It’s still in beta testing, but FT8 — the latest digital bauble to capture the imagination of the Amateur Radio community — has been luring away many of those already using the popular JT65 “weak-signal” mode. FT8 is included in a beta release of WSJT-X, version 1.8.0-rc1. Among its biggest advantages is a shorter transmit-receive cycle, meaning quicker contacts. The notes for the “candidate” release say that FT8 offers “sensitivity down to –20 dB on the AWGN channel.” Contacts are four times faster than with JT65 or JT9, and an entire FT8 contact can take place in about 1 minute.
The new mode is named after its developers, Steven Franke, K9AN, and Joe Taylor, K1JT. The numeral designates the mode’s 8-frequency shift keying format. Tones are spaced at 6.25 Hz, and an FT8 signal occupies just 50 Hz. Unlike JT65 or JT9, transmit and receive cycles in FT8 each last about 15 seconds. Like JT65, FT8 requires accurate time synchronization. An auto-sequencing feature offers the option to respond automatically to the first decoded reply to your CQ.
“FT8 is an excellent mode for HF DXing and for situations like multi-hop Es on 6 meters, where deep QSB may make fast and reliable completion of QSOs desirable,” Taylor’s release notes assert.
The beta release came out just days before the July CQ VHF Contest and proved to be a boon to many operators who took advantage of FT8 on 6 meters. In a limited outing for the CQ VHF, Frank Donovan, W3LPL, made 22 FT8 contacts on 6 meters, “during which the FT8 software reported SNRs from my receiver below –10 dB (measured in a 2,500-Hz bandwidth). Some of the 22 QSOs may have been difficult to complete on CW.”
Enthusiasts will have to wait a little longer for Logbook of The World (LoTW) to accept FT8 contacts as FT8 contacts. Because FT8 is still in beta, it has not yet been added to the ADIF tables. Configuring TQSL to automatically map FT8 contacts to “DATA” will enable users to upload FT8 contacts now, and confirmations will be valid for DXCC Digital, VUCC, WAS Digital, and WPX Digital awards. A new TQSL configuration will be released once the new mode has been accepted to ADIF, which could happen within a week.
Operational documentation for FT8 has not yet been finalized. “We know that the advent of new mode FT8 means that new material is needed for the User Guide,” Taylor told the Yahoo Meteor Scatter and Weak Signal Group this week. “We will be working on that in the near future.”
From ARRL
Joe Taylor, K1JT, announced on June 29, 2017 the availability of a new mode in the WSJT-X software, FT8. FT8 stands for “Franke-Taylor design, 8-FSK modulation” and was created by Joe Taylor, K1JT and Steve Franke, K9AN. It is described as being designed for “multi-hop Es where signals may be weak and fading, openings may be short, and you want fast completion of reliable, confirmable QSO’s”.
According to J. Taylor, the important characteristics of FT8 are:
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 = 6.25 Hz
Waveform: Continuous phase, constant envelope
Occupied bandwidth: 50 Hz
Synchronization: three 7×7 Costas arrays (start, middle, end of Tx)
Transmission duration: 79*1920/12000 = 12.64 s
Decoding threshold: -20 dB (perhaps -24 dB with a priori 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
Compared to the so called 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. Compared with the 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. Features not yet implemented include signal subtraction, two-pass decoding, and use of a priori (already known) information as it accumulates during a QSO.”
From WSJT