CCIR 476 is a

character encoding Character encoding is the process of assigning numbers to graphical character (computing), characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using computers. The numerical v ...

used in radio data protocols such as

SITOR SITOR (SImplex Teletype Over Radio) is a system for transmitting text messages. It was developed in the 1960s by Koninklijke TNT Post as an improvement over radioteletype (RTTY). Although it uses the same frequency-shift keying (FSK) modulation use ...

, AMTOR and

Navtex NAVTEX (NAVigational TEleX), sometimes styled Navtex or NavTex, is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent maritime safety inf ...

. It is a recasting of the

ITA2 The Baudot code () is an early character encoding for telegraphy invented by Émile Baudot in the 1870s. It was the predecessor to the International Telegraph Alphabet No. 2 (ITA2), the most common teleprinter code in use before ASCII. Each Chara ...

character encoding, known as

Baudot code The Baudot code () is an early character encoding for telegraphy invented by Émile Baudot in the 1870s. It was the predecessor to the International Telegraph Alphabet No. 2 (ITA2), the most common teleprinter code in use before ASCII. Each ch ...

, from a five-bit code to a seven-bit code. In each character, exactly four of the seven bits are mark bits, and the other three are space bits. This allows for the detection of single-bit errors.

Technical details

The number of possible valid binary code values in CCIR 476 is the number of ways to choose 4 marks for 7 bit positions, and the number can be calculated using the

binomial coefficient In mathematics, the binomial coefficients are the positive integers that occur as coefficients in the binomial theorem. Commonly, a binomial coefficient is indexed by a pair of integers and is written \tbinom. It is the coefficient of the t ...

\ \textstyle \binom = \binom = 35\ .

Thus CCIR 476 has 3 additional

code point A code point, codepoint or code position is a particular position in a Table (database), table, where the position has been assigned a meaning. The table may be one dimensional (a column), two dimensional (like cells in a spreadsheet), three dime ...

s available over ITA2's 32 code points. The

protocol uses the additional three code points (denoted as SIA, SIB and RPT below) for idle, phasing, and repeat requests. In addition, some of the ordinary characters are reused as control signals. ''Service Information Signals''.

Character set

In these tables, the hexadecimal code values are converted from a binary representation, with 1 being mark, 0 being space, and the most significant bit given first. The international version of ITA2 is used here; note also the added non-ITA2 codes SIA, SIB and RPT, used by SITOR.

References

* {{Citation , editor-last=Schetgen , editor-first=Robert , title=The ARRL Handbook for Radio Amateurs , year=1995 , edition=Seventy-Third (1996) , publisher=The American Radio Relay League , location=Newington, CT , isbn=0-87259-173-5 , url-access=registration , url=https://archive.org/details/arrlhandbookforr00amer Character encoding Character sets Telegraphy Amateur radio