K1JT's WSPR webpage. Joe Taylor K1JT is the person who created modes such as JT65.
"WSPR implements a protocol designed for probing potential propagation paths with low-power transmissions. Each transmission carries a station's callsign, Maidenhead grid locator, and transmitter power in dBm. The program can decode signals with S/N as low as -28 dB in a 2500 Hz bandwidth. Stations with internet access can automatically upload their reception reports to a central database called WSPRnet, which includes a mapping facility."
WSPR2 is essentially an attended beaconing mode which sends a series of 6Hz wide FSK transmissions some 1400-1600Hz above the nominal USB dial frequency. The data sent includs callsign, QTH locator and TX power. The burst lasts just under 2 minutes. The software then switches to RX a listens in the same 200Hz wide band for similar transmissions. When any signals are successfully received and decoded, the logs can be automatically uploaded to a web page where all users can see them. So, you can see who is picking up your signal and how far they are away. As the system can work with very weak signals because of its clever signal processing, QRP powers only are needed. Indeed this is an ideal mode for QRPp experiments down to mW or uW levels. Accurate timing is needed and it is usual to control the PC's clock from an internet timer server such as that available freely from www.atomic.com. In my own case with an old laptop, I update the PC clock every few minutes, but this may be far too frequent in most cases.
WSPR15 which will successfully decode signals buried even deeper in the noise, but each burst is 15 minutes long. Because of the long transmission period it is essential that transmitters are adequately rated and frequency stable: even a small temperature rise may move a crystal controlled signal many Hz.
The typical WSPR PC screen is shown here. The DOS like terminal window shows the port settings for audio in/out. WSPR Spots database is more useful online data showing all received logs and these can be filtered by callsign, band, etc.
This is a typical page on the WSPRnet internet page. It shows reception reports for 137.5kHz, in this case my own 30uW ERP beacon transmitted with a pair of earth-electrodes 20m apart in the ground! G8HUH is seen copying my signals weakly at a distance of 250km!
WSPR15 uses the same USB dial frequencies but place the TX frequencies in a band 25Hz above the 200Hz wide band used for WSPR2.
K1JT's WSPR download site .