Quarter-Wave Ground Plane Antenna

I followed calculations and instructions to build a quarter-wave ground plane antenna from some wire and a UHF connector that I picked up at the last Ham Fest in Harrisburg. I cut everything a little long and soldered it together. I trimmed the radials to about 54-inches and folded and rolled the radiator wire to a length that is resonant at 147MHz. I measured with the NanoVNA. Once it was at the right frequency, I found that bending the radials up and down could adjust the SWR at its lowest point on the graph. Keeping the radials slightly flatter had a lower SWR than the 45 degrees suggested in the original design.

This ground plane antenna feeds from the bottom, which is physically more sound than the vertical dipole I had up previously. I tested it last night when I strung it up, and it reaches Harrisburg and Parkesburg with no problem.

antenna  2m 


The Working Configuration

I’ve gotten APRS working with my current gear. I’m running my UV-K5 running egzumer 0.22.0 and VOX enabled. I set the radio volume pretty high, about 75%, and connected the BTech APRS cable and a USB-C 3.5mm audio adapter to my Pixel 6 Pro for an audio connection. The volume on the phone was set to nearly 100% volume. I ran APRSDroid in AFSK mode on the phone.

I watched for my position to show up on the map on https://aprs.fi/.

The Stuff That Didn’t Work

With nunu firmware, I needed to key it manually, but it worked. VOX didn’t work in the nunu 0.20.5, so I switch back to egzumer for working VOX.

Next Steps

I’ll next try to find an old phone to run the APRSDroid and try to use the Explorer QRZ-1, so I can dedicate some hardware to this project.