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Severe Audio Stuttering and RF Power Drops in FT8 - SmartSDR+ v4.1.5 & WSJT-X v3.0.0

albert
albert Member ✭✭
in SmartSDR+

Hi FlexRadio Support Team,

I am opening this ticket regarding a persistent modulation issue with my Flex-6500 since upgrading to SmartSDR v4.1.5.

Problem Description:When operating in FT8 using WSJT-X v3.0.0, the transmitted audio is severely "stuttered" or "hachured". This is immediately followed by correlated drops in RF output power. The issue appeared specifically after the migration to version 4.1.5.

Technical Environment:

  • Radio: Flex-6500 (Firmware v4.1.5).
  • Software: WSJT-X v3.0.0.
  • Time Sync: Verified with NetTime (+2ms offset).
  • Network: PC and Radio are on the same subnet, MTU 1500, Interrupt Moderation disabled on the NIC.

Troubleshooting already performed:

  1. Clean Sweep: I have performed a complete uninstallation of all SmartSDR versions (v2, v3, and v4) and FlexVSP. I manually deleted the %APPDATA% and Program Files FlexRadio folders before a clean reinstall of v4.1.5.
  2. Audio Configuration: Verified that DAX Audio TX and DAX Audio RX are strictly set to 16-bit, 48000 Hz in the Windows Sound Control Panel.
  3. Split Mode: Tested with Split set to "None", "Fake It", and "Rig" with no improvement.

Despite these steps, the "Scenario B" delay we saw earlier is resolved, but the stuttering modulation makes the radio unusable in digital modes.

Could you please advise if there is a known compatibility issue with the v4.1.5 DAX drivers on certain Windows builds or if there is a specific buffer setting I should adjust?

73's

ON5AM

Tagged:

Comments

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Hi

    No, this is not a known problem. The first thing you need to do is a full radio reset after exporting your profiles and saving them. We do suggest doing this in the SmartSDR v4.1.5 release notes. Others have reported similar experiences and a radio reset has resolved their issues.

    Give that a try.

  • albert
    albert Member ✭✭

    Thanks Mike,

    After performing a full Factory Reset of the radio and a "Clean Sweep" of the PC software, I am stuck in the following repetitive 3-cycle loop.

    • Cycle 1: The radio receives normally.
    • Cycle 2: Instead of switching to Transmit as expected by WSJT-X, the radio stays in Receive mode.
    • Cycle 3: The radio finally keys up (TX indicator turns red), but there is no RF carrier/output at all.

    Then the sequence repeats.

    Has anyone seen this "skipped cycle followed by empty carrier" behavior before?

  • albert
    albert Member ✭✭

    I open a ticket.

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