Also known as: FT8
FT8 is a weak-signal amateur-radio digital mode that completes minimal contacts — callsigns, grid locators, and signal reports — at signal levels well below what the ear can hear. It uses 8-ary FSK in tightly synchronized 15-second slots and an LDPC error-correcting code, so a decode can succeed at signal-to-noise ratios around −21 dB in a 2.5 kHz reference bandwidth.1 Named for its designers Franke and Taylor and its 8 tones, FT8 became the most popular mode on the amateur HF bands within a few years of its 2017 release.
Overview
An FT8 exchange is deliberately spartan. Stations alternate transmit and receive on 15-second boundaries locked to UTC, so accurate clock synchronization (usually via NTP) is essential. A full QSO — call, grid, signal report, roger-report, and 73 — takes about a minute. Because every station in a passband transmits in the same slots, a single receiver decodes dozens of overlapping signals at once across the audio spectrum.
Technical characteristics
| Property | Value |
|---|---|
| Modulation | 8-FSK, Gaussian-smoothed, 6.25 Hz tone spacing |
| Symbol rate | 6.25 baud (79 symbols per transmission) |
| Occupied bandwidth | ~50 Hz per signal |
| Slot length | 15 s (12.64 s of tones) |
| Message payload | 77 bits |
| FEC | LDPC(174,91) with 14-bit CRC |
| Sync | three 7×7 Costas arrays |
| Threshold | ≈ −21 dB SNR (2.5 kHz reference) |
History
FT8 was introduced in mid-2017 by Steven Franke (K9AN) and Nobel laureate Joe Taylor (K1JT) as part of the free WSJT-X software suite. It combined the sub-noise sensitivity of earlier modes like JT65 with a far faster 15-second cadence, and the modern LDPC code replaced the older Reed-Solomon approach. Its speed and sensitivity made it dominant on the HF bands almost immediately.2
Deployment
FT8 runs worldwide on the HF amateur bands (notably 20 m at 14.074 MHz) and on VHF/UHF for weak-signal work. Decodes are widely uploaded to spotting networks such as PSK Reporter, producing real-time global propagation maps. A faster sibling, FT4, uses 7.5-second slots for contesting.
Decoding it with GopherTrunk
GopherTrunk does not decode FT8 — it is a trunked-radio scanner focused on land-mobile systems (P25, DMR, NXDN, TETRA and similar), not HF weak-signal modes. FT8 is received with a general-coverage SSB receiver or SDR feeding audio into WSJT-X, the reference decoder, or compatible software such as JTDX. Any SDR that can deliver a clean 2–3 kHz USB audio slice on the right band and dial frequency, with an accurately set clock, is a suitable front end.
Sources
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FT8 — Wikipedia, for the 8-FSK air interface, 15-second timing, LDPC coding, and the mode’s origin and popularity. ↩
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The FT4 and FT8 Communication Protocols — Franke, Somerville & Taylor, QEX, the authoritative description of the FT8 waveform, message format, and coding. ↩