WSPR, which stands for Weak Signal Propagation Reporter, is a program used to test the propagation paths of RF signals between amateur radio operators using a narrowband digital transmission protocol called MEPT_JT on the HF and MF frequency bands. WSPR uses a computer sound card to generate audio tones to modulate an SSB transceiver operating on upper sideband. In receive mode the sound card digitizes audio from the transceiver. The program scans a 200 Hz passband (the "QRSS window") looking for MEPT_JT signals and decodes them. When the signal is received and successfully decoded the program uploads the decoded message to the WSPR database along with the location of the receiver so that the propagation path of the signal can be recorded and visualized. Basic operating instructions for the initial release can be found in the WSJT-X User Manual, and the program is available under the WSJT-X software which can be downloaded here.

Basic specifications of the MEPT_JT mode are as follows:

1. Transmitted message: callsign + 4-character-locator + dBm Example: "K1JT FN20 30"

2. Message length after lossless compression: 28 bits for callsign, 15 for locator, 7 for power level ==> 50 bits total.

3. Forward error correction (FEC): long-constraint convolutional code, K=32, r=1/2.

4. Number of channel symbols: nsym = (50+K-1)*2 = 162.

5. Keying rate: 12000/8192 = 1.46 baud.

6. Modulation: continuous phase 4-FSK. Tone separation 1.46 Hz.

7. Synchronization: 162-bit pseudo-random sync vector.

8. Data structure: each channel symbol conveys one sync bit and one data bit.

9. Duration of transmission: 162*8192/12000 = 110.6 s.

10. Transmissions start two seconds into an even UTC minute: i.e., at hh:00:02, hh:02:02, ...

11. Occupied bandwidth: about 6 Hz

12. Minimum S/N for reception: around -27 dB on the WSJT scale (2500 Hz reference bandwidth).

You can run Argo, Spectran, or WSJT at the same time as WSPR, in order to provide a waterfall spectral display.

In normal operation WSPR displays information every two minutes and is silent otherwise. In transmit mode in prints a single line when a new transmission starts. In receive mode the program looks for all detectable MEPT_JT signals in a 200 Hz passband, decodes them, and displays the results. If nothing is decoded, nothing will be printed. In T/R mode the program alternates in a randomized way between transmit and receive sequences.

Like JT65, MEPT_JT includes very efficient data compression and strong forward error correction. Received messages are nearly always the same as the transmitted message, or else they are left blank.