Version 2.3 of WSJT-X introduces new modes, collectively referred to as FST4. Compared to other modes used so far, they achieve better properties that approach the theoretical limits of the transmission capacity. They use 4-GFSK modulation with different lengths of T/R sequences of 15, 30, 60, 120, 300, 900 and 1800 seconds. Submodes A, B, C and D have different pitches. This increases their effectiveness in different propagation and Doppler effect conditions. In principle, FST4 digital modulation should be usable on wavelengths from 2200m to 23cm inclusive EME connections. Do not confuse FST4 with FT4.
FST4W-120A, -300A, -900A, -1800A as WSPR beacon broadcasting for bands 630 and 2200 m
FST4-120A, -300A, ... for connections on 630 and 2200 m bands
FST4-15A for connections by reflection from the ionosphere at 50 MHz
FST4-15A, -30B, -30C, -30D rýchle (contestové?) EME QSO on 144 – 1296 MHz?
FST4-120B, -120C, -300C, -300D EME on 50, 144, 432 MHz with the possibility of detecting weak signals
What are the FST4 options?
| T/R period (with) | Symbol length (with) | Pitch (Hz) | Occupied width (Hz) | FST4 SNR (dB) | FST4W SNR (dB) |
| 15 | 0.060 | 17, | 68, | -21, | -22, |
| 30 | 0.140 | 7, | 29, | -24, | -26, |
| 60 | 0.324 | 3, | 12, | -28.0 | -30, |
| 120 | 0.683 | 1, | 6, | -31, | -33, |
| 300 | 2, | 0.56 | 2, | -35, | -37, |
| 900 | 6, | 0.180 | 0.72 | -40, | -42, |
| 1800 | 11,200 | 0.089 | 0.36 | -43, | -45, |
How to get started with FST4 can be found in the manual https://jl1jvt.cocolog-nifty.com/blog/files/fst4_quick_start.pdf More information about WSJT-X you can find at https://physics.princeton.edu/pulsar/K1JT/wsjtx.html