Radioteletype (RTTY) is a telecommunications system consisting of two teleprinters linked by a radio link.
RTTY uses a variety of different modulation methods, of which frequency shift keying are the most common. The coding used is the 5-bit ITA2 code (also known as the Baudot code), which is used asychronously with start and stop bits.
RTTY is not fast by modern standards; a typical baud rate for RTTY operation was 45 baud (approximately 60 words per minute). If upgraded to a "100 wpm wheel" one could achieve a rate of 75 baud, but hams generally did not use this faster speed.
The combination of low baud rate with robust FSK modulation makes RTTY highly resistant to most forms of radio interference, second only to Morse code.
RTTY systems are also fielded by radio amateurs.
Those who actively engaged in amateur RTTY communications pronounced RTTY not by its intials but as "ritty".
In a few applications, notably the U.S. military, radio teletype is known by the acronym RATT rather than RTTY.