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uSDX (SSB with a QCX) Update

Earlier this year I wrote about a modification/hack to the the QRP Labs QCX called uSDX that turns a normal CW only QCX into a SSB capable radio. It uses the Atmega 328p chip as an SDR, and uses a high end technology call EER to modulate SSB out of an amplifier made for CW. I was quite excited by this, and purchase a QCX just for the purpose.


After much hackery, it worked!

And then it didn’t.

Not Success 🙁

I came into my shack one morning and found that there was no transmit or receive. I tried some basic troubleshooting, but… nothing. I shelved it for another time and hooked up my trusty TS-140 just to stay on the air.

I recently unshelved it and started doing some more involved troubleshooting. I found a bad front panel switch, and replaced that. From there, the radio receives, but does not transmit. I replaced the power amplifier mosfets (BS170’s) and there was no success.

For reasons mentioned below, I have decided to relegate the radio to “HF receiver” and stop working on it further. It’s not like me to give up on a project, so I’ll explain why I’ve made that decision.

Exiting the uSDX world

The uSDX is a neat experiment, and I really like how it takes a kit made for CW and beautifully hacks it into something new. The hack has limitations, of course. SSB audio quality is questionable, and the receiver performance is only sufficient- not necessarily good. Compared to my BITX40, I found it a bit deaf. The firmware as I used it was not very mature, and I had a lot of issues getting a full 4-5w output.

The uSDX community moved on to making custom PCB’s that are dedicated to making what’s essentially a new radio. It’s not a beautiful hack anymore, but rather a low end SDR transceiver that’s optimized for low current draw and small size for portable use. That’s great, but that’s not what I’m interested in. If that sounds interesting to you, then go check it out! If that sounds interesting to you, then go check it out! https://groups.io/g/ucx/topics

Since the community has moved on from the hack, I have decided to move on too. My next task will be to box up the receiver for casual use and leave it alone.

Why even write about it?

I want to make it clear that this post isn’t intended to bash the uSDX hack, product, or community- far from it! I wish them the best of luck. Instead, I think it’s important to recognize failures and shed light on how some of these communities and projects work. I went into this knowing it was experimental, and for me, the experiment ran its course. I learned a lot in the process and would do it again to gain the same.

All the same, knowing when to stop is just as important as anything else. For me, that time came and went. On to the next project. 73!


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    • Grumpy on October 21, 2020 at 3:33 PM
    • Reply

    I was in the same church — it now sits in a box and chocked up as another life experience. I believe it is like putting an 40 HP VW Beetle engine in a Porsche 911. From the outside looks good; but just not up to the task

    1. I like the analogy! This got me thinking thta the uSDX is a lot like little 3 cylinder cars. Nobody ever says that their Geo Metro is comfortable, great for long drives, or handles like a sports car. No, they say “It gets 40+mpg!” and that’s exactly what it is optimized for. The uSDX is optimized for low part count, low power draw, medium performance. For some people it’s great. I’m not one of those people, I guess :p

    • Ray Prada on April 2, 2021 at 11:38 PM
    • Reply

    A lot has happened since you wrote this Ryan. I think that Guido and Manuel are on to something. They’re not there yet but appear to be persisting. My hope is they ditch the 328 and unleash the new 4 dollar RP2040 Pico on the project, with its 125 MHZ clock and 12 bit ADC. What do you think?

    1. Indeed a lot has changed! Unfortunately I’m still seeing reports of the SSB on transmit not being so good. Once the project switches to new silicone, it won’t be a QCX based rig anymore- and that’s okay! When that happens I’ll be glad to re-evaluate it 🙂

  1. Ryan, Thanks for your honest report on this project. I have a QCX+ that I’m going to build for 40m and another QCX that I was going to use to make a uSDX. I noticed the changes in Op Amp gain, etc. and figured that I will just use the older QCX on another band or figure out how to convert it to a multiband transceiver. I haven’t done CW since 1947 so I want to get back to that. I’ll follow the people who are making the uSDX and see where they processorwise. 73, Jack W6VMJ Fort Collins, CO

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