Teletype

One of the early innovations in the field of Radio was the teletypewriter, more commonly known as the "teletype". It was a huge advancement in technology. It allowed transmission of printed material over the radio waves. As an operator typed on a standard keyboard, the typing generated a different tone for each letter. That tone was then broadcast over the airwaves to another teletype station. That station would tune into the string of tones, and convert them back to letters, and then print them on a typing device. This was really revolutionary technology at the time.

HAM operators still use a form of teletype known as RTT or PSK-31. It works almost identical to the original teletypes, but the terminals are personal computers instead of typewriter type devices. It works, though just like the early systems in that the information is conveyed by broadcasting a series of tones over the airwaves.