WSPR or as it is pronounced, “Whisper” is a software set that is used for weak signal communication between amateur radio stations. In fact the letters WSPR stand for Weak Signal Propagation Reporter.
Unlike normal amateur radio communication, WSPR enables amateur radio stations to participate in a world-wide network of low power beacons. It enables an amateur radio transceiver to send and receive the WSPR signals and then upload the data to a real-time server where the results of the signals sent and received can be seen.In this way, WSPR forms a rather different form of amateur radio digital communication mode where the propagation paths that are open can be seen.
WSPR is a software application which was created by Joe Taylor, K1JT, a Nobel Prize-winning Princeton physicist who also developed another digital mode for amateur radio called WSJT.
Although Joe Taylor launched WSPR, it is now open source and is managed by a small team of radio amateurs.
WSPR was first released in April 2008. It uses a transmission mode called MEPT-JT. MEPT stands for Manned Experimental Propagation Transmitter and the JT represents the initials of Joe Taylor himself which also appear in his callsign.
The station needs to be manned to ensure that the operation of WSPR meets the licence conditions of stations around the globe. IN many countries remote or unmanned operation is not allowed, even if the station is totally automated.
Once the WSPR station has been set up and is running, operation is totally automatic, requiring no intervention. The WSPR software logs all transmissions as well as stations heard and with whom signals have been exchanged.
The WSPR software runs the transmitter / receiver as well as generating the signal and logging the stations heard and copied, etc.
WSPR transmissions use frequency shift keying, FSK: the signal has a very small shift and a very slow signalling rate. As a result of the characteristics of the signalling the actual signal occupies only about 6 Hz. Accordingly a large number of stations can operate within the 200Hz WSPR window without causing mutual interference.
Each transmission must be synchronised to WSPR time - transmissions start at the beginning of each even-numbered minute and they last for just under two minutes. Synchronisation is important, and to achieve this the clock in the computer controlling the WSPR transmission must be accurately set. Fortunately this is not difficult to achieve, especially as it is often achieved automatically and accurately. It can also be undertaken manually as well.
The WSPR transmission contains a fixed amount of date including: callsign of originating station, Maidenhead locator, power (in dBm). The callsign must have a standard format and therefore it is not possible to use special even callsigns with non-standard formats, along with callsigns with appended prefixes and suffixes, e.g. F/G3YWX, or G3YWX/P, etc.
The data is encoded and the way in which it is done reduces the number of bits to be transmitted, but forward error correction is added to improve the robustness of the transmission.