Whats the trick to decoding FSK?

smgsmg
in Signals Received

There are a few of these, which I believe I have identified as FSK.

image.png

However, there are a lot of variables, and stabbing in the dark is a PITA. :-)

Comments

  • jksjks

    I wish I could find some open source code that does FSK signal parameter classification (and digital classification in general). But software like that tends to be proprietary and cost money (and for good reason).

    Under the "decode" menu are two modes "scope" and "framing" that I used during development to help classify unknown signals to establish their parameters. But they are tricky to use and are not documented anywhere.

    smg
  • G8JNJG8JNJ

    You will have difficulty decoding anything from that signal, it is US Navy, 850Hz shift 50bd KW-46 Encrypted, Lualualei, Hawaii.

    Try using some of the KiWi's preset stations in the FSK extension, to get a better "feel" for the different shifts and baud rates.

    The most common FSK signals tend to be Russian 200Hz (or near) shift "BEE" format.

    https://www.sigidwiki.com/wiki/CIS-36-50

    https://www.sigidwiki.com/wiki/CIS-50-50

    Regards,

    Martin

    smg
  • smgsmg

    Ah good to know thanks both!


    Ill keep beavering away. I got some gibberish from a signal the other night then after about 30 mins, gave up making sense of it. :-)

  • bensonbenson
    edited August 27

    You could also have a look at Rivet (https://github.com/IanWraith/Rivet/wiki/Introduction). This is an open source decoder written in java that can work with kiwi wav recordings or directly from the audio when using a virtual soundcard. The Rivet code does not do automatic classification however.

    It looked quite promising as a FSK type of signal decoder with features as automatic speed and shift adjustment, but it appears the development has stopped unfortunately.

    What you will find is that some of those signals such as CIS36-50 (BEE) can indeeed be decoded with it, but as expected seldom deciphered. Those that are in plain text (NAVTEX, DSC, MSI, FSK meteo) can already be explored with the existing Kiwi extensions.

    brgds, Ben

    smg
  • smgsmg

    Seems rivet is long abandoned and the binaries are no longer available and only 12yr old source code is there :-/

  • bensonbenson
    edited August 28

    Well, not really abandoned as you can see in this post from April this year: https://priyom.org/blog/priyom-releases-rivet-build-91

    smg
  • smgsmg

    Ah nice. its being maintained by priyom!

  • KenAlexanderKenAlexander

    I'm decoding an FSK signal as I write this. It appears to be from Uruguay and has information on traffic and weather around the Rio de la Plata, the major river there. Good signal considering they're in Uruguay and I'm in northgeast Thailand.

    1030 UTC

    8416.54 kHz

    It started decoding with the Kiwi's default FSK decoder settings. Will report more as I find them.

    Best advice is just to pull up the Weather and Marine frequency lists and cycle through the frequencies, staying no more than a few seconds on each one.

    73,

    Ken VE3HLS

    So Phisai, Thailand OK18sc

    smg
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