What could be wrong if you cannot decode an RTTY or other FSK signal even though it is apparently tuned in properly?
The mark and space frequencies may be reversed
You may have selected the wrong baud rate
You may be listening on the wrong sideband
All these choices are correct✓Bonne réponse
Explication
Three faults can leave the signal looking centered while producing no valid text: reversed mark/space tones, the wrong baud rate, or the wrong sideband, which itself swaps the tone polarity. Each condition must be checked separately, so every listed fault can explain the failure.