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 !

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 Sandwich Hardware is free to built for every Radio Amateur for NON COMMERCIAL USE only. If you have commercial interests to produce a Kit or Product, please contact me.

uSDX / QCX-SSB Software Licence is currently 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.

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.

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