This short tutorial by WA3LTJ was created in benefit to those interested in this particular radio mode and service.
WSPR (pronounced like "whisper") stands for Weak Signal Propagation Reporter. WSPR is a ham radio operating mode used to map radio propagation paths throughout the world. At any moment, you can see where in the world one location can reach another on each high frequency (HF) band. Check out the live map of WSPR station connections. The map is created real-time and any ham can contribute. Download the WSPR software and use it to control your HF station (just like PSK31 or most of the other digital modes). Warning, run you radio at 1W or less! That's right, WSPR is designed for ultra low power. Stations with 100 mW (yes, 100 milliwatts, or 0.1W) share signal reports across oceans because WSPR is a special protocol for weak signal reporting. If you connect your station to the Internet, you can contribute to the live world-wide map. It is incredibly fun set up your station for 50 or 100 mW and see your signal reports from other countries. Weak signal operation is cheap, easy and exciting.