Technical

New FT8 Mode included in WSJT-X Beta Release

WSJT-X version 1.8.0 includes a new mode named FT8

This mode features:

  • QSOs 4 times faster than JT65 or JT9
  • Sensitivity down to -20 dB on the AWGN channel
  • Auto-sequencing includes an option to respond automatically to first decoded reply to your CQ

WSJT-X source code; along with installation packages for Windows, Linux, OS X, and Raspbian; is available for download at http://physics.princeton.edu/pulsar/K1JT/wsjtx.html

About the FT8 protocol

WSJT-X Version 1.8.0 includes a new mode called FT8, developed by K9AN and K1JT. The mode name “FT8” stands for “Franke and Taylor, 8-FSK modulation”. FT8 uses 15-second T/R sequences, provides 50% or better decoding probability down to -20 dB on an AWGN channel, and maintains good performance on Doppler-spread fading channels. An auto-sequencing facility includes an option to respond automatically to the first decoded reply to your CQ. FT8 QSOs are 4 times faster than those made with JT65 or JT9. FT8 is an excellent mode for HF DXing and for situations like multi-hop E_s on 6 meters, where deep QSB may make fast and reliable completion of QSOs desirable. [ 1 ]

Some 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, tone spacing 6.25 Hz
  • Constant-envelope waveform
  • Occupied bandwidth: 50 Hz
  • Synchronization: 7x7 Costas arrays at start, middle, and end
  • Transmission duration: 12.64 s
  • Decoding threshold: -20 dB; several dB lower with AP decoding
  • Multi-decoder finds and decodes all FT8 signals in passband
  • Optional auto-sequencing and auto-reply to a CQ response
  • Operational behavior similar to JT9, JT65

Footnotes

[ 1 ] “WSJT-X Release Notes”, Joe Taylor K1JT, retrieved July 18 2017, https://physics.princeton.edu/pulsar/k1jt/Release_Notes_1.8.0.txt.