If you can hear the transmission
strong and clear, but your software
doesn't, then you may be tuning to the exact frequency specified in the schedule, rather than ~2 (1.6, iirc) kHz below that. Look up SSB
and "upper sideband" if you want to understand the rationale.
Your WeatherFAX software
should have a spectrum indicator to help you tune it right. Put the fine tuning dial on the middle position, dial in a frequency 2 kHz below what you read, slooooowly move the fine tuning dial up until the spectrum thingie looks right.
The other thing that I had to deal with figuring WeatherFAX out was gain structure. Tecsun's line output is actually for headphones, which means it's too loud for a line input. On my laptop
, I have to put both Tecsun's volume and mic/line input gain fairly close to zero, or else there is distortion.