Wednesday, June 08, 2022

Built the QDX from QRP Labs

The QDX v3 kit arrived yesterday and today I've finished the build.

This transceiver is tiny, about the size of a playing card deck. It does FSK modes on four bands: 80, 40, 30 & 20m. Five watt output and a great receiver from what I can see so far.

The QDX connects to a computer with a single USB cable that comes up as a sound card and does TS-440 compatible CAT control - so very convenient for possible field use.

It can be built for 9 or 12V operation - I went with 12V as I have it more available.

The assembly manual is the best I've ever followed. Clarity and detail with lots of handy tips from Hans. The board comes with all the surface mount components already soldered in place so the main job for the constructor is a few diodes, capacitors, transistors and winding the toroids. 

Page 34-76 of the assembly manual describes the design and could be a book on its own rivalling the recent Software Defined Radio Transceiver Book by Peter & Purdum.

I took my time and had a break after a few toroids. One of the joints didn't connect but following Hans' advice to check continuity found this problem at the time. On initial power up I blew a 25A fuse - which was a bit alarming - but I think it was my DC connector shorting. All was fine with another connector.

Running with wsjt-x on Ubuntu Linux 22.04 got immediate spots on each of the bands (shown here in WSPR Watch).

There is diagnostic software built-in that can be operated via a serial (over USB) terminal. Here is the low pass filter band sweeps on my unit. I'm interested to know if this looks normal or should I perhaps remove a turn from the 80m low pass filter for example?

Here's my portable operations configuration. The QDX is the smallest part:

I can't recommend this kit too highly.


  1. Hi Peter...Mayday?
    I am not very good on Linux.
    I just made my 2008 run UBUNTU. It runs well. My QDX is receiving but CAT control will not allow x-mit and the freq readout is red.
    The QDXruns fine on my work laptop surface PRO windows computer.

    error msg
    Hamlib error: IO error
    port_open: serial_open(/dev/ttyACM0) status=-6, err=Permission denied
    iofunc.c(81):port_open return(-6)
    rig.c(795):rig_open return(-6) while opening connection to rig

    Timestamp: 2022-07-23T11:43:31.901Z

    Any suggestions?
    de VK2AOE George

  2. Hey George,
    check that your user is in the dialout group.
    Use the groups command to check.

  3. Dear Peter
    tu tu tu tu tu tu tu tu tu.....I learnt about Linux users this morning. Did a who am I ....etc etc....reboot and :))))))))))))))))))))))))))
    73 and 88 VK2AOE ....I'm off to FT8 now!