W1JT, author of weak signal communications software such as WSPR, announced in late October a new data mode for 136 and 477/500kHz operation. WSJT-X uses multi-tone FSK and therefore does not need a linear transmitter. It does, however, require a way of converting audio to 136 or 477/500kHz RF, for instance an SSB transmitter capable of generating RF at this frequency or via a transverter from HF to LF. More information is available from here, together with how to download the free software.
Like WSPR it can be used in SWL mode (only a receiver and soundcard are needed), though as the software is experimental it does not yet include internet reporting. The main difference with WSPR or Opera modes is that it allows real two-way contacts to take place, exchanging whatever information you want in small bursts.
Several speeds (sub-modes) are currently available: WSJT9-1 has one-minute long transmissions, WSJT9-2 two seconds and so on with five, ten and thirty second sub-modes installed. To decode a station, the transmit ands receive stations must be switched to the same sub-mode. The longer-duration sub-modes contain the same amount of data, but can be received at lower signal-noise levels.
WSJT-X is in the early stages of development so it has a few rough edges, but it has the capability of being the new two-way weak signal mode on the 136 and 477/500kHz bands.
