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0 pointsparsimo20101y ago0 comments

Maybe earth shattering isn’t the right word, but this is a big deal for fans of QRP labs. The (tr)usdx is a bit cheaper hardware, which limits the performance. The QMX has a more powerful processor and will outperform the (tr)usdx by several dB in terms of distortion.

Hans (the designer) is an amazing developer and very thorough, and his kits are very high quality. He includes several diagnostic tools in his firmware, so you don’t just build a kit, but you can diagnose and tune the performance with the kit itself. A beta release from Hans is practically a release candidate in everyone else’s eyes because he’s so thorough.

In terms of functionality, this SSB mode means you can do practically any modulation now, where previously you could only do single frequency fixed amplitude modes. So now you can do PSK, winlink, SSB voice, and whatever modes become popular in the future.

Hans took a while developing this because he wanted to get the max performance from the tiny ~5W transmit power, so he implemented a technique called controlled envelope SSB which was clearly challenging to get right, and I’m not sure the (tr)usdx even has the processing power to implement it.

I’ll probably buy another kit because of this just because I’m so excited (I built a QMX+ last year). This makes the QMX a really good radio. It has always been high quality, it was just held back by only being able to do CW and a certain digital modes. Being able to do voice and ALL digital modes at this price range and quality is unbeatable.

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zbrozek1y ago· 1 in thread

There's a lot of unusual and flaky design in the boring plumbing parts of these things that makes them prone to self destruction. For example, using the MCU to make discrete buck regulators that power the MCU is a o.O choice that I think has no reasonable justification. There are perfectly wonderful multi output integrated chips with external synchronization that cost almost no money, take up less space, are more performant, and make it impossible for software to immolate the hardware upon which it runs.

Gifted embedded software, but the electronics is simply not that robust. The company could really use an electrical engineer to complement its software engineer.

parsimo2010OP1y ago

The QMX works well enough that I'm not going to critique the choice of voltage regulation or other plumbing bits. The boring parts work, even if they weren't designed by a professional EE. It uses low power on receive and is reliable, which are my primary concerns. I don't expect to get the same design as a team of Yaesu engineers would use on a $5k transceiver. If it's not hurting RF performance, then it is fairly low on the wish list.

Overall, the kit is still a killer value and buildable by someone who can follow directions and is decent at soldering. This is in stark contrast to many other kits which require a lot of sleuthing to figure out issues because the instructions aren't clear, or they changed some components and didn't update their documentation. And these other kits often don't have any better design for their power management sides either.

There have been a few board revisions to address some of the bigger issues that have come up with early board spins, and I like that mods have been made public for most of the early builders to keep their kits working.

The most common problem seem to be blown transistors from transmitting into a mismatched load, and that is mostly the operator's fault and common in many radios. I like that Hans put some SWR protection in the QMX to keep the finals from blowing as often as they might.