Hellfax KF 108 (1956)  
         
 
Facsimile devices transmit documents with only black and white picture elements (pixels), e.g. printed or handwritten text or drawings. The Hellfax KF 108 was developed by Hell in 1956. It was mainly used by post offices for transmitting telegrams, but also for cheques, freight documents, signatures, or for text documents with a non-Latin alphabet. The device can transmit an A5-document in 3.5 minutes, and it can operate as a transmitter or as a receiver. About 100,000 devices were produced by Siemens since the fifties (Hell did not have the capacity for large scale production).
 
   
         
 
When operating as a transmitter, the document to be sent is mounted on a drum, which rotates
and moves along a scanning unit. A scanning light is directed on the drum from below, and the
reflected light is converted into electrical signals by means of a photo cell. The signals represent-
ing the black and white pixels are then sent over the transmission line.
 
 
Klein Fax KF 108 Datenuebertragung
 
         
 
When operating as a receiver, the received electrical signals actuate a tiny inked recording
wheel by electromagnetic force, which writes the black pixels on a sheet of normal paper
mounted on the drum.