Hellschreiber

The Hellschreiber, also called the Feldhellschreiber or Hell-Schreiber, is a facsimile-based teleprinter invented by Rudolf Hell. Compared with contemporary teleprinters built on typewriter mechanisms, it was much simpler and more robust, with far fewer moving parts, and it could give intelligible communication even over very poor radio or cable links. It sends a line of text as a series of vertical columns, normally on a 7 by 7 pixel grid, as on-off signals at about 112.5 baud; at the receiver a spinning helical cylinder hammers dots onto a paper tape, and each column is printed twice to cover small timing errors. First developed in the late 1920s and used from the 1930s, mainly for landline press services, it served the German military in the Second World War and newswire services into the 1980s, and radio amateurs still use it today.