QDX: a feature-packed, high performance, four-band (80, 40, 30, 20m) 5W Digi-modes transceiver kit, including embedded SDR, 24-bit 48 ksps USB sound card, CAT control, synthesized VFO with TCXO reference. 

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The "QDX" (QRP Labs Digital Xcvr): a feature-packed, high performance, four-band (80, 40, 30, 20m) 5W Digi-modes transceiver kit, including embedded SDR receiver, 24-bit 48 ksps USB sound card, CAT control, synthesized VFO with TCXO reference. QDX transmits a SINGLE SIGNAL, it is not an SSB modulator with associated unwanted sideband and residual carrier, or intermodulation due to amplifier non-linearity. QDX outputs a pure single signal. 

The Optional enclosure is black anodized extruded aluminium, very sturdy and elegant. The enclosure size is 89 x 63 x 25mm without protrusions. The front and rear panels are drilled and cut to match the QDX PCB with laser-etched lettering. The enclosure includes four self-adhesive feet. 

List of features: 

  • Four bands 80, 40, 30 and 20m
  • Also works well on 60m, see John AE5X measurements https://ae5x.blogspot.com/2021/11/spectrum-analysis-qdx-on-60m.html 
  • 5W output at 9V supply (can be built for 4-5W at 12-13V supply)
  • Single signal transmission (zero unwanted sideband, zero residual carrier, zero intermodulation distortion)
  • Solid-state band switching and transmit/receive switching under CAT control
  • High performance embedded SDR SSB receiver with 60-70dB of unwanted sideband cancellation
  • Built-in 24-bit 48ksps USB sound card
  • Built-in USB Virtual COM Serial port for CAT control
  • Si5351A Synthesized VFO with 25MHz TCXO as standard
  • Easy to build single-board design, Professional quality double-sided, through-hole plated, silk-screen printed PCBs
  • All SMD components factory assembled
  • Connectors: 2.1mm power barrel connector, USB B (for audio and CAT control), BNC RF input/output
  • Built-in test signal generator and testing tools
  • Receive current 100mA, Transmit current 1.0-1.1A for 5W output with 9V supply (around 0.7A for 5W with 13V supply).
  • I-Q output mode if you wish to use a PC SDR program for demodulation rather than the internal SDR
  • QFU firmware update for lifetime free firmware udpates, easy installation on any PC without drivers, software or hardware e.g. programmer
  • Optional aluminium extruded cut/drilled/laser-etched black anodized enclosure (88.6 x 63 x 25 mm)

QDX also works well on 60m, as documented by John AE5X at https://ae5x.blogspot.com/2021/11/spectrum-analysis-qdx-on-60m.html. Outside the range 3.4-14.5MHz, QDX can be used as a receiver, with some loss of sensitivity. 

PC Software

Standard digi modes software like WSJT-X and JS8Call works fine with QDX, because QDX acts as a USB Sound card (for Audio) and a Virtual COM port (for CAT control).

There are three types of USB devices in QDX: USB Audio, USB Virtual COM port, and USB mass storage (like a USB Flash memory stick) for firmware update. Drivers for all of these types of audio device are already present on your PC if you are using Mac, Linux, MS Windows 10 or MS Windows 11. If you are using older versions of Windows, then you need to install a driver for the Virtual COM port (audio and USB Flash drivers are already present even on older Windows), the details are in the QDX manual. 


Here's a YouTube video about QDX: https://youtu.be/j6Vnh8eiEpg 

Here's a build-video series by Ryan W7RLF https://www.youtube.com/playlist?list=PLDP9oGiu60jJdiQOQx6-5DRn3l5GrfQQM (for Ryan's interesting website see https://miscdotgeek.com/)


The manual includes assembly instructions, operating instructions, design details, performance details

Manual (document version 1.06 published 10-Nov-2021)


QDX in its beautiful black-anodized extruded aluminium enclosure, CNC machined to suit the QDX and with durable laser-etched lettering:

These are screenshots of the built-in terminal applications, that may be used for testing, investigating, learning and configuration - but are not needed for operation of the transceiver. 

Selected performance measurements - see manual for full details...

WSJT-X operating screenshots


Please refer to the manual for the firmware update procedure, which is very easy and does not require any special hardware, software, drivers etc. It requires only a PC and a USB cable. Click the file in the first column of the table below, to download the firmware file of interest. Note that firmware files are encrypted and can only be used on the QRP Labs QDX. 

The downloads are a zip file; please unzip the file before copying the .QDX into the QDX. 

Firmware version history:

Version Date Contents
1_02 25-Nov-2021 - New "transmitter test" terminal application, lets you test PTT and Transmit
- New items in "Configuration" terminal application, let you disable transmit by band
- 'Log end' timestamp written at end of log, to indicate current elapsed time since power-up
- Bug fix: prevent log file overflow
- Bug fix: White noise intermittent on power-up is fixed
1_01e 25-Nov-2021 - Bug fix: Now AF and RF sweep terminal applications work
1_01d 24-Nov-2021 - Log entries now have a timestamp, HH:MM:SS since power-up.
- Error entries now appear in red, ordinary logging in white.
- Startup log entry "START" appears in yellow.
- Bug fix: Occasional CAT communications dropping should not happen anymore.
1_01c 12-Nov-2021 - Status LED flashes more info during TX to aid audio debugging on PC:
  3 flashes means all OK, TXing power;
  2 flashes means transmit mode, but audio level (volume) is too low;
  1 flash means transmit mode, but there is no audio at all
1_01b 08-Nov-2021 - Apply validation to config ref clock to make sure 25MHz +/- 1kHz.
1_01a 05-Nov-2021 - Bug fix: RX did not work after changing bands, until you changed freq again, or TX then RX again
1_01 27-Oct-2021 - IQ Mode, if enabled, transfers raw I & Q data to the PC for SDR programs.
- Japanese band limits mode, if enabled, prevents transmission outside Japanese band limits.
- Prevent QDX trying to transmit outside the range 3.4 MHz to 14.5 MHz, to avoid damage.
- CAT command MD can be used now to set mode LSB or USB
- CAT commands Q0, Q1 to QB allow get/set of all parameters on the Configuration screen
1_00_003 11-Oct-2021 - Initial firmware release for QDX.