A Lightweight Portable Vertical

I bought a lightweight telescoping pole on eBay a while back. It collapses down to 26 inches and weighs less than 12 ounces. Best of all, I only paid around $10 for it. While it was advertised as a 7.2-meter pole (approximately 23.6-feet), it actually measures about 19.5-feet when extended. This pole was just begging for some sort of antenna to support.

After trying different types of non-resonant wires with it, I decided to build some sort of resonant antenna. For quick excursions to the field, I often take the AlexLoop. However, sometimes it’s nice to have something a bit more frequency-agile. I wanted something that is easy to deploy and could cover the 40, 30, and 20-meter bands.

I started off planning to build a vertical with a 16.5-ft radiator to make it resonant on 20 meters. I could then build some loading coils to make it resonant on 40 and 30 meters. In the end, I went a slightly different way with this antenna.

With the lousy band conditions lately, I spend most of my time on 40 meters. I decided to take advantage of the full length of the pole.  So, my concept was to use a 19-foot radiator with loading coils for 40 and 30. On 20M and higher, I would use the radiator as a random wire and use a tuner.

Schematic diagram of the matching network for the 19-ft vertical
Schematic diagram of the matching network for the 19-ft vertical

As you can see in the schematic, I feed the antenna through a 1:1 choke, consisting of 10 bifilar turns of #22 hookup wire on an FT140-61 toroid. I calculated the values for the loading coil using some online calculators (see notes below). From there, I went through several iterations of testing and adjusting to arrive at the final values. For the 40M loading coil, I ended up with 29 turns of #22 enameled wire on a T130-2 toroid. I made a tap at 11 turns for the 30M band.

Interior of the matching unit
Interior of the matching unit

I mounted both coils in a small box and used some small bolts to make the tap points accessible for band changing. I also made a little jumper with alligator clips to short out various portions of the loading coil for the different bands.

The matching network is attached to the pole with a small bungee cord. In this picture, the red jumpers are configured for the 30M band.
The matching network is attached to the pole with a small bungee cord. In this picture, the red jumpers are configured for the 30M band.

The pole won’t support much weight, so I built the 19-foot radiator from #26 Stealth wire (Part #534) from the Wireman. Because the pole is made from carbon fiber, I try to let the top of the pole bend over slightly, to keep the wire away from the pole. I don’t know how much influence the carbon fiber pole would have on tuning but I figure I’d avoid introducing another variable.

For radials, I used a 25-foot roll of cheap speaker wire and used it to throw together four 12.5-foot radials. Again, I grabbed what I had on hand and went with it.  While the four radials seem to be working out OK, I plan to add a couple more for good measure.

I should note that all the materials here were selected based on availability in my junk box. So, there’s certainly plenty of wiggle room here for experimenting.

I made up a little tripod adapter out of some PVC pipe. One end slides over the post on my tripod, while the other end slides up inside the bottom of the collapsible pole. I also found a screw driver with a handle that fits nicely inside the bottom of the pole. So, for ground-mounting, I can just shove the screwdriver in the ground and place the pole on top of it. This works surprisingly well and allows me to leave the tripod at home.

Vertical mounted on a tripod. My backpack is attached to the bottom of the tripod to help stabilize it in the wind.
Vertical mounted on a tripod. My backpack is attached to the bottom of the tripod to help stabilize it in the wind.

After considerable tweaking I ended up with SWRs of less than 2:1 across the entire 40M band and less than 1.5:1 across the 30M band. On 20M and higher, the tuner in my KX3 loads it up with no problems.

The vertical ground-mounted. The pole is light enough to be supported by a screwdriver shoved into the ground.
The vertical ground-mounted. The pole is light enough to be supported by a screwdriver shoved into the ground.

I’ve been very pleased with the results on 40M so far. It seems to radiate pretty well. I’ve also made contacts on 30M and 20M but, honestly, I need to use it more on those bands to get a better feel for the performance.  It’s hard to evaluate antennas when the band conditions are as poor as they have been lately.

Although the antenna works, there are a few things I would do differently, if I were to build another one:

  • My physical packaging could be better.  While the enclosure I used is nice and compact, it’s a little cramped for experimentation.  During development, coil adjustments were tough.
  • Separate coils for 40M and 30M would make the tuning much easier.  The tapped coil was a challenge to adjust.

I like the form factor and easy setup of this antenna.  I can set it up in a few minutes and it is very easy to transport by backpack or bike.  Now to give it some more air time in the field.

Time will tell if it’s a keeper.

72, Craig WB3GCK

Notes:

  1. Loading coil calculator:  http://www.k7mem.com/Ant_Short_Dipole.html   (Note:  The calculator I originally used for this project is no longer online.  This calculator should work.  Just use one leg of the dipole.)
  2. Toroid calculator:  http://www.66pacific.com/calculators/toroid-coil-winding-calculator.aspx

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10 thoughts on “A Lightweight Portable Vertical”

  1. Craig,
    I use a similar pole. When using my KX2, I use a 29ft piece of wire, mounted on the pole in an inverted L and fed at the base of the pole with a 9 to 1 Balun. No counterpoise. The KX2 tunes it 40m thru 1om. I’ve had great success on SOTA summits with this set-up. While there is some interaction with the pole, I’ve not found it to be noticeable. When using an MTR with no tuner, I’ve built a linked EFHW that is resonant on 17m, 20m and 30m. You have to get up to change bands, but its not bad. I also have, and I didn’t build it, a 5 band trapped EFHW, 40m-15m. I’ve used #28 teflon wire to further lighten the stress on the pole.

    If you have a KX3, with the appropriate transformer, you really don’t need the coils. It’s also a much simpler set-up.

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    1. Hi Mike. Actually my go-to portable antenna is a 29.5-ft wire and a 9:1 unun. I’ve also used the unun with this pole and a 19-ft wire. It worked pretty well on 20M and up on an NPOTA activation last year. I’ll have to give the inverted L a try, although the top section of the pole isn’t much thicker than the wire! Anyway, I haven’t built a resonant antenna in a while so I thought I do a little experimenting with this pole. Thanks for stopping by. 73, Craig WB3GCK

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  2. Hi Craig,

    Happy New Year to you and your family.

    Thank you for sharing the notes on this lightweight portable vertical antenna. I build this impedance match device and antenna elements. My three ground plane wires are 1/4 wave long on 20m. I ended up with 34 turns on a T130-2 toroid core. VSWR is less than 2:1 on the 40m & 30m bands and 1:1 on 14.310 MHz my preferred SOTA operating frequency. Shame I can’t attach a photo.

    I tune out the reactance on 40m and 30m with a homebrew QRP Z match.

    I have worked the east coast states of Australia (VK1, VK2, VK3, VK4 and VK7), South Australia (VK5) and New Zealand (ZL) all at 5 watts output power. 🙂

    Thanks for sharing this excellent antenna design and construction techniques.

    73, Andrew VK1AD

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  3. I see similar circuits a lot with part of a coil shorted. I would think that the coil acts as an auto transformer with one side shorted putting a lot of current in the short and hence quite a loss. At least it would affect the inductance of the non shorted winding. Is this not the case or how much loss does it introduce?

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    1. Hi David: Hmmm… I never really considered the tapped coil as an autotransformer. I just think of it as a smaller coil. The short has a lower impedance than the section of coil being bypassed. So the wire shorting the top end of the coil just adds a couple of inches to the radiator.

      I intentionally avoided leaving the top end of the coil unterminated. That would certainly look like an autotransformer, and I’m not sure what effect that would have. In any event, most variable inductors work by shorting turns. As for losses, I don’t really know; but if there are losses, they aren’t apparent in the way the antenna has performed for me over the years. Thanks for your comment. 73, Craig WB3GCK

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      1. I wound up a coil last night with multiple taps and put a varicap across it and hooked it to a VNA. I found that a short across part of the coil equivalent to the tuned section put a 2 to 3db loss. Doesnt seem like much on the typical DB stuff as its 3 not 10 or 20. But in terms of the real world 2db is still a third of the signal and 3db is half the signal. All the db stuff just hides the fact that 6 watts suddenly becomes 3 watts out. At higher powers something is going to burn.

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      2. David: Interesting stuff. However, I’m not sure your parallel circuit is a good representation of an antenna loading coil. Especially, if you are holding the frequency constant as you change taps. Might be interesting, though, to see how the Q of the coil is affected by the shorted turns, considering that different frequencies are used for each tap setting. Don’t know; just thinking out loud. Anyway, thanks for the comments and keep experimenting! 73, Craig WB3GCK

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