Almost everyone now knows what a fax is! A data transmission ,then, is created in a very similar way but is transmitted over the airwaves as a radio signal instead of over a phone line. There are many different forms of data transmission, most common being WEFAX or, WEather FAX, usually transmitted from satellite to a station on earth. Slow Scan Television, Used most by radio amateurs though also used by the various space agencies , mainly the Russian Mir space station ,sadly, no longer with us! to send single frame pictures via radio. We also have Morse, which needs no explanation , and RTTY, pronounced ritty which is a radio teletype mode most used by amateurs now, though once a mainstay of marine communications.
Data Modes , as far as the radio amateur are concerned, were at one time both expensive and difficult in that they required special `interfaces` and software to get up and running!
Things have, however, changed quite a lot with the advent of personal computers and sound card software which enables data to be decoded by the pc`s soundcard without the need for any further hardware! Software is readily available from the net!