The Radio #

I bought this little QRP Labs QDX kit back in May. It finally arrived a couple weeks ago and I’ve been dying to build it and take it for a spin. I finally got the kit completed and took it on it’s maiden POTA activation at Jonathan Dickinson State Park this weekend.

First, let’s talk about the radio. It’s a unique design that works not by generating an SSB signal, as a traditional HF radio might. Instead, it generates a single frequency at a time. It’s basically a CW transmitter but with a frequency that can change rapidly to match the frequency to be transmitted. If you’re interested in the nerdy details, they have a great write up in the assembly manual located here.

This approach only works for Frequency Shift Keyed modes. The popular FT-8 and WSPR modes, as well as RTTY and a bunch more will work with this transceiver. Modes that require multiple tones at once like certain digital software modems, and anything that requires phase-shift keying like PSK31 will not work with this transceiver.

On receive it uses an SDR frontend that implements a standard SSB receiver. The radio can also act as an SDR for the computer by exposing the raw I and Q samples to the computer

Here’s a shot of the radio completely built

Did I mention this thing is tiny? It’s about the size of a deck of playing cards. You can build it for 9V input or 12V input. I opted to go with 9V and use a DC-DC converter to bring the 12V of my battery down to 9V for the radio. I haven’t measured the output power, but it’s supposed to make 5 Watts at full voltage, but will work down to 7V at reduced power.

The Park #

I didn’t realize this before going but Jonathan Dickinson State park was originally commissioned as Camp Murphy, an Army Signal Corps training site in WWII! The radio heritage of the park was a really cool thing to learn about.

The Activity #

Here’s the setup for the day.

I have my MacBook Air running WSJT-X, the QDX, an absolutely overkill 24AH LiFePo4 battery, and the trusty Wolf River Coil SB-1000 tuned for 20M. Not shown is my NanoVNA, playing the role of antenna analyzer.

The QDX doesn’t have an SWR bridge or any protection for the power transistors. To keep from cooking my finals, I made sure to get the antenna relatively well matched before hooking up the radio.

It wasn’t long before I was making contacts, I think 20 meters was especially good that day because I was making it all the way to Europe on 5 watts! But it also wasn’t long before the rain started to creep in and threaten to end my radio outing early.

I was 2 contacts shy of the 10 I needed to activate the park when I decided to move the station into the car. I knew the rain would be here at any moment and time was of the essence. I don’t have pictures of the ensuing chaos, but I managed to get set up in the car just in time for the rain to start. I closed out the day having made 12 contacts. But the coolest thing by far was logging my furthest contact yet, with LZ1LZ in Bulgaria, over 5600 miles away!