RTTY

RTTY, short for radioteletype, is a digital mode for transmitting text over radio using teletypewriters or computer terminals connected to a transmitter. Data are encoded with a Baudot code and sent as audio-frequency shift keying (FSK) on an RF channel, using two tones to represent mark and space.

RTTY has its origins in early teleprinter networks of the 1920s and 1930s and reached widespread use in the mid-20th century by military, government, and press services. While its prominence has diminished with newer digital modalities, it retains a niche following among hobbyists and some professional users. Modern hardware and software enable RTTY operation with affordable radio gear and computer interfaces.

Technically, RTTY employs two audio tones to convey the binary states of the transmission. It uses a 5-bit Baudot code (ITA2) with shift states for letters and figures, allowing a compact character set. The typical amateur RTTY speed is around 45.5 baud. The format is relatively simple and robust in the presence of noise, though the data rate is slow compared with contemporary digital modes. Accurate tuning, stable timing, and proper shift handling are important for reliable reception.

In modern practice, RTTY can be run with dedicated teletype equipment or via computer sound-card modems and software such as fldigi or MMTTY. A radio, a suitable interface, and software on a PC or similar device are commonly used on HF amateur bands, where long-distance text transmission remains feasible even under challenging conditions.

RTTY remains a foundational part of telecommunication history; related topics include the Baudot code and traditional teleprinter technology.