joesugar over at Computer/Electronics Workbench writes:
Because of my location, amateur radio operations are limited to low power and disadvantaged antennas. Therefore, the WSPR (Weak Signal Propagation Reporter) protocol immediately caught my eye when I first ran across it. My primary interest is building, so I put together a stand-alone beacon using an Arduino and AD9850 DDS module and ran it for a while on 30 meters but got tired of having to manually switch the antenna every time I wanted to go from transmit to receive. Eventually I decided what I really needed was a low-power transceiver I could dedicate to WSPR operations.