WSPR
| WSPR | |
|---|---|
| Stands for | Weak Signal Propagation Reporter |
| Pronounced | "Whisper" |
| Developed by | Joe Taylor, K1JT |
| Software | WSJT-X (free); also stand-alone beacon transmitters |
| Technical | |
| Transmission | About 110 seconds, starting on even UTC minutes |
| Signal bandwidth | About 6 Hz |
| Message | Call sign, four-character grid square, power in dBm |
| Typical power | Milliwatts to a few watts |
| Network | |
| Reports go to | WSPRnet |
| 20 m dial frequency | 14.0956 MHz, upper sideband |
WSPR (pronounced "whisper"), the Weak Signal Propagation Reporter, is a digital beacon mode for finding out where a signal can be heard. Stations take turns transmitting a very slow, narrow signal carrying only a call sign, a grid square and the transmitter power, and listening for others. Every station that decodes a WSPR signal uploads a report to the internet, where it appears on a public map within minutes. With many stations taking part around the world, WSPR works as a live network for measuring propagation. It was created by Joe Taylor, K1JT, the Nobel Prize-winning physicist who also co-developed FT8, and was first released in 2008.
WSPR doesn't make contacts. It is one-way: a station transmits, other stations report hearing it, and nothing is exchanged between them on the air.
How it works
A WSPR transmission lasts just under two minutes, about 110.6 seconds, and begins one second after the start of an even-numbered minute of UTC. In that time it sends only 50 bits of information, protected by strong error correction, as four audio tones less than 1.5 Hz apart, giving a signal about 6 Hz wide. Because the message is so short and sent so slowly, the receiving software can pull it out of noise far too deep to hear, decoding signals even weaker than FT8 can manage. That is why a beacon running a fraction of a watt is often reported thousands of miles away.
The message has three parts: the call sign, a four-character grid locator, and the power in dBm (decibels relative to one milliwatt), so 30 dBm is 1 watt, 37 dBm is about 5 watts and 23 dBm is about 200 milliwatts. Receiving stations add the frequency, the signal-to-noise ratio and any frequency drift. A WSPR transmitter needs to be stable, since a signal that wanders by a few hertz over two minutes decodes poorly, and both stations need clocks accurate to about a second.
Stations spend most of their time listening. WSJT-X lets each user choose what percentage of the two-minute periods to transmit in, and it picks the transmit periods at random so that two stations don't keep transmitting at the same time and missing each other. For the low-frequency bands, WSJT-X also offers FST4W, a related mode that offers longer transmission periods for even greater sensitivity.
WSPRnet
Decoded reports, called spots, are uploaded automatically to WSPRnet (wsprnet.org), a public database and map. Each spot records who heard whom, on what band, at what time, how strongly and over what distance. A station that has been transmitting can look up its call sign and see every station that heard it, plotted on a map with lines showing the paths. Other websites present the same data as tables and charts, and the long archive of spots has been used in research on the ionosphere and the solar cycle.
Uses
- Checking a band. The map shows which paths are open right now from the station's own location.
- Comparing antennas. Running WSPR on one antenna and then another shows differences that are hard to judge from casual contacts, though propagation changes from minute to minute, so fair comparisons take care and many hours of data.
- Low-power experiments. Hams transmit with a few milliwatts, sometimes less, to see how far the signal goes.
- Receive-only reporting. Listening stations are just as useful to the network as transmitting ones. Some software-defined radios can decode several bands at once.
- Tracking balloons. Small, solar-powered "pico balloons" carry tiny WSPR transmitters that encode their position and altitude, and some have circled the globe several times.
Frequencies
WSPR uses a 200 Hz-wide window on each band. With the radio in upper sideband on the standard dial frequency, the window falls 1,400 to 1,600 Hz above the dial, and each station transmits at its own spot within it. Dial frequencies for the most active HF bands:
| Band | Dial frequency (USB) |
|---|---|
| 40 m | 7.0386 MHz |
| 30 m | 10.1387 MHz |
| 20 m | 14.0956 MHz |
| 17 m | 18.1046 MHz |
| 15 m | 21.0946 MHz |
| 10 m | 28.1246 MHz |
WSJT-X includes the standard frequencies for the other bands. Twenty and forty meters are among the busiest and are good places to start.