uSDX Sandwich

Introduction to uSDX

First of All: The uSDX is not a Product, you can buy. It´s not a Kit, you can buy and build. It´s a true (non commercial) Ham Radio Project, where you need to source your own PCB´s and Parts, if you want to build one. But the result is well worth the effort, as you will end up with a Multi-Band all Mode highly efficient QRP Transceiver !

UPDATE October 2021: (Chinese Clones)

with another Update November 2021, as it´s getting worse…..

In the last 3 months several uSDX (uSDR) have shown up on AliExpress and ebay. At that time Schematics and PCB Layouts clearly said „Non commercial use only“.  We know, that the production of those rigs costs them under 40 US$ (as we were in contact with them at that time, trying to get them on board somehow) and they are sold for between 140 and 170 US$.

uSDX is supposed to be a cheap entry level rig with great performance, that was created and published out of pure Ham Spirit. The fact that some backyard buisness guys are putting their high margin on it does not help with that original idea.

As a result, we wanted to shutdown the uSDX Project and stop development, which caused protest from the fans and followers. So we did the opposite: We applied a very open license to the rig:

Creative Commons License
uSDX Sandwich Hardware is now under Creative Commons Attribution-ShareAlike 4.0 International License.
This means , you can use the provided Design in any way you like. Even commercially.  However, if you use it, you need to mention the source and re-publish your files and changes under the same license !

In case of commercial use, a donation would be appreciated, but not mandatory.

Of course, non of the commercial profiters ever had the decency to donate a cent for the „free development“ of their profit.

They also did not re-publish their schematics, and from the measurements, that some buyers published (and meanwhile I could do for myself ->look for my youtube Channel DL2MAN), we could see, that they do not work well. It seems, they copied my published Class E part values which were calculated and optimized for a certain FET. They seem to have changed the FET without taking it´s effect into account. On top they added changes, but did not document them, so noone can help you in case of failure.

This means, those rigs, commercially sold from china

  • did NOT HAVE PERMISSION to be produced and sold 
  • do not even fulfil the new very open license conditions (mentioning source + republishing under same license)
  • Do NOT reach the uSDX Efficiency Standards of 80-90% (they are more in the 50-60% range, in some cases even 20%)
  • Do NOT fulfil the minimum Harmonic suppression legal requirement of -43dB (there were measurements done by group members, meanwhile by myself. Worst case was only -20dB below fundamental !!!)
  • Are way overpriced (3-4x of the production cost, at absolutely NO development costs, and no support for us, the developers)
  • Lack in overall production quality and documentation (Even their documentation was copied and pasted in great parts from Guido´s Github page up to the point of total confusion, because certain things do not apply and don´t make sense)
  • Will not be supported by me or Guido
  • Will absolutely not be supported by QRP Labs !
  • We were informed, that those chinese sellers even sent unhappy customers over to QRP-Labs for Help. That´s an absolute NO GO !

Our good friend Hans has a buisness to run, was friendly enough to support us along the way, but you cannot expect, that he supports non-permitted copies of a pruduct, that were derived from a product he sells (Buy the QCX Mini !)

So have that in mind before purchasing such a rig, and ask yourself if this questionable behavior of the chinese buisnessmen fulfils your definition of HamSpirit.  You will not get the original performance, you will pay too much, and you´re on your own in case of problems, that most likely will occur ! You´ll harm high ham spirit guys like Hans Summers (QRP Labs), that made working Kits at low prices for the masses possible. And last but not least: With every careless mail to me, Guido or Hans, requesting support, you´ll lower our own ham spirits. 

Don´t buy uSDX / uSDR form China. Period.


The uSDX Project started as „QCX-SSB“ Modification for Hans, G0UPL´s famous QCX Rig, which is a feature packed CW TRX Kit for only 50$. This original QCX was discontinued. (More later)

Guido, PE1NNZ developed Software and a modification for QCX (QCX-SSB), which drew my attention, while I was building the original QCX Kit. I was not really interested in SSB Modulation (I´m 99,9% into CW), but I wanted the DSP features, he packed into an 8Bit Microcontroller.

Sidenote / Personal Opinion: I am a believer, that the art of morse telegraphy is the only „true“ way for QRP communication. Yes, there are Digimodes (especially weak signal modes) availabe today, but your computer is doing all the work for you. CW on the other hand is a personal thing:  The oldest way of Radio-Telecommunication between 2 humans, encoded and decoded in their heads and not by a computer. Still very efficient, even with only 5 Watts of RF Power. 

I contacted Guido about his (back then still unknown) Modification, and out of this initial contact, we developed a friendship while exchanging ideas. For the original QCX-SSB Modification only half of the Parts were needed, so we talked very early down the road, that we want to have our own PCBs, to unleash it´s full potential.

Very soon after that, the uSDX Project was born, and I started with first PCB Designs. (Thanks to John, VA7JBE – who taught me my first steps) That developed further into the „Sandwich“ Design – the reason you might be here for. The uSDX was initially thought as a light SOTA Rig, that could be used for portable Operation. I already owned commercial QRP Rigs for portable use, but they are heavy and consume too much Power. (Fun Fact: My FT818 draws more current on RX, than the uSDX Sandwich does while TXing full 5W Out!) So my personal Interest was the high efficiency aspect of it.

Another important aspect of it, was to understand Class E and how we could make it „Multiband“. The Approach was rather Simple, by adding a Class E Circuit per Band, and switch them with relays. Understanding how to come up with reproducable Values for the class E Network was harder to achieve…. (Thanks to Bob, W9RAN for the constant and fertile exchange about class E)

The original Idea behind the „Sandwich“ Design was to stay as flexible as possible, since none of us knew where the journey would lead us. So I seperated the uSDX into 3 interchangeable units:

IO-Board (Input in Form of Knobs / Rotary / Microphone / Key and Output in Form of Display and Speaker)

Mainboard (The Name says it all. The core TRX is on there)

RF Board (This contains the Band dependend Filter(s) and the PA)

Latter developed from Monoband parallel resonance Class E (below 80% Efficiency) into 8-Band serial resonance Board, that covers almost complete Shortwave at an efficiency of 87-93%.


uSDX / QCX-SSB Software Licence is open source.

On the Pages you´ll hopefully find everything you need, to build a uSDX Sandwich. I´m constantly trying to improve this page and add new information.

Further Help can be found in our Discussion group:

To avoid the impression, this is a „one man show“: The uSDX is a software defined Radio. This means: My Hardware would be worthless without Guido´s brilliant Software. Guido, PE1NNZ and me are working 100% together on this. The software was permanently developed together and along with the hardware, as a result of constant exchange between Guido and me.

Another  (very popular) Hardware Version of the uSDX was created by Barb, WB2CBA. More here:

Hans has also recently released QCX Mini, a true artwork masterpiece. The kit includes a daughterboard to make the uSDX Modification easier. Modification instructions can be found here.

73 Manuel; DL2MAN