A Brief History of Radioteletype

Radioteletype — RTTY — is a method of transmitting printed text by radio. A sending station encodes typed characters as audio tones using frequency-shift keying (FSK): a “mark” tone for a binary 1, a “space” tone for a binary 0. A receiving station decodes these tones and drives a mechanical teleprinter that types the message on paper. The result is a printed record — a hard copy — of everything transmitted.

The system requires no operator at the receiving end. The machine prints continuously as long as the transmitter is active and the signal is readable. In its commercial heyday, RTTY circuits ran 24 hours a day, delivering news, weather, financial data, and military communications to receivers around the world.

At the heart of every RTTY transmission is the Baudot code — a five-unit binary encoding invented by French telegraph engineer Émile Baudot in 1870 and standardized internationally as ITA2 (International Telegraph Alphabet No. 2). Five bits yields 32 possible combinations; by using two “shift” states — Letters and Figures — the same 32 codes serve double duty, providing the full uppercase alphabet plus digits and punctuation.

The genius of the Baudot code lies in its mechanical simplicity. Each character is transmitted as a sequence of five equal-duration mark or space intervals, making it ideal for electromechanical reproduction. At 45.45 baud — the North American standard for amateur RTTY — each character takes 22 milliseconds to transmit, yielding approximately 60 words per minute. The 75-baud standard allows approximately 100 WPM.

The punched tape strips at the top and bottom of this page encode real ITA2 Baudot: RTTY.COM on top, DE W2TTY on the bottom. Anyone who knows the code can read them hole by hole.

Founded in 1906, the Teletype Corporation manufactured the electromechanical machines that defined a century of telecommunications. Beginning with the crude mechanical printers of the early telegraphic era, Teletype progressively refined the technology into precision instruments that became standard equipment in newsrooms, military installations, weather services, and amateur radio shacks worldwide.

The company's landmark models — the Model 14, 15, 19, 28, 32, and 33 — each represented a significant advance in speed, reliability, and capability. The Model 15, introduced in the 1930s, became the dominant machine in American commercial telegraphy. The Model 28 of the 1950s brought modern industrial design to the product line. The Model 33, designed for data communications with ASCII encoding, bridged the gap between the mechanical telegraphy era and the computer age.

Teletype became a subsidiary of Western Electric and ultimately AT&T. When AT&T was broken up in 1984, Teletype ceased manufacturing. Millions of machines remained in service for years afterward; the last commercial RTTY circuits were not decommissioned until well into the 1990s.

See the Equipment section for technical reference on individual Teletype models and the terminal units used to interface them to radio.

For fifty years, the Associated Press, United Press International, and other news wire services ran around-the-clock RTTY circuits delivering copy to radio stations, television stations, and newspapers. The machines never slept. Rolls of yellow paper advanced continuously through clattering mechanisms, printing a ceaseless flow of dispatches from around the world.

The newsroom of a mid-twentieth-century radio station was defined by the sound of these machines — the background rhythm against which everything else happened. Editors tore copy from the machines, marked it up, and handed it to the newsreader. The wire service was the pipeline; the teletype machine was the tap.

The ITTY service recreates this experience. Content sourced from modern wire services is formatted and transmitted in authentic Baudot RTTY at the original machine speeds. Owners of restored Teletype machines can connect, tune their modem, and watch the news print just as it would have in 1965. See the ITTY section for connection details.

Amateur radio operators began experimenting with radioteletype in the late 1940s and early 1950s, initially using surplus commercial Teletype machines acquired as the wire services upgraded their equipment. The appeal was immediate: RTTY offered something no voice transmission could provide — a permanent printed record of every exchange.

By the late 1950s, amateur RTTY had its own community, its own frequencies, and its own art form. Operators exchanged character art — images constructed from Baudot characters and transmitted over the air in real time. The overstrike technique, which allowed multiple characters to print on the same position by sending a carriage return without a line feed, gave the art form a unique expressive range unavailable to typewriter artists. The gallery on this site preserves the best of that tradition.

The North American amateur RTTY standard — 45.45 baud (60 WPM), 170 Hz shift, lower sideband — remains the format of the ITTY broadcasts today.

History Hall collects first-hand accounts, memoirs, and biographical pieces from the people who lived the early years of radioteletype. The first two papers were submitted by Jim Haynes W6JVE while at the University of California, Santa Cruz. Contributions are welcome — contact W2TTY.