QFH Antenna Build

QFH Antenna Build

Last weekend I was at a cabin with a few good friends and we built the 137MHz QFH Antenna. The build was simpler and more straight forward than I had expected. Well, to be fair, one of my friends who helped out is sort of a human swiss army knife and we were well prepared.

All in all it came down to drilling a few holes, cutting down the rods and strips, prepping the wire, and assembly.

Top part of the PVC pipe with holes drilled

We drilled for a snug fit using a 6mm drill bit for the 6mm rods. Placing the holes far enough down so the pipe cap will fit but within reach for fastening the cable.

Bottom part with rods in place

After drilling the holes we cut the rods and fitted them to the bottom part. Leaving the top rods out until after we sorted the cable connection. A minor confusion resulted in the rods being a tad long, double what was needed, but they’ll get cut down once I have done some testing and tuning.

Cable prepped for connection

An RG58 was split open and soldered to some wire and one hole pieces of the metal strip. The center conductor connects to one half, and the shielding to the other half. At the other end of the cable there was already an SMA connector.

Top rods and cable fitted

We slid the cable into the pipe and fastened the prepped connector in place with the rods. Having the connection point ready to fit instead of trying to solder it in place was helpful as the end of the pipe isn’t very accessible.

Measuring the antenna with a VNA

After fixing the metal strips on the rods the antenna build was complete and ready for testing. I hooked up a NanoVNA V2 and fiddled around a bit. By adjusting where on the rods the metal strips sit I was able to get impedance of about 50Ω and low SWR. By adjusting the bend and shape of the metal strips I could manipulate the curve to get a sharper drop.

The QFH antenna on a tripod with home made waterproof housing

The location of the cabin is not great for satellite reception but we mounted the antenna anyway to try it out. It’s connected to a battery powered LNA and an FM band stop filter. The tripod is from a store that sells camera equipment and is intended for lights, those were more affordable than the camera tripods and would extend further up.

The 137MHz QFH antenna in all it’s glory

The initial results were promising, we got an SNR of around 25 from angles where the previous V-dipole was barely picking up any signal. However there was a lot of noise coming from a nearby tower and we were in a valley so we won’t know just yet how well the antenna performs.

The antenna is now at my home and awaits further tests and tweaks. Once I am satisfied the plan is wait for a window where the missus is out and then quickly mount the antenna to the back of the garage.

That’s it for now, over and out.