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SSB and Digital with… a QCX?

In January 2019, a ham named Guido, PE1NNZ posted to the QRP Labs groups.io group. The title of the post was “QCX-SSB: SSB with your QCX transceiver“.If you’re familiar with the QCX, then you’ll realize that this is a profound statement! The QCX is a high performance 5w CW transceiver. So how on earth did he get it to produce a SSB signal? He describes it on his GitHub page, and it’s far more extensive than I can write here. So, go check it out.

I’ll give you the short version: Guido put an entire SDR into an atmega328p, the same chip that runs an Arduino Uno R3. He is using the QRP Labs QCX as the basis for it, but already there is a community around it who is creating these radios without the QCX.

Since the BITX40 was cancelled and the the Easy BITX will cost around $100, there’s a gap in the sub-$60 SSB radio segment, and I was curious to know if the QCX-SSB mod could fill that hole. The only way to find out was to build one.

The Build Begins

The first thing I had to do was order a QCX. I did, and a week later it arrived. I also needed some parts that weren’t included in the kit: a 220nf capacitor, and two 82K-ohm resistors. Looking through the CB’s that I salvaged, I found one. The second one was made by combining two resistors in series from my resistor kit. The 220nf capacitor was another story. I grabbed a “221” capacitor from my capacitor kit and started building.

Trouble Begins

I went through the build manual from the GitHub page, and the radio seemed to work, but not without a major problem or two. First, there was zero sideband rejection. Second, there was no output in SSB mode! I spent hours going over the build, examining every single thing against the schematic. Eventually I found it: “221” is 220pf not nf! My solution was to remove the wrong capacitor and replace it with two 100nf’s (104) and two 10nf’s (103) from the QCX kit.

Wait- how is it that I didn’t need those parts for the rest of the kit? It’s easy: You don’t need most of the parts from the kit! The QCX SSB mod only uses about half of the parts that come with the QCX kit.

Once I fixed that, I got 3w output. Sideband rejection still wasn’t working, and it wasn’t until I forced the SDR mode of the software by editing the Arduino sketch that I was able to get it working.

As it stands right now, it’s still a work in progress. I have used it on 40, 30, and 20 meters and it puts out 3 watts. I’ve made both JS8 and FT8 contags with it, and one SSB contact on 40 meters. The audio report was good! Here’s JS8 over 24 hours with my L-Match tuner and a random length wire on my Jackite pole, with all of 3 watts output:

Please take a look at the pictures, and let me know what you think in the comments below. But first, some important notes.

Project Details

The the µSDX project (as it is now named) is not affiated with QRP Labs. While the project started with a QCX from QRP Labs, the QCX itself has changed and the µSDX developers are splitting away from using it as the basis for the µSDX build. As a result, it is currently a homebrew only project. There are some hams who have made their own PCB’s for the µSDX, and there is a lot of work being done on finalizing the circuit itself.

Is the µSDX ready for prime time? I’m going to say “not quite”. It has some issues that need to be worked out, but I think they be. There is some discussion about the PA and making it resonant on all bands. Currently, my radio has done 20m, 30m, and 40m, without trouble- but it’s still very much a work in progress, and the project is not yet mature. As it does mature, you can be sure I’ll be posting about it, so go subscribe to the site up above:

On To the Pictures!

Here are the pictures with comments on each:

The Soldering Kit

This build couldn’t have been done without my soldering iron, of course. I bought a Plusivo Soldering Kit recently and broke it in when building this radio. II have to say, it was really good! If you’d like to get one you can find one on Amazon. One of the things I liked the most about it was that it came with a great pair of tweezers, and also some solder. In fact, I used the solder for almost this whole build! It was less than $15 (it fluctuates a little) and well worth the price.

Thanks for reading!

5 comments

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    • David Wilcox on May 28, 2020 at 4:29 AM
    • Reply

    Hey Ryan,

    Thanks for your very interesting column and thoughts. Even though I barely understand what you are doing it does help my old brain to think. I really enjoy the enthusiasm you have for this hobby. I wish you were part of my radio club.

    All my best wishes and I hope and pray your wife is improving in her health status.

    Dave K8WPE

    • Doug W on May 28, 2020 at 8:07 AM
    • Reply

    Great article as always Ryan.
    So good that shortly after you posted Hackaday magically discovered it too…

    1. Thanks Doug! I may have had previous knowledge about when the Hackaday article was going to be published, and I may have less than coincidentally posted this one about the same time :p

    • Dmitriy on May 30, 2020 at 3:29 AM
    • Reply

    I made this mod with mine last year.
    many 40 and 20 groups ft8
    but when transmitting a loud sound in its dynamics

    de RX3DPK

    • Dana Marcy on October 2, 2020 at 8:08 PM
    • Reply

    I tried to build a qcx-20M early last year. I never got it to work. I damaged some traces!!!!!. I will have to remove many parts from my old board. Is their a list of test points that must be working for the modifications to work properly? Thanks in Advance. Dana Marcy VE6KBI, Canada

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