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WSPR - weak signal beaconing

What is WSPR?

This is best described by quoting verbatim from 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.

As of early January 2013 there is now a new version called WSPRX which also supports a slower, even more sensitive, version called 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.
The screen with the waterfall like display shows the received WSPR signals (2 minutes long for WSPR2) and those successfully decoded, together with relevant data for each station logged. On the 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!

Stand-alone WSPR beacons

A number of people have now built stand-alone WSPR beacons using PICs or similar microcontrollers to generate the WSPR code.  All need a way of getting accurate timing so that the WSPR burst begins precisely at the right time. This can be done manually if the time is known accurately, but more usually with a GPS derived timing signal. Several kits are now available that include the WSPR generator with pre-programmed user callsign and QTH locator together with a QRP transmitter.


DX Potential

Worldwide reception of even very low powered (mW or even uW level) WSPR modulated transmitters is possible on most HF bands. In fact to use more than a few watts with WSPR is considered downright antisocial! Most users find that 1-5W is perfectly fine and many enjoy doing tests at much lower levels. Recently I saw one station was testing with just 1uW and STILL getting spots on an HF band.

WSPR2 Frequencies

WSPR15 uses the same USB dial frequencies but place the TX frequencies in a band 25Hz above the 200Hz wide band used for WSPR2.

 BANDUSB Dial Frequency
 Actual TX frequencies
 33400m 7.200kHz 8.700 - 8.900
 2200m 136.00 137.40-137.60
 630m 474.20 475.70-475.80
 160m 1.8366MHz 1.8380 - 1.8382
 80m 3.5926  3.5940 - 3.5942
 60m 5.2872 5.2886 - 5.2888
 40m 7.0386 7.0400 - 7.0402
 30m 10.1387 10.1401 - 10.1403
 20m 14.0956 14.0970 - 14.0972
 17m 18.1046 18.1060 - 18.1062
 15m 21.0946 21.0960 - 21.0962
 12m 24.9246 24.9260 - 24.9262
 10m 28.1246 28.1260 - 28.1262
 6m 50.2930 50.2944 - 50.2946
 4m 70.0910 70.1310-70.1510
 2m 144.4885 144.4899 - 144.4901

Where to get WSPR Software?

Download WSPR software for Windows free at K1JT's WSPR download site .

About Joe Taylor, K1JT

Joe Taylor wrote the software for WSPR. He is a very clever and, by all accounts, very decent person too, I see he is a Quaker.  He is also a Nobel Prize winning physicist for his work on astronomy and relativity. Details about Joe and his distinguished career may be found at http://en.wikipedia.org/wiki/Joseph_Hooton_Taylor,_Jr.