Low Cost, High Accuracy and Stability FST4W Transmissions Using the QDX Transceiver

In his presentation Gwynn Griffiths has shown how the spectral spreading information logged by the WSJT-x FST4W decoder can offer researchers new insights in to HF propagation.  While there are dozens of wsprdaemon KiwiSDR FST4W receive sites around the world already decoding and logging FST4W spots on all of the HF bands, there are only a few sites transmitting those signals.  The frequency accuracy and stability required by this use of FST4W means that existing low cost WSPR beacons like the widely deployed QRP Labs U3S and Zacktek cannot be converted to FST4W transmitters, and there are only a few very costly ham transceivers which come with external clock input ports.  However QRP Labs has recently introduced the US $70 QDX digital mode transceiver kit which, when paired with a Raspberry Pi running WSJT-x and a low cost GPSDO, creates a 80-20M or 20-10M transmitter which meets the requirements of this application.  It is to be hoped that the easy installation and low cost of such a system will encourage many more hams to deploy such beacons worldwide and thus expand propagation studies beyond North America and Europe.