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DAX Distortion - JT Transmit V1.5 (UNresolved)

rich Member
edited December 2018 in SmartSDR for Windows

Using 6300 for > 1 year on JTmodes.  Upgraded SDR to V1.5.  Still have intermittent problems with distorted transmit  - same exact symptoms as several others have posted in a thread started ~4 months ago (TITLE=DAX Distortion).  Photo included.



DISTORTED different band:


NORMAL transmit here (after rebooting FLEX):


Fellow JT operators are complaining about the distorted signal; some stations can decode, but most cannot.

Rich, K3VAT


  • DH2ID
    DH2ID Member ✭✭✭
    edited March 2017
    Try DIGU, not USB. You could otherwise have the equalizer and/or comressor in your audio line. I have worked a lot with JT modes and use 5.0K and DIGU in my slice setup. In fact I have created different profiles for digital modes, SSB, FM and RTTY.
  • K6OZY
    K6OZY Member ✭✭
    edited February 2017
    Alex is spot on on that.  You should NOT be using USB.

    Also, next time this happens, can you try existing DAX by finding the icon in the task bar, right clicking and exiting it.  Then restart it.   I've also seen the DAX system start dropping many sound packets and starts distorting too.    Rebooting the entire radio usually isn't necessary.
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited March 2017
    This looks like DAX buffer corruption from a long duration DPC event.  You should run LatencyMon and see if your PC is capable of running real-time audio processing   https://helpdesk.flexradio.com/hc/en-us/articles/202118698-Using-LatencyMon-to-collect-DPC-Latency-D...
  • rich
    rich Member
    edited March 2016

    The equalizer is manually turned off as well as the compressor.  I have also worked extensively with JT modes and have thousands of Qs all on USB.  This problem occurs ONLY after I have switched back from a voice or CW QSO.  See comments in the referenced thread.

  • rich
    rich Member
    edited March 2016


    Ran the Latency Monitor - here are the results:

    So it appears that there is a definite some problem with latency.  I'll follow the suggested remedies.

    Thanks! Rich, K3VAT

  • Andrew VK5CV
    Andrew VK5CV Member ✭✭
    edited March 2017
    Early days yet with 1.5 but DAX seems more fragile. I have done a lot of work and have reduced latency problems as indicated by LatencyMon. DAX 1.4 would remain clean for a while after being restarted. 1.5 goes feral almost immediately. Do wee need the ability to manage buffer size etc?
    Andrew de VK5CV
  • DrTeeth
    DrTeeth Member ✭✭
    edited December 2018
    I have also noticed this on JT modes using DIGU.
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    There were no changes made to DAX between v1.4.16 and v1.5.0.  This behavior is due to DPCs and they are system specific.  And the buffer size is allocated by the sound device API to maintain real-time streaming; a larger buffer will not mitigate this situation and would possibly aggravate other issues.  
  • Cal Spreitzer - N3CAL
    edited November 2015
    I also notice this on JT modes using DIGU.  It's  very frustrating because I had the same type results as Rich has from Latency Monitor several months ago!  Since then I built a new top of the line computer ( Intel I7 Gen 5 with 32 GB memory) and running Latency Monitor says I have no problems now but I still see the DAX DPC buffer issue frequently just by leaving the Flex on 24/7.    Stopping DAX Control Panel and restarting it seems to solve the problem but you really have to be vigilant monitoring your TX signal.  It just pops up intermittently. 


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