Radio Teletype (RTTY) has its roots in early teleprinter technology, which emerged in the 1920s and 1930s as a means of long-distance text communication. Initially used over landlines by news agencies, railroads, and military services, teleprinters were later adapted for radio transmission. By the 1930s, engineers began experimenting with sending teletype signals over radio waves, laying the groundwork for what would become RTTY.

During World War II, RTTY saw widespread use in military operations, particularly by the U.S. Army Signal Corps and the Navy. It allowed for the rapid and secure transmission of messages, ranging from battlefield orders to intelligence reports. The system’s speed and efficiency made it invaluable, and it became a standard method of military communication. After the war, surplus military teleprinters, such as the Teletype Model 15 and Model 28, found their way into the hands of amateur radio operators, who began using them to send and receive text messages over HF (shortwave) radio bands.

RTTY employs Frequency Shift Keying (FSK), where two distinct frequencies represent binary states: "mark" (logic 1) and "space" (logic 0). The Baudot code, a 5-bit character encoding system, is then used to convert these binary states into readable text.

After the war, surplus military teleprinters became accessible to amateur radio operators, who adapted them for use over HF (shortwave) bands. RTTY used the Baudot code, a 5-bit character encoding scheme, to transmit text. Unlike Morse code, which required manual interpretation, RTTY allowed for fully automated text transmission and reception. Communication was achieved through **Frequency Shift Keying (FSK)**, where two distinct audio tones represented binary states—one for "mark" (typically the higher frequency) and one for "space" (typically the lower frequency). A standard frequency shift of 170 Hz became common among amateur operators, though commercial and military systems sometimes used larger shifts.

Throughout the 1950s and 1960s, RTTY became the backbone of radio-based news distribution and military communication. News agencies like Reuters and the Associated Press relied on it to transmit wire reports globally. However, as newer digital communication methods emerged in the late 20th century, RTTY gradually declined in mainstream use. The advent of satellite communication, packet radio, and internet-based messaging rendered it obsolete for most commercial and military applications.

As technology advanced in the 1960s and 1970s, automatic decoding systems improved, reducing the need for human operators to manually interpret transmissions. However, despite its efficiency, RTTY gradually declined in commercial and military use with the rise of satellite communications and newer digital transmission methods. By the 1990s, it had been largely replaced by more advanced protocols such as AMTOR, Pactor, and PSK31.

Despite its decline in mainstream communication, RTTY has remained popular among amateur radio operators. Today, it is primarily used in contests and DXing, where radio enthusiasts compete to make as many contacts as possible across the world. The introduction of software-defined radios and digital signal processing has further enhanced RTTY’s reliability, allowing operators to send and receive messages with nothing more than a computer and a radio transceiver.

Though RTTY is no longer a dominant mode of communication, it holds a significant place in radio history. It represents one of the earliest forms of digital text transmission and remains an enduring part of amateur radio culture.