deck. I worked a lot of DX on that antenna!
Now (figuratively speaking), imagine taking half of that dipole and running the wires vertically, then laying the wires from the other half on the ground. Boom, you now have a fan vertical antenna! The concept remains the same: at it's resonant frequency each wire will have a low impedance at the feed point. Using my 20/40 meter fan dipole as an example, while transmitting on 20m the impedance at the feed point of the 20m wire will be low, while the impedance of the 40m wire will be much higher. The RF will take the path of least resistance and flow to the 20m wires. As I move higher or lower away from 20m, the impedance on the 20m wires will increase.
The same can be done with a vertical antenna. Fan verticals have been around for decades. In recent years, Callum McCormick (M0MCX) over in the UK has put together an amazing package of parts to create the DX Commander series of multi-band vertical antennas. He has perfected the construction and quality of materials to either purchase a ready to assemble antenna, or but just the pieces necessary to make your own fiberglass push-up pole into a DX Commander. A few years ago I purchased the pieces needed to use my 33' MFJ-1910 fiberglass push-up pole into a DX Commander. I use this antenna on occasion while portable, and have used it during Field Day. Great antenna! It's so nice to be able to switch bands and not have to adjust the jumper on the BNC coil.
I wanted to have a multi-band vertical at home again, but did not want to worry about the weakness of the MFJ pole in the high winds we get here, or with having the sections collapse on their own. All too often I read stories of people that have these somewhat permanently installed at home either breaking, or constantly having a section or more collapse. I have had the collapse happen to me many times while using the antenna portable. It's a PITA.
I have over 50 pieces of the 4' fiberglass military masts in the shed still, so I set out to build my own using these mast sections. So I drew up the guide plates, driven plate, and ground plate and had my water jet cutting neighbor cut them out for me. The bands to be included are 10, 12, 15, 17, 20 and 40 meters.
Considering I planned the antenna to only be 24 feet tall, the first 5 bands would be simple. Cut the wires to slightly longer than 1/4 wavelength, then tune. But at 24 feet, 40m would be a challenge. It would require loading at some point. So I went to a couple of my trusty coil calculators and found that I would need to add around 5 microhenries of inductance. This would require me to wind a few turns of wire at the 12 foot point to create that amount of inductance. In the photo of the antenna, you can see the coil of wire immediately above the first guide plate.
The radials for this antenna already exist. In the spot where it will reside is the location of my Hustler 6BTV antenna. I had previously put down about 32 radials of varying length from 30 feet to 6 feet, so all I needed to do was tie them into the ground plate.
I tried adding an 80m element to it (sloping inverted V), but this proved to be difficult to tune, so I removed it. I might either try that again later, or use the space where that wire ran and add a 30m element.
After an hour or so of tuning, I had all 6 bands tuned to roughly the center of each band. Once completed, I found out I had a bonus band available to me... 6 meters! I wasn't expecting that, but I found I had an SWR under 1.6:1 at both the SSB calling frequency of 51.125 MHz, and the FT8 frequency of 50.313 MHz. Both frequencies also precented an impedance of 45-52 Ω.
My Kenwood TS590S has 2 antenna inputs, so that makes it very easy to do an A-B comparison of this antenna with the 71 foot end fed horizontal wire in the front yard. As expected, some stations had a better RX signal strength on the wire, awhile others were better on the vertical.
The first day of using it I made FT8 contacts on every band the antenna was built for, 6m included. I worked a TON of DX stations on it, and some of them were made at a time when conditions were so bad I could not hear a thing coming from the radio! Switching antennas while receiving FT8 signals showed the new vertical was doing a much better job of pulling in the really weak signals.
I have very little money into this antenna. And to be honest, it could have cost me a lot less if I had used cutting boards for the spacer plates, and bought some scrap aluminum to make the driven and ground plates from. But I am very happy with how it turned out!
Next is to pull it back down, clean up the wires and shock cord, and paint everything. Painting the mast and plastic parts will not only help it to blend in to it's surroundings, but will help protect it from UV damage from the sun. Then heat shrink the spade connectors at the driven plate, as well as sealing up the back side of the SO-239 connector to protect it from the elements. I will also add some 'permanent' guy line to it.
