Receiving Hellschreiber with the RTL-SDR and an Upconverter
Over on YouTube user BSoD Badgers has uploaded a video showing reception of Hellschreiber on HF at 20m. To receive the HF frequencies he used a ham-it-up upconverter. He used SDR# to receive the signal and the Fldigi decoding software to decode the signal.
Hellschreiber is a fax-like communications mode used by amateur radio hobbyists.