HELLSCHREIBER is a method of sending and receiving text using fax style technology.
This mode has been around since before World War II.
The most popular version (Feld-Hell) is the method of choice for HF operation.
It is an on-off keyed system with 122.5 dots/second, or about a 35 WPM text rate, with a narrow bandwidth (about 75 Hz).
As with telephone based fax machines the received text appears on the screen looking like a “rough” photocopy.