v1.161: FSK/RTTY extension

edited January 2018 in KiwiSDR Discussion
v1.161 has an FSK extension. It needs a lot of work, but works okay on a number of signals. The framing "5N1V" means "variable number of stop bits" (but at least one). This is needed by stations like PBB (Dutch Navy) on 2474 that sends truly asynchronous bit streams.


  • where are the controls for FSK?
  • Looks like I forgot to enable it. It will be available in v1.161 later today..

  • Hi John,

    It works very well. apart from the extension box doesn't pop out when using my iPad (this has occurred previously with other extensions which are now working OK)

    I like the scope and bit displays they are very useful. I had already used the ones in the Navtex decoder to takes a look at some other FSK signals, but this new option is even better. I assume you will eventually roll the FSK and Navetx decoders into one extension ?

    Would it be possible to embed extension configurations into dx tags and the URL ? 

    This would be useful if you tune to a signal and want to decode it without knowing what type it is. Otherwise you have to open up the Fax, Navtex, FSK (and possibly other future modes) and then scroll through the frequency lists until you find one that may or may not match the frequency you are tuned to. 

    It would also be useful if it was possible to define the antenna to be used if the antenna switch extension is installed. For example being able to set a different antenna for tagged VLF stations.


    Martin - G8JNJ
  • edited January 2018
    I am also interested in the fsk extension, but at my Firefox (old) on my Snow Leopard, it also does not pop up. I am at version 1.161
  • jksjks
    edited January 2018
    Once again in my haste to meet the auto-update deadline I didn't get to test on iPad. Will be fixed in today's v1.162 update..

    Not clear Navtex and FSK should be a single extension. I am adding the specialty modes for EFR (Teleswitch signals at 130-140 kHz) and CHU to the FSK extension since they are just simple decode additions.

    I need to add FSK parameters to the ext=fsk,<params> part of the URL.

  • Hi John
    According EFR (Teleswitch signals) 
    You have 7N0V as framing.
    When I look in the papers it should be 8bit data + parity + 1 stop bit

    Bjarne Bachmann
  • jksjks
    edited January 2018
    Yes, my software for EFR is already way beyond what was in the v1.161 release. It took a while, but I finally found more details for not only the framing but the telegram formatting as well. Also, I have actually heard HGA22 and DCF39 (but not DCF49) here in New Zealand. It happens right at sunrise during certain times of the year (greyline propagation). This was from November 2016 (note 5:39 AM local time)


  • jksjks
    edited January 2018
    The v1.162 release has the special framing modes 'EFR' and 'EFR2' (and 'CHU' which is under development). For EFR the timestamp packets are decoded (most fields) because I found a reference describing the telegram format. Other telegrams are just printed as hex and ASCII dumps. EFR2 mode suppresses the display of the more common telegrams.

  • I was able to receive DDH 47 Weather station at it's 147,3 kHz from Frankfurt. Works well.
  • Release v1.163 adds time station CHU (Ottawa, Canada) decoding. It works, but is not very robust. The Bell 103 compatible format they transmit is not the best fit to the FSK demodulator we use.

  • CHU 3330 is loud most of the day here in Rochester NY, and the decode works well
  • Hi John,

    At some point would it be possible to add user defined shifts and baud rates ?

    Some of the more 'interesting' signals on this webpage are not currently configurable.


    Martin - G8JNJ
  • I started to add a "custom" entry to the menus that would bring up a field where you could enter a numeric value, but there were user interface complications. So I set that aside for now. If you have specific values you want added to the menus let me know. That's easy to do.

    That's a nice site. I've been looking for a good list of stations with detailed information. Not just shift/baud-rate but format as well to help me see if I might be able to add some automatic classification capability. This is the differentiating feature of advanced decoders. The way they can compute autocorrelation at the bit format and message format level to help determine the timing parameters.

  • Hi John,

    Yes it's a useful site when trying to ID signals (like the Signal ID Wiki).

    They also link to another Russian site with an interesting bit of signal analysis software which doesn't seem to have been updated for the past few years.

    Cost for a single licence is about £70 GBP which is a bit steep. However there is a demo version which can be used to analyse audio files.

    It may be worth taking a look at for some further ideas ?


    Martin - G8JNJ

  • Alright, that was easier to do than I thought. Custom (arbitrary) shift and baud rate fields in v1.165..

  • Hi John,

    Thanks for adding that feature, much appreciated.

    I find that it's still a bit difficult to identify the settings for unknown signals.

    The free version of signals analyser doesn't work that well, but the full version (without licence key) seems to still have the same (or better) functionality as the free version ?

    The full version http://signals.radioscanner.ru/info/files/item1/sa_6267.rar allows you to place cursors on the waveforms in order to determine the shift and bitrate of an unknown signal.

    Maybe it would be possible to add something like that to the extensions by placing cursors on an additional audio fft screen within the extension to set the shift, and then on the scope screen to set the bitrate.


    Martin - G8JNJ
  • In v1.166 I have added shift markers on a waterfall overlay. Only enabled when zoom >= 10.

    Because of the relatively low-Q mark/space filters used by the FSK software I'm using sometimes the actual shift value is not that critical. For example a strong DDK2 on 4583 (shift 450) can be decoded fine using shifts from 340 to 500. Probably a different story for weaker signals though.

    I found the Rivet Java/FFT-based decoder which should be useful (https://github.com/IanWraith/Rivet).

    I've been meaning to look at SA in more detail. Very advanced capability for much less than the 4-digit price tags of the professional decoders. Unfortunately it seems the author, Serg, is now an SK. Pity the code didn't go open source after that. I don't know who's selling it now.

  • Hi John,

    I like the new shift markers that makes things a lot easier :-)

    Would it be possible to stop it e-zooming to WF 12 when a new shift is selected ? Or alternatively zoom to WF 13 or 14  when very narrow shifts are selected ?

    Rivet looks to be very interesting - I'll enjoy playing with that :-)


    Martin - G8JNJ
  • Hi John,

    Quite a few 170Hz  / 100bd  FSK signals I've heard (but not decoded) turn out to be "Digital selective-calling system for use in the maritime mobile service" using a  ten-bit error-detecting code. 

    DSC calling frequencies

    • 2.1875 kHz
    • 4.2075 kHz
    • 6.312 kHz
    • 8.4145 kHz
    • 12.577 kHz
    • 16.8045 kHz

    Martin - G8JNJ

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