- Written by G Wolfe - KI0KK
Steve (K9AN) and I (Joe - KIJT) have developed a potential new mode for WSJT-X. We’re
calling the mode “FT8” (Franke-Taylor design, 8-FSK modulation).
FT8 is designed for situations like multi-hop Es where signals may be
weak and fading, openings may be short, and you want fast completion of
reliable, confirmable QSOs.
Note: This mode has gained wide acceptance since it's introduction as a replacement for JT-65.
Important characteristics of FT8:
– T/R sequence length: 15 s
– Message length: 75 bits + 12-bit CRC
– FEC code: LDPC(174,87)
– Modulation: 8-FSK, keying rate = tone spacing = 5.86 Hz
– Waveform: Continuous phase, constant envelope
– Occupied bandwidth: 47 Hz
– Synchronization: three 7×7 Costas arrays (start, middle, end of Tx)
– Transmission duration: 79*2048/12000 = 13.48 s
– Decoding threshold: -20 dB (perhaps -24 dB with AP decoding, TBD)
– Operational behavior: similar to HF usage of JT9, JT65
– Multi-decoder: finds and decodes all FT8 signals in passband
– Auto-sequencing after manual start of QSO
*Comparison with slow modes JT9, JT65, QRA64:* FT8 is a few dB less
sensitive but allows completion of QSOs four times faster. Bandwidth is
greater than JT9, but about 1/4 of JT65A and less than 1/2 QRA64.
*Comparison with fast modes JT9E-H:* FT8 is significantly more
sensitive, has much smaller bandwidth, uses the vertical waterfall, and
offers multi-decoding over the full displayed passband.
*Still to come, not yet implemented:* We plan to implement signal
subtraction, two-pass decoding, and use of “a priori” (already known)
information as it accumulates during a QSO.
Three extra bits are available in the message payload, with uses yet to
be defined. We have in mind special message formats that might be used
in contests, and the like. Your considered suggestions for use of these
bits are very welcome!
[Text by Joe Taylor - K1JT]
Digital Mode Software
- Written by Administrator
There are several sources of software to operate digital modes, both free and paid. This artilce list several of the most common software packages in use at this time. Seveal of theses packages also provide rig and rotor control. Some of the modes such as JT-65, JT-9 and FT-8 use software that only supports these specific modes.