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Very weird "glitching" while TX'ing via FT8 !!??

Mike - K6QYMike - K6QY Member ✭✭

Rig: Flex 6400
OS: Windows 10 Pro - 64-bit (fully updated to current release/updates) 
SSDR: Latest

I've been having this problem intermittently for a while. When I start an FT8 transmission, everything looks great (see spectrum on left). Then, quasi-randomly, the system glitches and the output goes nuts (image at right; same vertical scale as on left). Lots of wide-bandwidth spurious stuff appears, clearly visible in both the waterfall and spectrum display.

Previously, I had been able to circumvent this by shutting the system down and doing a cold boot (removing connection to power). Now, it no longer seems to fix things.

First thing I explore was changing the DAX "TX Gain". (It occurs irrespective of whether I'm at a very low modulation level, or up at standard levels... which for me is a setting of about "40" and TX level stays between -10dB and 0dB.

Other things I've tried (all unsuccessfully):
1. Shutting down, removing power. Restarting.
2. Completely reloading both SSDR and WSJT-X. (What a pain. No gain...)
3. Tried both previous release SSDR v3.0.27 and current v3.1.8

N.B. SWR is always << 1.2 : 1

System can go for days FB, with absolutely no problem. Then, spontaneously, it decides to act up in this bizarre way.

Could this be a hardware problem?

Thanks for any and all suggestions...


  • Pat N6PATPat N6PAT Member ✭✭
    edited October 2019

    You problem is similar to an issue I'm having which I posted about the other day. Look at the video and see how crazy my 6700 goes. it's done  it at least twice now. Running v2.6.1 Windows 10 1803

  • Bob G   W1GLVBob G W1GLV Member ✭✭
    edited June 16
    Mike, the problem is with DAX, if you stop it and restart it, it goes away.
  • Pat N6PATPat N6PAT Member ✭✭
    edited October 2019
    In my case I had to reset the radio back to factory specs. Nothing else would work including rebooting both the radio and computer.
  • Mike - K6QYMike - K6QY Member ✭✭
    edited December 2019
    So, I've done the hard reset (hold button for 5s while powering up, until it turns white). This fixed the problem. But for how long? There seems to be an instability in the system...
    Thoughts, anyone?

    (Thanks to Pat, & 73)
  • Mike - K6QYMike - K6QY Member ✭✭
    edited October 2019
    ... now let me see if I can recover all of my profiles. Aargh, didn't follow the old maxim: "always be sure you're backed up!"
  • Mike - K6QYMike - K6QY Member ✭✭
    edited December 2019
    Folks... I spoke too soon. The hard reset did NOT fix the problem. It reappeared after about a minute.
  • John - AI4FRJohn - AI4FR Member ✭✭
    edited October 2019
    When I first got my 6700 about 2 years ago it would at times do something very similar to what you are seeing Mike. I thought great, this used radio I just bought has issues. My next thought was to operate the radio from another PC. I had no issues. Then a short while later I lost a hard drive in the main PC so I did a fresh install of everything and bingo it's been clean since. That was about a year and a half ago.

    In my case, shutting down DAX and restarting it solved the problem as well. No always, but most of the time.

    Good luck with it.
  • Bill NE1BBill NE1B Member ✭✭
    edited October 2019
    This is the standard "DAX distortion" issue which was supposedly corrected in V3.1.7.  It will vary with computer DAXing between WSJT-X app and Flex app.
  • Mike - K6QYMike - K6QY Member ✭✭
    edited December 2019
    Hmm. I guess it continues “un-fixed” then on into v3.1.8. I’ll send in a help ticket to flexradio.
  • Mike - K6QYMike - K6QY Member ✭✭
    edited October 2019
    Hi Bob: Thanks. Each time I reboot DAX starts anew. So, there seems to be something more pernicious going on.
  • Mike - K6QYMike - K6QY Member ✭✭
    edited December 2019
    Folks, with the kind help of Flex support my problem is now identified (but not yet fixed). The glitching is due to intolerable latencies in my Windows 10 platform, aka "":

    From Flex Support:
    - - - - - - - - - - - - - - -

    Ken Wells (FlexRadio Systems) 

    Oct 16, 3:58 PM CDT

    Hello Michael,

    Some stations seem to have more troubles with DAX Buffer Corruption than others.
    The issue has multiple causes, but a major contributor is DPC's (Deferred Procedure Calls) on your computer.

    Here are two articles that Tim has written that can help explain some things.




    Computers that do not have many log duration DPC's seem to have little problem with the DAX Buffer Corruption issue.  Those with lots of DPC's will have them on a very frequent basis.

    Why is this a problem for DAX but not for Youtube, Netflix, and other streaming services?
    Because with FlexRadio and DAX we are dealing with live, real-time, digital audio where precise timing is critical to the correct function of the system.  Youtube, Netflix, IP Phones, and other streaming services in general do not require the precision and timing required for what DAX is doing.

    Please read these articles and see if this may be part of your difficulty.

    Ken Wells, NM9P

    FlexRadio Systems™
    4616 W Howard Ln Suite 1-150

    Austin, TX 78728
    - - - - - - - - - - - - - - - -

    Having now installed and run the app during both FT8 RX and TX protocols, I find that the DPCs are only of order a few hundred microsecs for RX, but can approach 15 millisecs for TX.  Yikes!!  Apparently, problems arise when such latency rises to only about 1mS = 1000uS. I only have SSDR 3.1.8 and WSJT-X (latest) running. So, I'll have to dig into this further. FYI, my screen shot of the results from LatencyMon are shown below.

    If anyone has useful suggestions... I'm all ears!  73's.

  • Dudley  WA5QPZDudley WA5QPZ Member ✭✭
    edited March 21
    Mike, DPC latencies can come from many places, bad or wrong drivers, software issues, BIOS not updated or incorrect settings, just to name a few. It appears you are running VMWare , unless tuned correctly this can cause an issue. Try stopping VM Ware , try again. Also make sure you go to you sound card , LAN and video vendors , get the current driver for you sound , LAN, and video devices . 73, Dudley

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