Editing Bell 103 (section)

{{Short description|Modem for computers released by AT&T in 1962}}
{{More citations needed|date=August 2023}}
[[File:Bell DataPhone 300.jpg|thumb|The Bell DataPhone 300 used the same protocol as the Bell 103. This modem is from 1978.]]
The '''Bell 103 modem''' or '''Bell 103 dataset''' was the second commercial [[modem]] for [[computer]]s, released by [[AT&T Corporation]] in 1963.<ref>{{cite web | url = https://content.time.com/time/specials/packages/article/0,28804,2023689_2023708_2023715,00.html | title = All-TIME 100 Gadgets: Bell 103 | author = Peter Ha | date = 25 October 2010 | access-date = 28 August 2023}}</ref><ref>{{cite magazine | title = From Morse to Modems: A Brief History of Telecommunications | journal = PC Magazine | date = July 1989 | page = 209 | author = Joseph J. Antinori}}</ref>  It allowed [[digital data]] to be transmitted over regular unconditioned [[telephone line]]s at a speed of 300 [[bits per second]].  It followed the introduction of the 110 [[baud]] [[Bell 101 modem|Bell 101 dataset]] in 1958.

The Bell 103 modem used [[audio frequency-shift keying]] to encode data.  Different pairs of audio frequencies were used by each station:

* The '''originating''' station used a mark tone of 1,270 [[Hertz|Hz]] and a space tone of 1,070&nbsp;Hz.
* The '''answering''' station used a mark tone of 2,225&nbsp;Hz and a space tone of 2,025&nbsp;Hz.

Although original Bell 103 modems are no longer in common use, this encoding scheme is referred to generically as "Bell 103 modulation", and any device employing it as "Bell 103-compatible" or "a Bell 103 modem".

For many years, higher-speed modems retained the ability to emulate the Bell 103, allowing a fallback method for data to be communicated at low speed if channel conditions deteriorated.