Which digital mode is used as a low-power beacon for assessing HF propagation?

WSPR stands for Weak Signal Propagation Reporter. It was specifically designed for probing potential propagation paths using very low-power (QRP) automated transmissions. A WSPR beacon transmits your callsign, grid locator, and transmitter power in a highly robust, low-bandwidth format. Receiving stations around the world decode these signals and upload the data to a central database via the internet, allowing operators to map current propagation conditions in near real-time. While PSK31 and MFSK16 are popular digital modes that perform well at low power, they are intended for live keyboard-to-keyboard chatting rather than acting as automated propagation beacons. SSB-SC (Single Sideband Suppressed Carrier) is an analog voice mode.