Sunday, December 30, 2012

JT9 - a new digital mode for the MF and LF AR gang

There is a new weak signal mode in town and if you are a MF/LW amateur radio operator, you are going to like it. This new 9-FSK digital communications mode (for 2-way QSOs) called JT9 is optimised for MF and LF bands.

JT9 uses the structured messages introduced in 2003 for the JT65 mode, now widely used for EME and for QRP operations at HF. JT9 can operate at signal levels as low as -27 dB (in a 2500 Hz reference bandwidth), with one-minute timed transmissions. It also offers slower transmissions of 2, 5, 10 and 30 minutes duration, and the slowest mode can decode signals as weak as -40 dB. With one-minute transmissions, submode JT9-1 has a total bandwidth of just 15.6 Hz -- less than one-tenth the bandwidth of a JT65A signal. The other submodes are narrower still: a JT9-30 signal occupies about 0.4 Hz total bandwidth.

Note that these JT9 sensitivity levels are comparable to or better than those of WSPR, which uses simpler messages and is not intended for making 2-way QSOs. JT9 has much higher throughput and reliability than QRSS CW, including DFCW modes.

JT9 is implemented in an experimental version of WSJT called WSJT-X. Some further details can be found at , and an early version of WSJT-X can be downloaded from

WSJT-X is in an early development stage. A number of improvements and enhancements are already in the works, and others will surely be added. 

Screen capture of 160 meter JT9 signals courtesy of PC4T