Bell 103 modem

The Bell 103 modem was the first commercial modem for computers, released by AT&T in 1962. It allowed digital data to be transmitted over regular telephone lines at a speed of 300 bits per second.

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.

Applications

Bell 103 modulation is still in use today, in shortwave radio, amateur radio, and some commercial applications. Its low signalling speed and use of audio frequencies makes it suitable for noisy or unreliable narrowband links.

For example, the CHU shortwave station in Ottawa, Canada transmits a Bell 103-compatible digital time code every minute. Bell 103 modulation is also the standard for amateur packet radio in the HF (shortwave) bands.

Related technology

The ITU-T V.21 communications standard defines a very similar modulation scheme. Commercial 300 baud modems typically support both formats.

ee also

*List of device bandwidths


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • modem — /moh deuhm, dem/, Computers. n. 1. an electronic device that makes possible the transmission of data to or from a computer via telephone or other communication lines. v.t. 2. to send or receive (information, data, or the like) via a modem.… …   Universalium

  • Modem — For other uses, see Modem (disambiguation). A modem (modulator demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The… …   Wikipedia

  • Modem standards — The CCITT, an international committee that specifies the way modems and fax machines transmit information to ensure compatibility among modems, has classified dial up modems according to the following modulation standards:* Bell 103M 212A: Older… …   Wikipedia

  • List of modem standards — The CCITT, an international committee that specifies the way modems and fax machines transmit information to ensure compatibility among modems, has classified dial up modems according to the following modulation standards: Bell 103M 212A: Older… …   Wikipedia

  • telecommunication — [tel΄ə kə myo͞o΄ni kā′shən] n. [also pl., with sing. or pl. v.] communication by electronic or electric means, as through radio, telephone, telegraph, television, or computers * * * tel·e·com·mu·ni·ca·tion (tĕlʹĭ kə myo͞o nĭ kāʹshən) n. 1. The… …   Universalium

  • Telegraphy — (from the Greek words (τηλε) = far and (γραφειν) = write) is the long distance transmission of written messages without physical transport of letters. Radiotelegraphy or wireless telegraphy transmits messages using radio. Telegraphy includes… …   Wikipedia

  • Actrix (computer) — The Actrix computer, released in 1984 by Actrix Computer Corporation, was a Zilog Z80 based transportable personal computer running CP/M 80 V2.2. Its predecessor was the Access Computer computer by Access Matrix Computer Corporation.… …   Wikipedia

  • Novation CAT — The original Novation CAT Novation was an early modem manufacturer whose CAT series were popular in the early home computer market in the late 1970s and early 1980s, notably on the Apple II. The Hayes Smartmodem 300, introduced in 1981, helped… …   Wikipedia

  • Hayes Microcomputer Products — was a U.S. based manufacturer of modems. They are particularly well known for their Smartmodem, which introduced the ability to control the modem through commands sent in the data stream itself. The smart modem approach dramatically simplified… …   Wikipedia

  • List of device bit rates — This is a list of device bit rates, or physical layer information rates, net bit rates, useful bit rates, peak bit rates or digital bandwidth capacity, at which digital interfaces of computer peripheral equipment and network devices can… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.