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Radioteletype (RTTY) is a telecommunications system consisting of two or more teleprinters using radio as the transmission medium.

Landline teleprinter operations began in 1849 when a circuit was put in service between Philadelphia and New York City.^[1] Emile Baudot designed a system using a five unit code in 1874 that is still in use today. Teleprinter system design was gradually improved until, at the beginning of World War II, it represented the principal distribution method used by the news services.

Radioteletype evolved from these earlier landline teleprinter operations. Commercial RTTY systems were in active service between San Francisco and Honolulu as early as April 1932 and between San Francisco and New York City by 1934.^[2] The US Military used radioteletype in the 1930s and expanded this usage during World War II. The Navy called radioteletype RATT and the Army Signal Corps called radioteletype SCRT, an abbreviation of Single-Channel Radio Teletype. The Military used frequency shift keying technology and this technology proved very reliable even over long distances.

Contents 1 Early Amateur Radioteletype History 2 How it works 3 Slow by modern standards 4 Spectrum efficiency 5 Primary users 6 Pronunciation 7 Spectrum usage 8 Media 9 References 10 See also 11 External links

After World War II, Amateur Radio operators in the United States started to receive obsolete but usable Teletype Model 26 equipment from commercial operators with the understanding that this equipment would not be used for or returned to commercial service. US Amateur Radio operation began on 2 meters using audio frequency shift keying (AFSK). Operation on 80 meters, 40 meters and the other High Frequency (HF) amateur radio bands was initially accomplished using make and break keying since frequency shift keying (FSK) was not yet authorized. In early 1949, the first transcontinental two-way RTTY QSO was accomplished on 11 meters using AFSK between W1AW and W6PSW.^[3] FSK continued to remain off-limits on HF until February, 1953 when the FCC amended Part 12 of the Regulations. The amended Regulations permitted FSK in the non-voice parts of the 80, 40 and 20 meter bands and also specified the use of single channel 60 words-per-minute five unit code corresponding to ITA2. A shift of 850 Hertz plus or minus 50 Hertz was specified. Amateur Radio operators also had to identify their station callsign at the beginning and the end of each transmission and at ten minute intervals using International Morse Code. Use of this wide shift proved to be a problem for Amateur Radio operations. Commercial operators had already discovered that narrow shift worked best on the HF bands. After investigation and a petition to the FCC, Part 12 was amended, in March 1956, to allow Amateur Radio Operators to use any shift that was less than 900 Hertz.

By the late 1950s, Amateur Radio operators outside of Canada and the United States began to acquire surplus teleprinter and receive permission to get on the air. The first recorded RTTY QSO in the UK occurred in September 1959 between G2UK and G3CQE. A few weeks later, G3CQE had the first G/VE RTTY QSO with VE7KX.^[4] This was quickly followed up by G3CQE QSOs with VK3KF and ZL3HJ.^[5] Information on how to acquire surplus teleprinter equipment continued to spread and before long it was possible to work all continents on RTTY.

During the early days of Amateur RTTY, the Worked All Continents – RTTY Award was conceived by the RTTY Society of Southern California and issued by RTTY Journal.^[6] The first Amateur Radio station to achieve this WAC – RTTY Award was VE7KX.^[7]. The first stations recognized as having achieved single band WAC RTTY were W1MX (3.5 MHz); DL0TD (7.0 MHz); K3SWZ (14.0 MHz); W0MT (21.0 MHz) and FG7XT (28.0 MHz).^[8] The ARRL began issuing WAC RTTY certificates in 1969.

By the early 1970s, Amateur Radio RTTY had spread around the world and it was finally possible to work more than 100 countries via RTTY. FG7XT was the first Amateur Radio station to claim to achieve this honor. However, Jean did not submit his QSL cards for independent review. ON4BX, in 1971, was the first Amateur Radio station to submit his cards to the DX Editor of RTTY Journal and to achieve this honor.^[9] The ARRL began issuing DXCC RTTY Awards on November 1, 1976.^[10] Prior to that date, an award for working more than 100 countries on RTTY was only available via RTTY Journal.

On January 7, 1972, the FCC amended Part 97 to allow faster RTTY speeds. Four standard RTTY speeds were authorized, namely, 60 (45 baud), 67 (50 baud), 75 (56.25 baud) and 100 (75 baud) words per minute. Many Amateur Radio operators had equipment that was capable of being upgraded to 75 and 100 words per minute by changing teleprinter gears. While there was an initial interest in 100 words per minute operation, many Amateur Radio operators moved back to 60 words per minute. Some of the reasons for the failure of 100 words per minute HF RTTY included poor operation of improperly maintained mechanical teleprinters, narrow bandwidth terminal units, continued use of 170 Hz shift at 100 words per minute and excessive error rates due to multipath distortion and the nature of ionospheric propagation.

The FCC approved the use of ASCII by Amateur Radio stations on March 17, 1980 with speeds up to 300 baud from 3.5 to 21.25 Mhz and 1200 baud between 28 and 225 MHz. Speeds up to 19.2 kilobaud was authorized on Amateur frequencies above 420 MHz.^[11]

The requirement for Amateur Radio operators to identify their station callsign at the beginning and the end of each digital transmission and at ten minute intervals using International Morse Code was finally lifted on June 15, 1983.

RTTY uses a variety of different modulation methods, of which frequency shift keying is the most common.

The FSK RTTY signal starts at the teleprinter as groups of dc impulses, known as marks and spaces. Each group represents an alphanumeric character or a function. As the operator types characters and functions on the teleprinter, the connected originating transmitter's carrier is shifted by a predefined frequency, usually 170 or 425 Hz. At the receiving end, the shifted carrier is detected and the audio output is normally fed to an external Terminal Unit ("Demodulator") which converts the audio signal to dc impulses which operate the teleprinter. These FSK signals can be heard on a communications radio receiver equipped with a BFO (beat frequency oscillator), and have a "beedle-eeeedle-eedle-eee" sound, usually starting and ending on the high-pitched tone.

The most common test-signal is a series of "RYRYRY" characters, as these form an alternating tone pattern exercising all bits and are easily-recognized.

• Coding used is typically 5-bit ITA2 code (also known as the Baudot code), which is asynchronously with start and stop bits.
• At least one common RTTY system uses 6-bit ITA2 character codes.
• More modern systems use 7-bit or 8-bit codes, e.g. ASCII.

Many RTTY operators had equipment which featured paper punch-tape readers. The operator would type the message on the TTY keyboard, which would punch the code into the tape. The tape could be re-done as desired, then transmitted at a steady, high rate, without typing errors. A tape could be reused, and in some cases - especially for use with ASCII on NC Machines - might be made of plastic or even very thin metal material in order to be reused many times.

RTTY is extremely slow by modern standards; a typical baud rate for RTTY operation is 45.45 baud (approximately 60 words per minute). This is one reason that RTTY has declined in commercial popularity, as faster, computerized transmission modes were developed, using less-expensive equipment.

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. Part of this is due to the fact that FSK, like FM, always operates at maximum power. FSK is the single most demanding mode for transmitter equipment.

Principally users that need robust shortwave communications

• All Military Departments, all over the world, (using cryptography)
• Diplomatic services, all over the world, (using cryptography)
• Weather reports are transmitted by the US Coast Guard nearly continuously
• RTTY systems are also fielded by amateur radio operators, and are popular for long-distance contacts

The pronunciation of RTTY is disputed

• In very few applications, notably the U.S. military in WWII and the fifties, radio teletype is known by the acronym RATT (RAdio TeleType)rather than RTTY.

• Sailmail, a commercial HF mail system
• SITOR, (SImplex Teleprinting Over Radio) an commercial RTTY variant with error control (the Radio Amateur version is called "AMTOR")
• PACTOR, a packet SITOR variant, developed by Radio Amateurs in Germany
• Hellschreiber, a FAX-RTTY hybrid, very old system from the 30's
• ACARS, used by commercial aviation – packet based
• Navtex, used for maritime weather reports, with FEC error control code,
• MT63, developed and used by Radio Amateurs and some government agencies
• Olivia MFSK from the creator of MT63
• PSK31 & PSK63 developed and used by Radio Amateurs
• MFSK
• Multiple frequency-shift keying COQUELET and PICCOLO, also referred to generically as Polytone
• CLOVER2000 developed by HAL company, USA, for Radio Amateur application
• Q15X25, a Radio Amateur created packet format(AX25), similar to the commercial X25 standard
• BARTG, The British Amateur Radio Teledata Group

• Getting Started on RTTY, Getting started on RTTY using MMTTY
• RTTY Basics, a radio amateur perspective
• RTTY.COM, a repository of Amateur RTTY information