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is a facsimile-based teleprinter invented by Rudolf Hell. It has since been emulated on computer sound cards by amateur radio operators; the resulting mode is referred to as Hellschreiber, Feld-Hell, or simply Hell. "Hellschreiber" translates into English as "Light Writer," "Bright Writer," or "Clear Writer," and is a pun on the name of its inventor (Hell (the adjective) is German for "light," the adverb is "bright.")
It was developed at the end of the 1920s, and has the advantage of being capable of providing intelligible communication even over very poor quality radio or cable links. During WW2 it was sometimes used by the German military in conjunction with the Enigma encryption system.