Bell 202 modem: Difference between revisions
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{{Unreferenced|date=March 2009}} |
{{Unreferenced|date=March 2009}} |
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The '''Bell 202 modem''' was an early [[modem]] developed by [[AT&T]]. It |
The '''Bell 202 modem''' was an early [[modem]] developed by [[AT&T]]. It specifies [[frequency-shift keying|audio frequency-shift keying]] (AFSK) to encode and transfer data at a rate of 1200 [[bits per second]], [[Duplex (telecommunications)#Half-duplex|half-duplex]] (one-way) and at a rate of 1800 bits per second [[Duplex (telecommunications)#Full-duplex|full duplex]] using DPSK modulation. 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''. |
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* Bell 202 uses a 1200 Hz tone for ''mark'' (typically a binary ''1'') and 2200 Hz for ''space'' (typically a binary ''0''). |
* Bell 202 uses a 1200 Hz tone for ''mark'' (typically a binary ''1'') and 2200 Hz for ''space'' (typically a binary ''0''). |
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In [[North America]] (and perhaps elsewhere), Bell 202 modulation is used to transmit [[Caller ID]] information over [[Plain_old_telephone_service|POTS lines]] in the [[Public Switched Telephone Network|public telephone network]]. It is also employed in some commercial settings. |
In [[North America]] (and perhaps elsewhere), Bell 202 modulation is used to transmit [[Caller ID]] information over [[Plain_old_telephone_service|POTS lines]] in the [[Public Switched Telephone Network|public telephone network]]. It is also employed in some commercial settings. |
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Surplus Bell 202 modems were used by [[amateur radio]] operators to construct the first [[packet radio]] stations, |
Surplus Bell 202 modems were used by [[amateur radio]] operators to construct the first [[packet radio]] stations, despite its low [[data signaling rate|signalling speed]]. The modified Bell 202 modulation, '''[[AX.25]]''', remains the standard for amateur [[VHF]] operation in most areas. Notably, [[Automatic Packet Reporting System]] (APRS) transmissions are encoded this way on VHF. On [[HF]], APRS uses [[Bell 103 modem]] tones. |
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==Related technology== |
==Related technology== |
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Revision as of 12:24, 15 June 2009
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The Bell 202 modem was an early modem developed by AT&T. It specifies audio frequency-shift keying (AFSK) to encode and transfer data at a rate of 1200 bits per second, half-duplex (one-way) and at a rate of 1800 bits per second full duplex using DPSK modulation. 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, despite its low signalling speed. The modified Bell 202 modulation, AX.25, remains the standard for amateur VHF operation in most areas. Notably, Automatic Packet Reporting System (APRS) transmissions are encoded this way on VHF. On HF, APRS uses Bell 103 modem tones.
Related technology
The ITU-T V.23 communications standard defines a similar modulation scheme.