Welcome to the new FlexRadio Community! Please review the new Community Rules and other important new Community information on the Message Board.
If you are having a problem, please refer to the product documentation or check the Help Center for known solutions.
Need technical support from FlexRadio? It's as simple as Creating a HelpDesk ticket.

FSK Support?

Jerry Gardner
Jerry Gardner Member
edited February 2019 in SmartSDR for Windows
What are the plans for supporting FSK on the Flex-6000 series? It seems to me that this should be easy to implement.


  • Jim Gilliam
    Jim Gilliam Member ✭✭
    edited April 2016

    Have you tried fldigi? The CAT interfaces very nicely and you will have just about all the digital modes.

  • Doug Hall
    Doug Hall Member ✭✭
    edited February 2019
    I was always a huge FSK enthusiast, and was initially disappointed when I found that it wasn't supported in the Flex with SmartSDR. But Tim is correct. Ever since Flex added the RTTY enhancements to SmartSDR (back in version 1.5, I believe) running AFSK with DAX provides performance that is as good as any rig I've ever owned that had hardware FSK.

    For some legacy rigs there is a good technical reason to use FSK RTTY - on some rigs you can only select the narrow IF filters for RTTY if you are using FSK. But that's not an issue with the Flex.

    One issue with FSK is how the FSK signal is actually generated by the digital mode software. For sound card modems it pretty much requires a serial port. Honest-to-goodness COM ports are going away, and as time goes on there will likely be fewer and fewer USB-to-Serial adapters that support 45.45 baud operation. And none of the old standalone boxes (AEA, Kantronics, etc.) provide the performance of PC sound card modems. My HAL, IRL, AEA, Kantronics, and homebrew TUs have been gathering dust for years.

    Bottom line (for me) is that I won't bother switching to FSK if/when Flex adds support for it. Can't see any reason to. And this is from a guy who wrote an article for QST in 2011 promoting the use of FSK.

    Doug K4DSP

  • DH2ID
    DH2ID Member ✭✭✭
    edited December 2016
    I fully concur with you about how FSK works, Doug.

    Programming it into firmware should be fairly easy, as the SDR only has to
    generate mark and space tones which are triggered by either an internal setup
    analogue to CWX or an external software program.

    The main advantage of FSK over AFSK has always been that the tones for
    AFSK are always triggered by an external program and then generated by
    either the internal PC/notebook soundcard, which could be susceptible to
    tone frequency drift or an external soundcard. I have always relied on
    external soundcards as I worked a lot of SSTV and FAX and anybody who
    does this knows about slant correction... There is also a very small time delay
    before the tones arrive in the TRX and are transmitted or decoded and there
    always has been the Windows latency problem. All this is eliminated by
    FSK, but do we still need FSK in a modern SDR TRX?

    My FSK setup: IC-756PRO set to RTTY or TS-2000X set to FSK
    - microHAM DigiKeyerII interface - HamRadio Deluxe DM780 in FSK mode.
    This works very well and the IC-756PRO even has a dedicated RTTY filter
    for FSK. But testing and working under all condx did not show a significant
    difference between FSK and AFSK, which I can also work with this setup.

    My AFSK setup: Flex6k5 set to RTTY and HamRadio Deluxe DM780 in AFSK
    mode. This setup works equally well and I see no difference in character
    recognition and behaviour in QSB situations.

    73, Alex - DH2ID

  • Jerry Gardner
    Jerry Gardner Member
    edited April 2016
    What is the trick to getting RTTY to decode in DM780 with the Flex set to RTTY mode? It doesn't work for me unless I set the rig to DIGU or USB.
  • George KF2T
    George KF2T Member ✭✭✭
    edited December 2016
    RTTY mode in SSDR is a narrow LSB. If your software allows, try using "reverse" tones.

Leave a Comment

Rich Text Editor. To edit a paragraph's style, hit tab to get to the paragraph menu. From there you will be able to pick one style. Nothing defaults to paragraph. An inline formatting menu will show up when you select text. Hit tab to get into that menu. Some elements, such as rich link embeds, images, loading indicators, and error messages may get inserted into the editor. You may navigate to these using the arrow keys inside of the editor and delete them with the delete or backspace key.