Building the QCX-Mini (20m) from QRP-Labs

 

Building and homebrewing is a fun aspect of ham radio that I really enjoy. While looking to change up my equipment for SOTA and lighten my pack, I decided to build the QCX-Mini to take on harder hikes and see if I can use it as my main radio. After some delay getting the kit, it arrived the night before a day off. Perfect!

The kit and the enclosure with the shipping were $90. I like QRP Labs because they talk about why something is done and "teach" a bit as part of the build. The instructions are like 150 pages, but they make sure there are no misunderstandings through explanation and photos.

Just reading the "pre-info" before starting takes a while, but good stuff. The one thing they say over and over is that for the Mini to fit into the case, you have to be careful with all the positioning of components. In fact, there are parts where you have to clip off tiny "extra" pieces of a component for it to fit (we're talking about fractions of millimeters). Winding toroids has actually gotten to be pretty relaxing, although I think I shouldn't have followed the advice to burn off the enamel coating with the soldering iron and SHOULD have scraped it off as I normally do.

The build went steadily step by step and ending up going fairly quickly. It's easier than a number of other builds because all the resistors were factory installed being so tiny. After a hand full of capacitors, there's larger components, headers, and of course, the rest of the toroids. In order to get it compact, it also has three different boards that go together. There's the main PCB which is what you work on the longest, then there's the control panel which is interesting since you modify how they're installed to make everything fit. Finally there's the LCD display board. Fitting the parts together after the build is easy (before getting it in the case), which is what you do to do some of the testing.

So every builder knows about the moment of truth, the smoke test. This is when you plug everything you've done in and let power run through it. If you've done something wrong, or perhaps didn't solder well, or solder connected something it shouldn't, you see a puff of smoke (often a capacitor) that starts a LONG process of trying to correct the problem (if it's not just ruined). I passed the smoke test thankfully and the radio turned on. I went through a number of the initial settings (adjusting the display, setting the band, and testing input and audio levels). All ok. The next step was to get it all into the case, which means undoing all the connected boards.

As they mentioned, it's a tight fit. So even though it fit together outside the case, that's because I was

able to wiggle and work the boards, which you can't do within the case. So after a little bit of filing a few spots, clipping the very corner of one of the blue variable pots, I was able to get it to fit just right. I had it all together and in the case! From there more testing was required. I could hear signals coming in (a very positive thing!). I tried sending out some CQ's to check the Reverse Beacon Network. It was acting like a straight key, so obviously I needed to get into the menu and change some settings there as well. I finally got it all set and tried again. Nothing on RBN, meaning I wasn't getting out on transmit. I hooked up a watt meter--only .7 watts (supposed to be 5ish). Up to this point in the build (just further testing and troubleshooting left) took me about 7 hours. I have no idea if that's typical, but I followed the instructions carefully and double-checked each part and position.

This is when, after reading troubleshooting tips, I realized it most likely was the toroid wire and the enamel not allowing for an electrical connection--again, I should have scraped, not tried to burn them. OK, at this point, it's either take it out and redo it (cleaning up solder holes is not easy) or reheat longer to hopefully burn the enamel that wasn't removed before. I tried to heat the solder spots of the toroids, no change in wattage. By the way, in order to do that, you have to take it back out of the case again. I went back and forth a few times (got good at fitting in the case). In the end, after checking a few other possibilities, I still thought it was the toroid. I cranked up the wattage of the soldering iron, and did them again. This time I was getting 2.5 watts and tried RBN again and got spotted in WA. So, not 5 watts yet, but good enough to work and a success!

Thanks!

72, Mike AC0PR

Update 8/13/21 Some more adjustments, mostly to the toroid winding spacing on the bandpass filter, wattage at 4.4 watts now.