How does this work?

Each UberSDR instance analyses WSPR spots it has received and extrapolates the propagation data to predict SSB performance across Maidenhead grid squares and HF bands. This page finds your location (via GPS or GeoIP), then searches all online instances for the closest grid square they cover that is within your chosen radius. If that grid has an Excellent or Good SSB prediction, the instance is listed — meaning it is likely to hear you if you transmit SSB Phone at 100–200 W on that band. The highlighted rectangle on the map shows the matched grid square for each instance. If your location marker (YOU) is incorrect, you can click and drag it to the correct position — releasing will automatically re-fetch results for the new location.