Editing Radioteletype (section)

==Technical specification==

The original (or "Baudot") radioteletype system is based almost invariably on the [[Baudot code]] or ITA-2 5 bit alphabet. The link is based on character asynchronous transmission with 1 start bit and 1, 1.5 or 2 stop bits. Transmitter modulation is normally [[Frequency-shift keying|FSK]] ([[Types of radio emissions|F1B]]). Occasionally, an AFSK signal modulating an RF carrier (A2B, F2B) is used on VHF or UHF frequencies. Standard transmission speeds are 45.45, 50, 75, 100, 150 and 300 baud.

Common carrier shifts are 85&nbsp;Hz (used on LF and VLF frequencies), 170&nbsp;Hz, 425&nbsp;Hz, 450&nbsp;Hz and 850&nbsp;Hz, although some stations use non-standard shifts. There are variations of the standard Baudot alphabet to cover languages written in Cyrillic, Arabic, Greek etc., using special techniques.<ref>{{cite book | author=Klingenfuss, J. |title=Radio Data Code Manual | edition=17th | publisher=Klingenfuss Publications | year=2003 | isbn=3-924509-56-5 | pages=129–134}}</ref><ref>{{cite web | url=http://xoomer.alice.it/ham-radio-manuals/scanning/Digitalsignalsfaq.html |author1=Scalsky, S.  |author2=Chace, M.  |name-list-style=amp | title=Digital Signals Frequently Asked Questions (Version 5), Section 1-H | year=1999 | publisher=World Utility Network (WUN) | access-date=2008-01-06 }}</ref>

Some combinations of speed and shift are standardized for specific services using the original radioteletype system:

* [[Amateur radio]] transmissions are almost always 45.45 baud &ndash; 170&nbsp;Hz, although 75 baud activity is being promoted by BARTG in the form of 4-hour contests.<ref>{{cite web|url=http://www.bartg.org.uk/documents/Contests/sprint75/BARTG%20Sprint75%20Contest%20rules%202010.pdf|title=BARTG SPRINT 75|access-date=2011-09-25|archive-url=https://web.archive.org/web/20150802150331/http://www.bartg.org.uk/documents/Contests/sprint75/BARTG%20Sprint75%20Contest%20rules%202010.pdf|archive-date=2015-08-02|url-status=dead}}</ref>
* Radio amateurs have experimented with ITA-5 (7-bit ASCII) alphabet transmissions at 110 baud &ndash; 170&nbsp;Hz.
* [[NATO]] military services use 75 or 100 baud &ndash; 850&nbsp;Hz.
* A few naval stations still use RTTY without encryption for CARB (channel availability broadcasts).<ref>{{cite book | title=Eavesdropping on the British Military | author=Cannon, M. | publisher=Cara Press | location=Dublin | year=1994 |pages=72–75}}</ref>
* Commercial, diplomatic and weather services prefer 50 baud &ndash; 425 or 450&nbsp;Hz.<ref name="Schedule radio broadcast">{{cite web
 |url        = https://www.dwd.de/DE/derdwd/it/_functions/Teasergroup/sendeplan_rtty.pdf?__blob=publicationFile&v=2
 |title      = Schedule radio broadcast
 |access-date = 2019-09-30
}}</ref>
* Russian (and in the past, [[Soviet Union]]) merchant marine communications use 50 baud &ndash; 170&nbsp;Hz.<ref>{{cite web | author=Tom Roach | url=http://ftp.funet.fi/pub/dx/text/utility/Soviet.rtty | title=Soviet.rtty | year=1991|access-date=2008-01-11}}</ref>
* RTTY transmissions on [[Low frequency|LF]] and [[Very low frequency|VLF]] frequencies use a narrow shift of 85&nbsp;Hz, due to the limited bandwidth of the antennas.