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'Radioteletype' ('RTTY') is a telecommunications system consisting of two or more teleprinters using radio as the transmission medium.
Early RTTY operators used equipment built for Bell System wire-linked Teletype(tm) systems. When ham radio operators began using this equipment for RTTY, they were required to sign agreements not to use the equipment for commercial purposes. This equipment was expensive and required periodic maintenance.
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 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 local beat frequency oscillator, and have a "beedle-eeeedle-eedle-eee" sound, usually starting and ending on the high-pitched tone.
Experienced RTTY operators are able to recognize some FSK patterns by ear. The most common test/idle signal is a series of "RY" 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 used 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 bytes.
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 might be made of plastic or even metal in order to be reused many times.
RTTY is extremely slow by modern standards; a typical baud rate for RTTY operation was 45.45 baud (approximately 60 words per minute). This is one reason that RTTY has declined in 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
★ Various navies of the world
★ Various armies of the world
★ Diplomats, especially in Africa and parts of Asia
★ 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, radio teletype is known by the acronym RATT rather than RTTY.
★ Those who are actively engaged in amateur RTTY communications pronounce RTTY not by its initials but as "ritty".
★ Sailmail, a commercial HF mail system
★ SITOR, an RTTY variant with error control.
★ PACTOR, a packet SITOR variant
★ Hellschreiber, a FAX-RTTY hybrid
★ ACARS, used by commercial aviation – packet based
★ Navtex, used by maritime navigation
★ MT63, used by Hams and some government agencies
★ Olivia MFSK from the creator of MT63
★ PSK31 & PSK63
★ MFSK
★ Multiple frequency-shift keying COQUELET and PICCOLO, also referred to generically as Polytone
★ CLOVER2000
★ Q15X25, a HAM created packet format
★ RTTY Basics, a radio amateur perspective
Early RTTY operators used equipment built for Bell System wire-linked Teletype(tm) systems. When ham radio operators began using this equipment for RTTY, they were required to sign agreements not to use the equipment for commercial purposes. This equipment was expensive and required periodic maintenance.
| Contents |
| How it works |
| Slow by modern standards |
| Spectrum efficiency |
| Primary users |
| Pronunciation |
| Spectrum usage |
| Media |
| See also |
| External Links |
How it works
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 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 local beat frequency oscillator, and have a "beedle-eeeedle-eedle-eee" sound, usually starting and ending on the high-pitched tone.
Experienced RTTY operators are able to recognize some FSK patterns by ear. The most common test/idle signal is a series of "RY" 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 used 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 bytes.
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 might be made of plastic or even metal in order to be reused many times.
Slow by modern standards
RTTY is extremely slow by modern standards; a typical baud rate for RTTY operation was 45.45 baud (approximately 60 words per minute). This is one reason that RTTY has declined in 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.
Spectrum efficiency
RTTY and Packet spectrum efficiency compared with respect to {bits/second} thruput
Primary users
Principally users that need robust shortwave communications
★ Various navies of the world
★ Various armies of the world
★ Diplomats, especially in Africa and parts of Asia
★ 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
Pronunciation
The pronunciation of RTTY is disputed
★ In very few applications, notably the U.S. military, radio teletype is known by the acronym RATT rather than RTTY.
★ Those who are actively engaged in amateur RTTY communications pronounce RTTY not by its initials but as "ritty".
Spectrum usage
Comparisons of MT63, RTTY and HF Packet spectrum
Media
See also
★ Sailmail, a commercial HF mail system
★ SITOR, an RTTY variant with error control.
★ PACTOR, a packet SITOR variant
★ Hellschreiber, a FAX-RTTY hybrid
★ ACARS, used by commercial aviation – packet based
★ Navtex, used by maritime navigation
★ MT63, used by Hams and some government agencies
★ Olivia MFSK from the creator of MT63
★ PSK31 & PSK63
★ MFSK
★ Multiple frequency-shift keying COQUELET and PICCOLO, also referred to generically as Polytone
★ CLOVER2000
★ Q15X25, a HAM created packet format
External Links
★ RTTY Basics, a radio amateur perspective
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