qrotx is a project that I have been working on over the last two years. In the ham radio world, QRO stands for "increase power" and TX stands for "transmit". I first had the idea for it when I read about the high resolution timer of the STM32G474 microcontroller, which can be used to generate signals at the frequencies of the shortwave radio bands.
During my first investigations, I found articles on Kahn's method[1] to generate SSB signals by splitting them into envelope and phase, among those "The Polar Explorer" by B. Machesney, K1LI and T. Brock‑Fisher, K1KP[2], and realized that together with the capabilities of the STM32G474, a very compact, simple, efficient, and low cost, but high power SSB transmitter could be built.
I have built a first prototype that has several design issues, but it allowed me to have a few QSOs on the 40m band with both AM and SSB. I am currently working on a second prototype to overcome the issues. I will share design files and code on GitHub under the CERN Open Hardware License (CERN OHL) and the GNU General Public License (GPL). Some work under construction is already there, but it is not finished yet.
Please see the GitHub project here.
If you have any questions, suggestions, or want to collaborate, please reach out to me at christian@riesch.at.
73, Christian K2CRI
[1] L. R. Kahn, "Single-Sideband Transmission by Envelope Elimination and Restoration," Proceedings of the IRE, vol. 40, no. 7, pp. 803–806, Jul. 1952.
[2] B. Machesney, K1LI, and T. Brock‑Fisher, K1KP, "The Polar Explorer," QEX, Mar./Apr. 2017.