How to Fix WSJT-X FT8 Issues on a FT-991A
If WSJT-X randomly loses audio, stops decoding, crashes when transmitting, or becomes unstable after a few FT8 cycles, this guide walks through a known-stable FT-991A configuration.
This setup has been proven reliable on Windows systems and avoids the most common Yaesu USB audio and CAT control failure points. Follow the steps in order — do not skip anything.
🔒 Do These Exactly (Most Important First)
1️⃣ FT-991A Menu Settings (Critical)
Set these values directly on the radio:
- Menu 031 – CAT Rate: 38400
- Menu 032 – CAT TOT: 100 ms
- Menu 033 – CAT RTS: Disable
- Menu 034 – CAT DTR: Disable
- Menu 037 – USB MOD Level: 50
- Menu 038 – DATA MODE: USB
- Menu 039 – DATA USB SELECT: Rear
- Menu 040 – DATA VOX: Disable
Important: Do NOT use DATA-U mode. Do NOT use VOX for FT8. VOX + USB causes lockups and crashes — always use CAT PTT.
2️⃣ Windows Sound Settings (This Is Usually the Real Culprit)
The FT-991A USB audio driver must run at 48 kHz. Any mismatch will eventually crash WSJT-X.
Recording Device
- Device: USB Audio CODEC (FT-991A)
- Format: 16-bit, 48000 Hz
- ❌ Disable Enhancements
- ❌ Disable AGC
- ❌ Disable Noise Suppression
- ❌ Uncheck “Allow applications to take exclusive control”
Playback Device
- Device: USB Audio CODEC (FT-991A)
- Format: 16-bit, 48000 Hz
- ❌ No enhancements
- ❌ No exclusive mode
⚠️ If either side is set to 44.1 kHz, instability is guaranteed.
Very Important: Do NOT set the FT-991A as the Windows default mic or speaker. Use laptop speakers or headphones for system audio.
3️⃣ WSJT-X Settings (Do Not Let It Auto-Pick)
Audio Tab
- Input: USB Audio CODEC (FT-991A)
- Output: USB Audio CODEC (FT-991A)
- ❌ Do NOT use “Default”
- ❌ Do NOT use WASAPI
Radio Tab
- Rig: Yaesu FT-991A
- Serial Port: COM port assigned to the radio
- CAT Control: USB
- PTT Method: CAT
- Mode: USB
- Split Operation: Fake It (recommended)
Click Test CAT and Test PTT. Both should turn green instantly.
4️⃣ Prevent Windows from Stealing the Device
Windows and other apps will grab the USB Audio CODEC and break WSJT-X.
- Close browsers, Discord, OBS, and audio meters
- Do not leave YouTube or streaming apps running
Disable USB power saving:
- Device Manager → USB Root Hub → Power Management
- ❌ Uncheck “Allow the computer to turn off this device”
5️⃣ Run WSJT-X as Administrator
This improves USB audio stability on Yaesu radios, especially under Windows 11.
🔍 If It Still Crashes — One Last Fix That Works
- Power off the FT-991A
- Unplug the USB cable
- Reboot the PC
- Reconnect the radio
- Let Windows reinstall the USB Audio CODEC
- Re-select devices in WSJT-X (do not reuse old selections)
Final Check (Most Important)
- WSJT-X input level: 30–60 dB
- No clipping
- RX stays active across many FT8 cycles
Once dialed in, this setup will run FT8 on a FT-991A for days without a hiccup.