Building QRPBuilder’s QBV 40m/20m-10m antenna

Over the New Year holiday I built the QBV 40m/20m-10m Switched Portable Antenna, from a kit provided by QRPBuilder. This is the first kit I have built. I really enjoyed building this antenna. I was finally able to get it out into the field today (January 4, 2025) for a POTA activation and I’m really pleased with how it performed.

Here is my completed build of the QBV antenna. The antenna consists of a switched loading coil for resonant operations on 40m or 20m. When the switch is in the 20m position (upwards), you can operate on 17m to 10m with an antenna tuner.

After building the antenna a few days ago, I was finally able to try it out for a POTA activation and it performed really well on 20 meters with my KH1 radio at 5 watts. Here are the reverse beacon results from today’s activation. I’d say that it did very well for such a small, compromised antenna.

Building the antenna

I ordered this kit about 9 months ago in March of 2024 - I’ve finally gotten around to building it.

I am new to kit building of any kind. Here are some photos from my build.

An early step was soldering different lengths of magnet wire, for the coil, to the switch. I used a PINECIL soldering iron.

One of the most difficult steps for me was getting the switch into the tube and through the switch hole. Here’s a photo of the switch in tube, it’s out of position. I need to angle it upward into the switch hole.

It took many attempts. I had to be patient. A couple of times, my soldering connections broke and I had to resolder the magnet wire to the switch and try again. Finally, I got the switch positioned and through the hole without breaking my soldered connections.

Next, I wound the top and bottom magnet wire coils around the cylinder. In the photo below, I’m using a multi-meter to test the connectivity between the magnet wire ends when the switch is in different positions. My ALLOSUN pocket multimeter cost me all of $16

The coils are a large inductor which makes the antenna appear electrically longer in length. The coil allows the antenna to be shorter and more portable. When the switch is open, the whole length of the coil is active which increases its electrical length to operate as a 40 meter antenna. When the switch is closed, the lower coil is bypassed to decrease its electrical length and operate as a 20 meter antenna.

I soldered the end connectors on. Below is a photo of soldering the bottom, connector cap.

Below is a photo of soldering on the top which will connect to the whip antenna connector.

Here’s a photo of the completed coil, ready for testing.

Testing the antenna

I set up the antenna in my backyard to test. I was able to measure the SWR and it looked good in various settings. I did find that it is sensitive to the whip antenna’s length. Luckily its really easy to adjust length as it’s a 5 foot telescoping antenna. For 20 meters we want to antenna fully extended to 5 feet. For 40 meters I am adjusting it about 5 inches shorter.

Radio propagation was horrible that particular day. I tried to make some contacts and had no luck. Thankfully, today proved that it was conditions and not a problem with the antenna or my build.

Here’s a photo of how I pack the antenna. The bag and clamp fit nicely in one of my field pack pockets. The clamp is a CAMVATE C-Clamp for a camera.

POTA with my new antenna

Today (January 4, 2025) I brought the antenna and my Elecraft KH1 for a POTA activation. My son, Josh, had baseball practice (indoors) with his club baseball team and a POTA site, Dunstable Brook Wildlife Management Area, was five minutes away.

I clamped the antenna to the roof rack of my Toyota.

I was able to thread the feedline through the window and operate my KH1 from the my car.

The wildlife area is beautiful; I chatted with some hunters who had just finished their morning hunt.

The map below shows the contacts I made from the Dunstable Brook Wildlife Management Area in Tyngsborough, MA.

I’m pretty happy with how it performed today.

Final thoughts

If you read this and have any questions about the QBV 40m/20m-10m Switched Portable Antenna please reach out. I’m not sure what I’ll build next but I’m looking into different projects like the Michigan Mighty Mite CW Transmitter. Maybe that will be next.

I’d love to hear any suggestions if you read this and something comes to mind.