Building, Breaking, and Fixing: My Adventures with QRP Labs Rigs

 If you’re into ham radio and love building things, chances are you’ve heard of QRP Labs. Hans Summers and his team have created some of the most interesting kits out there, like the QRP Labs QCX, the QMX, and now the QMX+. These kits are small, powerful, and packed with clever design choices. But let me tell you—these rigs are not for the faint of heart.

Over the past few months, nearly 20 QRP Labs QMX and QMX+ radios have landed on my workbench for repair. Why so many? Well, these kits aren’t exactly “plug and play.” They demand precision, patience, and, most importantly, the ability to follow the manual to the letter. And yet, that’s part of what makes them so rewarding.

Kits That Fight Back (and Why That’s a Good Thing)

Let’s be real for a second—assembling a QRP Labs rig isn’t like snapping together LEGO bricks. It’s more like building a Heathkit back in the day, though with a modern twist.

For those unfamiliar, Heathkit was the OG of electronics kits. Starting in the 1940s, they sold everything from test gear to ham radios to entire televisions (seriously, look up the Heathkit GR-2000 25" Colour CRT TV) in kit form. Their manuals were famously detailed, holding your hand every step of the way. If you followed the instructions, you’d end up with a working piece of equipment that you could proudly call your own. The QRP Labs kits have a similar philosophy: follow the manual exactly, and you’ll succeed. Miss a step, and you might be scratching your head for hours—or calling someone like me to figure out what went wrong.

The QMX and QMX+ take this challenge to a whole new level. These aren’t just basic CW transceivers like the earlier QCX kits; they’re full-blown five-band rigs (or all bands 160-6 in the case of the QMX+) with digital mode capabilities. The design is ingenious, with everything from beautifully designed Class-E RF amplifiers to advanced filtering. But that complexity means there’s a lot that can go wrong if you’re not careful.

Common Pitfalls (and Why the Manual Is Your Best Friend)

Most of the repairs I’ve done have been due to tiny mistakes that snowball into big problems. Misplacing a single resistor, putting a diode in backwards, or skipping a calibration step (actually very few and far between on the QMX and most calibration is just to milk the extra milliwatts out) can lead to a rig that doesn’t transmit, overheats, or acts like it’s possessed by gremlins. Some of the most common issues I’ve seen include:

• Bad solder joints: The QMX and QMX+ use surface-mount components alongside traditional through-hole parts. If your soldering game isn’t strong, you’ll end up with intermittent connections that are a nightmare to troubleshoot. The enamel on the 0.33mm wire included actually strips off with the heat of the iron alone, but the cheap enameled wire I use when rewinding toroids is terrible and needs to be scraped. Another day I need to check whether my 0.4mm wire fits in the QMX with its densely packed toroids (it'll definitely fit in the QMX+, I replace ceramic capacitors with massive silver mica caps in those). 
  
  
  
• Power issues: These rigs are efficient, but they’re not forgiving of incorrect power supplies. Feeding them over-voltage DC (FOR THE LAST TIME: 12V MEANS 12V!! Not nominal 12v, actual fixed regulated 12v.) can cause all sorts of problems. Luckily it only draws ~800mA on TX, so a 7812 regulator will bring 13.8 down to 12v nicely. 

But here’s the thing—every one of these issues is preventable if you follow the manual carefully. I know, it’s tempting to skip ahead or “wing it,” but trust me, the manual exists for a reason.

What’s Inside These Little Powerhouses?

The QMX and QMX+ are marvels of engineering, especially considering their price. The rigs are built around a Cortex-M7 microcontroller, which handles everything from generating the CW signal to controlling the RF circuitry. The Class-E amplifier is a particularly clever touch, allowing for high efficiency without bulky heatsinks. The QMX radios actually use some plated part on the PCB as a heatsink, with a washer and nut to hold the faces of the BS170 finals to the board. Hans also designed it in a way that kept the cost low, but still allowed it to fit in a lovely aluminium enclosure like using separate PCBs for the display and headphone/cw key jack on the front. 

The filtering is another standout feature. Each band has its own dedicated low-pass filter, ensuring clean signals even when you’re pushing the rig to its limits. And the built-in alignment tools, while tricky to use at first, are a lifesaver once you get the hang of them.

That said, the firmware does have its limitations. While the QMX and QMX+ are capable of multi-mode operation, the current firmware is heavily focused on CW and basic digital modes like FT8. There’s talk of future updates to expand functionality, but for now, don’t expect these rigs to rival an Icom IC-7300 in terms of features.

Why Build One?

So, why go through the hassle of building a QRP Labs kit when you could just buy a factory-assembled rig? The answer is simple: satisfaction. There’s something deeply rewarding about making a radio from scratch, learning how it works, and then hearing your first contact come through on something you built with your own hands.

It’s a lot like something she once said to me when we were fixing an old printer together—she couldn’t understand why I’d want to spend hours working on something so stubborn, but there’s a special kind of joy in seeing something broken come back to life. That moment stuck with me because, honestly, it’s true of radios, printers, and maybe even life in general.

Closing Thoughts

The QRP Labs QMX and QMX+ might not be for everyone, but for those willing to put in the time and effort, they’re some of the most rewarding kits on the market. They remind me of the Heathkit days, where the journey was just as important as the destination.

And hey, if you ever get stuck, you know who to call. Just make sure you’ve read the manual first—I’m good, but even I can’t fix skipped steps.