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FT8: New JT Mode for fast QSOs

Discussion in 'General Ham Radio Discussion' started by Moleculo, Jul 11, 2017.

  1. Moleculo

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    Staff Member

    Apr 14, 2002
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    This is a message from the founders of WSJT about a new experimental weak signal mode to have fun with:

    Steve (K9AN) and I 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.


    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 7x7 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!
    K1JT, K9AN, and G4WJS have conducted on-the-air tests of FT8 with excellent results. We're now at a stage where tests under a wider range of conditions are desirable. If you can build WSJT-X from source code revision r7750 or later, and would like to help, please do so and report your results to us! Pre-built installation packages will be made available after further testing is completed. Suggestions for FT8 setup can be found in the attached screen shot (above)
    We look forward to receiving your feedback.
    -- 73, Joe, K1JT

    Joe Taylor followed up with this note about frequencies for testeing:

    It will help to have some initial frequency coordination among those testing the new FT8 mode in WSJT-X v1.7.1.
    To help get things started, we suggest using the following frequencies:
    Band MHz
    160 1.841
    80 3.579
    40 7.079
    30 10.141
    20 14.079
    17 18.105
    15 21.079
    12 24.920
    10 28.079
    6 50.313
    4 70.094
    Most of these suggestions follow a simple guideline: add 3 kHz to the commonly used JT65 dial frequency.
    For 6 meters we suggest using 50.313, which should be consistent with band plans in all IARU Regions. (Six meter activity that's now on 50.276, world-wide, might be moved to 50.310.)
    We are very much open to suggestions for changes in the above table.
    -- 73, Joe, K1JT


  2. fourstringburn

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    W9WDX Amateur Radio Club Member K5KNM

    Feb 11, 2007
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    I do like to occasionally play on JT-65A so be sure to post when this new mode is available for downloading.
  3. Road Squawker

    Road Squawker
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    Sr. Member

    Jan 19, 2011
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    Well,I do a lot of 6 m JT65, it seems that "certain" people are starting to spread out so as to not create any QRM to other "pingJockey" users.
    Where did they get the idea that they should EACH get their own freq???
    Breaking news,..... QRM HAPPENS, and no, that is not illegal.

    You should watch them whine and moan on certain chatrooms as they complain about someone being in their passband or on "their" odd/even sequence. "I'm listening to Europe and that !@#$ with the wa4 call is TXing while I am listening" type comments.

    they are now going as low as 50.250, and Joe wants to go as high as 50.313?????????????

    Anyway, bearing that in mind,there is no need to "roll your own version" of FT-8, the autoextracting program is at https://physics.princeton.edu/pulsar/k1jt/wsjtx-1.8.0-rc1-win32.exe
    #3 Road Squawker, Jul 12, 2017
    Last edited: Jul 12, 2017
: JT8

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