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{{for|the book series by Edgar Rice Burroughs|Amtor}}

'''AMTOR''' ('''Amateur Teleprinting Over Radio''') is a type of telecommunications system that consists of two or more electromechanical [[Teleprinter|teleprinters]] in different locations that send and receive messages to one another. AMTOR is a specialized form of [[Radioteletype|RTTY]] [[Communications protocol|protocol]]. The term is an acronym for Amateur Teleprinting Over Radio<ref name="Arabi">{{cite book|last=Akbar Arabi|first=Ali|title=Comprehensive Glossary of Telecom Abbreviations and Acronyms|date=14 September 2007|publisher=AUERBACH|isbn=978-1-4200-5866-6|url=https://books.google.com/books?id=DVoqmlX6048C&q=AMTOR|page=19}}</ref> and is derived from ITU-R recommendation 476-1 and is known commercially as SITOR (Simplex Telex Over radio) developed primarily for maritime use in the 1970s.<ref name="Williams-p173">{{cite book|title=The Illustrated Dictionary of Mass Communications|last=Williams|first=Jack|publisher=Lotus Press|date=2007-11-30|isbn=978-81-89093-46-4|url=https://books.google.com/books?id=_nBQfZ5zThAC&q=AMTOR|page=173}}</ref>  AMTOR was developed in 1978 by Peter Martinez, G3PLX, with the first contact taking place in September 1978 with G3YYD on the 2m Amateur band. It was developed on homemade [[Motorola 6800]]-based [[microcomputer]]s in assembler code. It was used extensively by [[amateur radio]] operators in the 1980s and 1990s but has now fallen out of use as improved PC-based data modes are now used and teleprinters became out of fashion.

AMTOR improves on RTTY by incorporating [[Error detection and correction|error detection]] or error correction techniques.<ref name="Williams-p15-16">{{cite book|title=The Illustrated Dictionary of Mass Communications|last=Williams|first=Jack|publisher=Lotus Press|date=2007-11-30|pages=15–16|isbn=978-81-89093-46-4|url=https://books.google.com/books?id=_nBQfZ5zThAC&dq=AMTOR&pg=PA84}}</ref> The protocol remains relatively uncomplicated and AMTOR performs well even in poor and noisy HF conditions. AMTOR operates in one of two modes: an error detection mode and an automatic repeat request ([[Automatic repeat request|ARQ]]) mode.

The AMTOR protocol utilizes a 7-[[bit]] code for each character, with each code-word having four mark and three space bits.  If the received code does not match a four-to-three (4:3) ratio, the receiver assumes an error has occurred.  In error detection mode, the code word will be dropped; in automatic repeat request mode, the receiver requests that the original data be resent. AMTOR also supports [[forward error correction|FEC]] in which simple bit-errors can be corrected.

AMTOR utilizes [[frequency-shift keying|FSK]], with a frequency shift of 170 Hz, and a symbol rate of 100 [[Baud]].

AMTOR is rarely used today, as other protocols such as [[PSK31]] are becoming favoured by amateur operators for real-time text communications.  The [[American Radio Relay League|ARRL]] has announced that as of August 17, 2009, it will be dropping AMTOR bulletin service in favor of the more popular [[MFSK16]] and [[PSK31]] modes.

{{listen|filename=AMTOR_sample.ogg|title=A sample AMTOR transmission|description=The text "Welcome to Wikipedia, the free encyclopedia that anyone can edit." sent as AMTOR FEC}}

==See also==
* [[SITOR]]
* [[NAVTEX]]
* [[Radioteletype]]

==Further reading==
* {{Cite web|title=Amtor, An Improved Error-Free RTTY System|author=J. P. Martinez G3PLX|publisher=[[QST]]|date=June 1981|url= http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/QS06-81-Martinez.pdf|accessdate=2019-08-30}}
* {{Cite web|title=M.476 : Direct-printing telegraph equipment in the maritime mobile service|publisher=[[ITU-R]]|date=2001-06-01|url= https://www.itu.int/rec/R-REC-M.476-5-199510-I/en|accessdate=2019-08-30}}

==Notes==
{{Reflist}}

{{Digital modes}}
{{Amateur radio topics}}

{{amateur-radio-stub}}

[[Category:Quantized radio modulation modes]]
[[Category:Digital amateur radio]]