Friday, October 09, 2020

uSDX - Modern multi-mode SDR radio with class E output

Like many home brewers, I've been patiently waiting for the QSX from QRP-Lab. I hope it gets finished as it sounds fantastic and the QCX was such a great kit radio. 

In the mean time, clever Guido PE1NNZ, has come up with a modification of the QCX that turns a simple CW radio with class E output into a software defined SSB capable radio. The great thing is that it's open source and being actively developed. 

From Soldersmoke: "The SSB transmit-stage is implemented in a completely digital and software-based manner: at the heart the ATMEGA328 is sampling the input-audio and reconstructing a SSB-signal by controlling the SI5351 PLL phase (through tiny frequency changes over 800kbit/s I2C) and controlling the PA Power (through PWM on the key-shaping circuit). 

In this way a highly power-efficient class-E driven SSB-signal can be realized; a PWM driven class-E design keeps the SSB transceiver simple, tiny, cool, power-efficient and low-cost (ie. no need for power-inefficient and complex linear amplifier with bulky heat-sink as often is seen in SSB transceivers)."


There is an active discussion board about the evolving circuit and parts bill of materials (BOM) on groups.io here

There are two board designs, one is a "sandwich" that supports multiple bands, the other is a single board shown above. (Photo by Dan Reynolds posted in the group).

The CAD files for the board, now at revision 1.02 are available in the group and I found someone selling them on Ebay so I ordered there (currently sold out).

While I have some of the parts on hand I decided to order the full parts list from Digi-Key and this would normally be a tedious task but I've found the secret! Digi-Key has a feature called BOM management. 

  • From the files area on groups.io get the file “Bom_8397236.csv”
  • Log in to Digi-key
  • Choose BOM manager from the menu top right
  • Click upload bom, select the CSV file.
  • Adjust the column headers to make sure digi-key product codes and quantity are correct.
  • Click Add to BOM.
  • Click Add to cart.
    I got a few items which it said had “improved values” for. I just accepted them all - we’ll see how that goes.

    The order came to $64.52 which is over $60 so gets free shipping. In the end it was $70.97 including GST.
    They claim it will be here in 5 days which will certainly beat the board which is coming from EU.


    Manuel K has made a video showing how the transmitted SSB audio sounds at the moment:


    Here's Guido PE1NNZs original QCX-SSB off air recording:


    Interesting times in the home brew radio world. I hope Hans finishes the QSX soon or he may have missed the boat!

    2 comments:

    caulktel said...

    Hi Peter,

    I just received my V 1.02 boards also only mine are blue. As it turns out I had 90% of the parts in stock so I'm waiting for a few things from Digi-Key to finish it up. I look forward to finishing it and play around with it. Have fun.

    Joel
    N6ALT

    Clifford Heath said...

    After you build it, take a close look at the output on a spectrum analyser - you mightn't be so impressed. The class-E output stage of the QCX doesn't have very good amplitude control, so the uSDX is going to have issues with out-of-band transmissions due to that (and its limited phase rate - a limitation of the Si5351).