RTTY-Radio Teletype Radioteletype (RTTY) is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations connected by radio rather than a wired link. These machines were later superseded by personal computers (PCs) running software to emulate teleprinters. Radioteletype evolved from earlier land line teleprinter operations that began in the mid-1800s. The US Navy Department successfully tested printing telegraphy between an airplane and ground radio station in 1922. Later that year, the Radio Corporation of America successfully tested printing telegraphy via their Chatham, Massachusetts, radio station to the R.M.S. Majestic. Commercial RTTY systems were in active service between San Francisco and Honolulu as early as April 1932 and between San Francisco and New York City by 1934. The US military used radioteletype in the 1930s and expanded this usage during World War II. From the 1980s, teleprinters were replaced by computers running teleprinter emulation software. The term radioteletype is used to describe both the original radioteletype system, sometimes described as "Baudot", as well as the entire family of systems connecting two or more teleprinters or PCs using software to emulate teleprinters, over radio, regardless of alphabet, link system or modulation. In some applications, notably military and government, radioteletype is known by the acronym RATT (Radio Automatic Teletype)There are several programs that allow you to receive and transmit via a computer.These include {MixW},{MMRTTY},{MultiPSK} to name a few. On hf and the internet these programs work very well only on hf it can be a little bit harder as band conditions effect them. On the website of rtty.com you can read the history of this mode and what is baudot.that is the type of codeing that is used either 7bit or 8bit information called mark spaces tones.these can be changed to 60wpm with a shift of 170hz the spacing alternates between to sets of tones  that are set at 2150hz and shifts 2125hz. at 50wpm 450hz shift and at 100wpm 850hz shift is used.These different shifts are used to be able to send more bits per second {BPS} of information and accurately.