Introduction
Working with Telex messages or amateur radio RTTY? ITA2 (International Telegraph Alphabet No. 2) is the 5-bit teleprinter code that was the global standard for Telex service from the 1930s through the 1980s. Based on Donald Murray's 1901 modification of Baudot's original code, ITA2 uses LTRS and FIGS shift characters to encode 58 symbols in just 32 code positions. This tool encodes text to ITA2 and decodes 5-bit ITA2 sequences back to text, all in your browser.
What this tool does
- Encodes text into 5-bit ITA2 code with space-separated binary output.
- Decodes 5-bit ITA2 binary sequences back to text, handling LTRS/FIGS shift characters.
- Supports letters (A-Z), figures (digits, punctuation), and control characters (space, CR, LF).
- Uses the international ITA2 code assignments as standardized by CCITT in 1932.
- Outputs binary in 5-bit groups separated by spaces for readability.
- Processes all data locally with no server communication.
How this tool works
In Encode mode, type your text and the tool converts each character to its 5-bit ITA2 code. The tool automatically inserts LTRS (11111) and FIGS (11011) shift characters when switching between letter and figure modes. The output is space-separated 5-bit groups. In Decode mode, paste a sequence of 5-bit codes (spaces are ignored) and the tool interprets them according to the current shift state. The Swap button toggles between modes.
How ITA2 encoding works
ITA2 was standardized by the CCITT (Comite Consultatif International Telephonique et Telegraphique, now ITU-T) in 1932 as the International Telegraph Alphabet No. 2. It was based on Donald Murray's 1901 modification of Emile Baudot's original 1870s code. Murray redesigned the character assignments to minimize mechanical wear on teleprinter equipment by assigning fewer punches to frequently used letters. The result was a code that was not compatible with Baudot's original ITA1. ITA2 uses 5 bits per character, providing 32 code positions. Two positions are reserved for shift characters: LTRS (11111) switches to letters mode and FIGS (11011) switches to figures mode. This allows 30 remaining codes to represent 60 characters (30 in each mode). The letters mode contains A-Z plus space, CR, and LF. The figures mode contains digits 0-9, common punctuation, and control codes like BELL and WRU (Who aRe yoU). The WRU code caused the receiving machine to send an identification stream back to the sender, an early form of station identification. The United States used a slightly different variant called USTTY (US Teletypewriter), which differed from ITA2 in several figures-shift assignments. ITA2 was the workhorse code for Telex service, news wire services, diplomatic cables, and bank communications throughout the mid-20th century. It was gradually replaced by 7-bit ASCII (standardized in 1963, matured in 1967) as computers adopted ASCII for inter-system communication. Amateur radio operators still use ITA2 for RTTY (Radio Teletype) transmissions on HF bands. The PRC68 reference guide provides a comprehensive comparison of ITA2 and USTTY code assignments.
How to use this tool
- Select Encode mode and type your text. Letters, digits, and common punctuation are supported.
- The tool outputs 5-bit binary codes separated by spaces, with LTRS/FIGS shift codes inserted automatically.
- To decode, select Decode mode and paste a sequence of 5-bit codes. Spaces between codes are ignored.
- The tool interprets each 5-bit code according to the current LTRS or FIGS mode and outputs the decoded text.
- Use the Swap button to toggle between encoding and decoding.
Real-world examples
Encoding a Telex message
Input: 'HELLO'. The tool starts with LTRS shift (11111), then encodes H (10100), E (00001), L (10010), L (10010), O (11000). Output: '11111 10100 00001 10010 10010 11000'.
Encoding mixed content with figures
Input: 'PRICE $5.99'. The tool encodes P, R, I, C, E in LTRS mode, space, then FIGS shift (11011), then # (10100), 5 (10000), . (11100), 9 (11000), 9 (11000). The FIGS shift tells the receiver to interpret subsequent codes as figures.
Decoding an ITA2 RTTY signal
Input: '11111 10100 00001 10010 10010 11000'. The tool reads the LTRS shift, then decodes each 5-bit code in letters mode to produce 'HELLO'. If the input contains '11011' (FIGS), subsequent codes are interpreted as figures until an LTRS code appears.
Comparison with similar methods
| Method | Complexity | Typical use |
|---|---|---|
| ITA2 (Murray) | 5-bit fixed-length, stateful shift | Telex, RTTY, news wire (1930s-1980s) |
| Baudot (ITA1) | 5-bit fixed-length, stateful shift | Historical telegraphy (1870s-1930s) |
| ASCII | 7-bit fixed-length, no shift | Modern computing, internet |
| Morse code | Variable-length | Early telegraphy, amateur radio CW |
Limitations or considerations
This tool implements the international ITA2 standard, not the US TTY (USTTY) variant. The USTTY variant differs in several figures-shift character assignments (notably J, S, V, Z, F, G, H). The character set is limited to uppercase letters, digits, and basic punctuation. Lowercase letters are not supported. Some ITA2 code positions (notably FIGS F, G, H) had varying assignments across national implementations. The tool does not model start/stop bits or the physical teleprinter frame structure. Control characters like BELL and WRU are decoded but not displayed.
Frequently asked questions
What is the difference between ITA2 and Baudot code?
Baudot code (ITA1) was Emile Baudot's original 1870s encoding. ITA2 was standardized in 1932 based on Donald Murray's 1901 redesign. They use different character assignments for the same 5-bit codes and are not compatible. ITA2 was the global standard for Telex service. This tool implements ITA2; use the Baudot Code tool for ITA1.
What is USTTY and how does it differ from ITA2?
USTTY (US Teletypewriter) is the American variant of ITA2, used by Western Union, Bell System, and AT&T TWX. The letter assignments are identical to ITA2, but several figures-shift characters differ (notably $, !, &, #, and ' are in different positions). European Telex messages sometimes printed garbled punctuation on American receivers due to these differences.
Is ITA2 still used today?
Yes, in amateur radio. RTTY (Radio Teletype) transmissions on HF bands commonly use ITA2 at 45.45 baud (60 words per minute) or 50 baud. Many amateur radio transceivers include built-in ITA2 RTTY support. ITA2 is also used in some legacy Telex networks that remain operational for specific industries.
Why does ITA2 use shift characters instead of more bits?
When ITA2 was designed, telegraph infrastructure was built around 5-bit equipment. Adding more bits would have required entirely new hardware. The shift mechanism doubled the character set without changing the physical encoding, making it a practical solution for the electromechanical technology of the era.
Conclusion
ITA2 was the backbone of global teleprinter communication for over 50 years, carrying Telex messages, news wire copy, and diplomatic cables. This tool implements the international ITA2 standard for encoding and decoding. For the original Baudot code (ITA1), use the Baudot Code tool on this site. Check out the related Morse code translator for comparison with earlier telegraph codes.