Bell 103 modem

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 computers, released by AT&T Corporation in 1963.[1][2] It allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 300 bits per second. It followed the introduction of the 110 baud 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 Hz and a space tone of 1,070 Hz.
  • The answering station used a mark tone of 2,225 Hz and a space tone of 2,025 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.

  1. ^ Peter Ha (25 October 2010). "All-TIME 100 Gadgets: Bell 103". Retrieved 28 August 2023.
  2. ^ Joseph J. Antinori (July 1989). "From Morse to Modems: A Brief History of Telecommunications". PC Magazine. p. 209.