Poor PSK31 decoding with FLdigi

  • 2
  • Problem
  • Updated 4 years ago
  • Solved

I am puzzled by poor decoding of PSK31 signals with FLdigi and DXLabs Winwarbler on my Flex 6500. Generally, any signal less than -85 dBm is mostly gibberish with either digital application. Only very strong signals produce usable copy.

I’ve gone over my settings repeatedly, but have yet to identify any problems.  Here are the system and software configuration parameters:


Dell  9000 i7 920, 8GB, Win 7/64 bit with all updates


DAX v1.0.5.49

FLdigi 3.21.81

SmartSDR.xml  version dated 8-MAR-2014

CPU utilization 8-12% average


FLdigi configuration:

Capture: DAX Audio RX 1 (DAX RX Audio)

Playback: DAX Audio TX1 (DAX TX Audio)

PortAudio (enabled)

Converter: Medium Sync Interpolator (tried others)


SmartSDR settings for digital mode:

 DIGU  3.0 khz (tried many filters, including 100 hz and lower)

DAX button enabled

DAX Channel: 1  (set to peak slightly below 0 db, although I’ve tried lower levels  and have tried other DAX channels)


Windows 7 sound settings:

DAX RESERVED AUDIO RX1 (Ready)  2 Channel, 16 bit, 48000 Hz (DVD Quality)

DAX AUDIO TX1 (Ready), 2  Channel, 16 bit, 48000 Hz (DVD Quality)


I made hundreds of PSK31 contacts with a Flex 5000A using VAC  and FLdigi and could often get viable copy of signals not much above the noise floor.


Any advice or suggestions would be greatly appreciated.



Larry KB1VFU

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Larry Benoit

  • 65 Posts
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Posted 4 years ago

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Photo of Larry Benoit

Larry Benoit

  • 65 Posts
  • 15 Reply Likes
Official Response
Installation of SmartSDR v 1.3 did not resolve the problem nor did any of the suggestions in this thread. However, it was resolved with a fresh installation of Windows 7 and SmartSDR.

It is not clear whether the problem was due to the Windows audio subsystem or DAX. Whatever the origins, it appeared that the DAX stream was becoming subtlely distorted due to corruption of some component or buffer in the audio path.

Larry KB1VFU