A Brief History of Radioteletype

Radioteletype — RTTY — is a method of transmitting printed text by radio. A sending station encodes typed characters using frequency-shift keying (FSK): a “mark” frequency for a binary 1, a “space” frequency for a binary 0. A receiving station decodes these shifts 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.

The five-bit encoding at the heart of every RTTY transmission has two fathers. French telegraph engineer Émile Baudot invented the five-bit concept in 1870 for a tape printer of his own design. New Zealand-born engineer Donald Murray refined and extended it around 1905 into the standard the world actually adopted: ITA2.

Baudot’s system — standardized as ITA1 (International Telegraph Alphabet No. 1) — assigned codes to make them easy for operators to learn. His machine was a tape printer; it had no need for line feed or carriage return codes. Five bits yields 32 possible combinations; Baudot used two shift states — Letters and Figures — to serve double duty, providing the full uppercase alphabet plus digits and punctuation.

Murray’s redesign addressed a different set of requirements. He was developing a page printer — a machine that printed on a continuous roll of paper, as modern teleprinters do — and a page printer requires line feed and carriage return codes that ITA1 simply lacked. Murray also rethought the entire code assignment from scratch, applying an engineering principle Baudot had not used: minimize mechanical wear. The most frequently typed characters received codes with the fewest punched holes, reducing wear on the perforating mechanism. The result was a fundamentally different code that happened to share the same five-bit structure.

Murray’s code was adopted internationally as ITA2 (International Telegraph Alphabet No. 2). It is ITA2 — not ITA1 — that all RTTY uses, including the ITTY broadcasts on this site. Each character is transmitted as a sequence of five equal-duration mark or space intervals. At 45.45 baud — the North American amateur standard — 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: RTTY.COM on top, DE W2TTY on the bottom. Anyone who knows the code can read them hole by hole.

In 1902, a young electrical engineer named Frank Pearne arrived in Chicago with an idea and a letter of introduction to Joy Morton — of Morton Salt. Morton was intrigued and consulted a friend, Charles L. Krum, a distinguished mechanical engineer. A laboratory was set up in the attic of Morton’s cold storage company, and experimental work on printing telegraphy began.

After about a year, Pearne lost interest and moved on. Krum continued. By 1906 he had a promising working model, and his son Howard — a newly graduated electrical engineer — joined him. On October 5, 1907, the Morkrum Company was incorporated, the name combining Morton and Krum, with capital of $150,000.

The first commercial installation came in 1910, when Postal Telegraph placed Morkrum equipment on its New York to Boston circuit. The test proved highly successful. Western Union followed in 1912. Railroad installations multiplied. When the United States entered World War I, military demand for printing telegraphy accelerated rapidly — unlike Morse code, the new machines required no operators who could read dots and dashes. Anyone could read the printed output.

Meanwhile, in New York, Edward Kleinschmidt had founded Kleinschmidt Electric Company, also manufacturing printing telegraph instruments and serving many of the same commercial customers. The competition between the two firms eventually produced a patent dispute, and in 1924 the dispute was resolved by merger. The Morkrum-Kleinschmidt Corporation was formed, with Sterling Morton as president and Edward Kleinschmidt and Howard Krum as vice presidents.

In December 1928, the corporate name was simplified to Teletype Corporation — the product trademark had become better known than either of the original company names, and the consolidation was complete. The founding years of printing telegraphy are documented in two primary sources available on this site: Howard Krum’s own manuscript account of the Morkrum years and the Teletype Corporation’s retrospective booklet from 1958.

In 1930, the Teletype Corporation was acquired by AT&T and became a subsidiary of Western Electric. Already the dominant manufacturer of printing telegraph equipment in North America, Teletype now had the resources to develop its landmark product line through the mid-century decades of peak commercial telegraphy.

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.

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.