Amateur radio enthusiasts have been at the forefront of experimentation and development since the very earliest days of radio. All over the world, radio amateurs use a wide range of modes and frequencies to communicate. When surplus teleprinters became available in the early 1950s, radio amateurs adapted them for their own use and the first modern digital mode was born. Half a century later, RTTY is still widely used, and has been joined by a great number of other modes.
Most software for digital modes use a soundcard to communicate with the radio, and a simple circuit to switch the radio to transmit. Examples of the PTT circuits used may be found here .