At present WSPR is a stand-alone executable, independent of WSJT. It is functional for both transmitting and receiving, but it has no frills -- no graphics, no GUI, etc. It is executed from a Windows command prompt. Like WSJT, 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. Basic operating instructions for the initial release can be found in the file at WSPR_Instructions.TXT , and the program itself can be downloaded.

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 exactly the same as the transmitted message, or else they are left blank.