QDX digital transceiver

I brief description of a construction problem, symptoms and solution regarding the QDX digital transceiver from QRP Labs.

The “QCX+” (QRP Labs Xcvr +): a feature-packed, high performance, single band 5W CW transceiver kit with WSPR beacon and built-in alignment and test equipment. Available for 80, 60, 40, 30, 20 or 17m bands. Experimental use on 15, 12, 10 or 6m (lower power output and reduced sensitivity). For complete details see http://qrp-labs.com/qcxp  

The Optional enclosure is black anodized extruded aluminium, very sturdy and elegant. Front panel is 106 x 55mm and the depth is 146mm. The front and rear panels are drilled and cut to match the QCX+ with laser-etched lettering. The enclosure includes four self-adhesive feet. 

Optional Dev Board kit is pictured above (diagram only, as yet) in one of the above photographs and is described further below. 

Optional 25MHz TCXO module is pictured above (diagram only, as yet). In tests, the frequency change over the range 4C to 65C was +/- 0.25 ppm (parts per million). This is a tiny 14.8 x 10.5mm PCB with TCXO, SMD all ready-assembled, which is installed onto the main QCX+ PCB in place of the 27MHz crystal and 0.1uF capacitor C2. 

Hard-copy assembly instructions are not included in the kit. You need to download the assembly and operating instructions manual from http://qrp-labs.com/qcxp 

Note: The QCX+ transceiver is always shipped with the latest firmware version available at the date of shipment. 

Note: the optional GPS receiver module kit is very useful if you wish to operate this kit as a WSPR beacon (it disciplines frequency, time, and Maidenhead Locator grid square). It is also useful for calibrating the transceiver kit, to get the synthesiser reference oscillator precisely calibrated (resulting in accurate transmit/receive frequency). 

An optional 50W PA kit is available, which also has an optional enclosure. This 50W PA kit will give your QCX an extra boost for those occasions when you need a bit more power – to work a particular station for a regular sked when conditions are bad; to deal with our bad band conditions these days; to work a particular DX staiton, etc etc. The 50W PA kit includes solid state Tx/Rx switching for full break-in (QSK) operation. The kit includes heatsinks and connectors as well as the PCB and all components. See http://qrp-labs.com/50wpa for more details. 

List of features: 

  • Easy to build, two-board design, spacious 10 x 13cm board with main circuit and connectors, vertical front panel board with LCD and all-controls board-mounted
  • Professional quality double-sided, through-hole plated, silk-screen printed PCB
  • Choice of single band, 80, 60, 40, 30, 20 or 17m
  • Approximately 3-5W CW output (depending on supply voltage)
  • 7-16V recommended supply voltage
  • Class E power amplifier, transistors run cool… even with no heatsinks
  • 7-element Low Pass Filter ensures regulatory compliance
  • CW envelope shaping to remove key clicks
  • High performance receiver with at least 50dB of unwanted sideband cancellation
  • 200Hz CW filter with no ringing
  • Si5351A Synthesized VFO with rotary encoder tuning
  • 16 x 2 blue backlight LCD screen
  • Iambic keyer or straight key option included in the firmware
  • Simple Digital Signal Processing assisted CW decoder, displayed real-time on-screen
  • On-screen S-meter
  • On-screen real time clock (not backed up)
  • Full or semi QSK operation using fast solid-state transmit/receive switching
  • Frequency presets, VFO A/B Split operation, RIT, configurable CW Offset
  • Configurable sidetone frequency and volume
  • Connectors: 2.1mm power barrel connector, 3.5mm keyer jack, 3.5mm stereo earphone jack, 3.5mm stereo jack for PTT, 3.5mm stereo jack for CAT control,  BNC RF output
  • Built-in test signal generator and alignment tools to complete simple set-up adjustments
  • Built-in test equipment: voltmeter, RF power meter, frequency counter, signal generator
  • Beacon mode, supporting automatic CW or WSPR operation
  • GPS interface for reference frequency calibration and time-keeping (for WSPR beacon)
  • CAT control interface
  • Optional 50W PA kit
  • Optional aluminium extruded cut/drilled/laser-etched black anodized enclosure

Optional Dev Board kit

The development board kit is for anyone who wishes to experiment or modify their QCX+. The development board kit consists of a kit of parts including a PCB with the following features:

  1. High quality, double-sided PCB sized 95mm x 120mm (see PCB CAD exported diagram in the photos above)
  2. Through-hole plated holes with solder pads on top and bottom sides, on a standard 0.1-inch (2.54mm) matrix
  3. Ring of holes around the outside edge are all connected to ground
  4. Holes in the PCB are drilled to allow a screwdriver adjustment of the C1 trimmer capacitor, and the three trimmer potentiometers
  5. holes for fitting pin header connectors that mate with connectors on the main QCX+ PCB, for:
    a) Power (Gnd, +5V, 12V)
    b) Si5351A Clk0/1/2 outputs)
    c) I2C bus
    d) ISP header
    e) Frequency counter, DVM and RF Power inputs
    f) I and Q outputs (IC5 pin 1 and 7)
    g) I and Q path phase shift outputs
    h) CW filter input and output
    i) Audio amplifier input and output
    j) GPS header
    k) CAT control and PTT signals
    l) All pins of the PTT, CAT and Audio connectors

The dev kit consists of the following items:

  • 95 x 120mm PCB
  • 4pcs 12mm nylon hex spacer for mounting the PCB above the main QCX+ board
  • 8pcs 6mm M3 nylon screw 
  • 8pcs 2-way female header connector
  • 1pcs 20-way male header connector (may be broken into smaller pieces as desired)



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