I have a problem.

It is probably a common one amongst hams but it takes significant amount of time, effort, and resources in my spare time.

……

I like to create/build/home brew things. Like…all the time.

Its a sickness (or so my wife thinks).

Anyway.

I have had a QRP Guys Portable Tri-band Vertical kit for a while, and it is a great kit that is easy to assemble and works great. It is small, lightweight, and provides 20/30/40 meter coverage. Run the radiating element up a collapsible pole and you’ve got a field antenna that sets up quickly.

Since I was raised an “Army Brat” and it was drilled into me from an early age that “two is one, one is none”, I never stop at having just one POTA/SOTA vertical antenna system.

My Super Antenna, CHA MPAS Lite, Buddistick, Wolf River Coils Silver Bullet, and others can attest to that.

I might have another problem – antenna addition!

After having spent some time researching options, I decided on the following factors being important to me:

  • No kit – I’ve done multiple kits and while I enjoy them and will still do more in the future, I wanted to build something more “DIY” than that
  • Lightweight
  • Multi-band (Ideally 20/30/40/60/80)
  • Most parts (if not all) are already in my possession amongst my surplus of wires, connectors, and such
  • Inexpensive in case I do have to buy anything (i.e. less than $10 USD) out of pocket (not including what I have already purchased for past projects)
  • Occupy some degree of free time 😉

I then settled on wanting a tapped coil design that would allow me to play with the tuning to find the sweet spots per band, and after looking at various home brewed ideas, I found SA2CLC‘s Vertical Antenna Loading Coil on Thingiverse.

Printing the Parts

It checked all of the boxes above and, after downloading the STL files, I begun printing the coil form and mounts. I have a couple of printers, but find that my Flashforge Adventurer 3 provides the most consistent ABS prints for me. I’m not a fan of the constrained print area of this printer, but it does do a good job at whatever I throw at it.

The photo above is about 90% complete. I have to give SA2CLC a lot of credit for an elegant design. No supports are needed to print this model, and it is well laid out and logical. Great work!

I chose to use ABS and printed the parts at 50% infill at standard quality. My goal here was to have a balance between weight and strength, with ABS widely used in products where durability matters.

About 15 hours later I had three parts; the coil form itself, and two mounts which allow you to affix the coil to a telescopic pole.

Upon completion of the print, I immediately realized a mistake on my part – I chose ABS for all of the parts, and the two mounts require some flex in the prongs so that they can be inserted into the body of the coil.

ABS doesn’t like to flex like some other plastics do, and I quickly snapped one prong off of the first piece I tried to insert into the coil, so I kicked off another print of just the mounts using PETG. That is what SA2CLC used and posted to his model page on Thingiverse.

That is another problem I have – reading the directions!

I then sent off a print to my Creality Ender 3 (I don’t have the higher temp nozzle to allow for PETG prints on the Flashforge – yet) and within a couple of hours had two new mounts that won’t break on me.

Assembling the Coil

In addition to the ABS/PETG printed parts, I used the following materials:

  • 1.25″ non-insulated alligator clips
  • SO239 chassis mount connectors
  • 18 gauge aluminum wire
  • 6-32 machine screws and nuts
  • 4mm binding post connectors
  • short length of 18 gauge wire to connect the center plug of the SO239 to the coil
  • ring terminals
  • aluminum tape (see below)

I followed the excellent YouTube video that the creator posted as a part of his model. The two places that I deviated slightly was first in connecting the ground for the SO239 to the binding post connectors. Why? I had seen this used in other projects online and had been wanting to apply it to a project of mine for a while, so I went ahead and added it here. Time will tell if this is effective or not, or even if it will stay put or not.

UPDATE: I found some thin sheet metal from some ducting work I had done previously that I decided would be more durable than the aluminum tape shown in the next photo. I cut out a piece that is roughly the same dimensions as what is shown below. As before, we’ll see how effective this is over time.

You can see the white PETG mounts on the bottom of the coil – one left and one right.

The second deviation was the use of another 6-32 machine screw and wingnut for the radiating element connection instead of a binding post as in the creator’s design. As with the aluminum tape, I may change that out but I’ve used wingnuts on multiple antennas and find them to be solid connections that are still quick to add/remove wires to. That is especially true when the wires use spade connections.

We’ll see how it goes in the field.

Stay tuned for Part 2 – Assembly and Initial Testing