Bell 202 modem: Difference between revisions
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==See also== |
==See also== |
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* [[Caller ID]] |
* [[Caller ID]] |
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* [http://www.arrl.org/tis/info/pdf/49244.pdf Getting Started in Digital Communications - Packet (PDF)] |
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==External links== |
==External links== |
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Revision as of 11:42, 15 June 2009
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The Bell 202 modem was an early modem developed by AT&T. It used audio frequency-shift keying to encode and transfer data at a rate of 1200 bits per second, half-duplex (one-way). This signalling protocol, also used in third-party modems, is referred to generically as Bell 202 modulation, and any device employing it as Bell-202-compatible.
- Bell 202 uses a 1200 Hz tone for mark (typically a binary 1) and 2200 Hz for space (typically a binary 0).
In North America (and perhaps elsewhere), Bell 202 modulation is used to transmit Caller ID information over POTS lines in the public telephone network. It is also employed in some commercial settings.
Surplus Bell 202 modems were used by amateur radio operators to construct the first packet radio stations, and despite its low signalling speed, Bell 202 modulation remains the standard for amateur VHF operation in most areas. Notably, Automatic Position Reporting System transmissions are most often encoded this way.
Related technology
The ITU-T V.23 communications standard defines a similar modulation scheme.