| 摘要 |
A narrow band modem for communicating with a remote modem may include a narrow band demodulator for demodulating digital data from the remote modem and a narrow band modulator for modulating digital data for transmission to the remote modem. In particular, the narrow band modulator may include an input for receiving digital data to be modulated, a level mapper for mapping the digital data to at least one of a plurality of different levels, and a carrier generator for generating a carrier at a predetermined frequency. In addition, the narrow band modulator may also include a counter for generating a gating control signal every predetermined number of cycles of the carrier, and a gating device outputting the level from the level mapper for a predetermined portion of a carrier cycle responsive to the gating control signal, and for outputting the carrier otherwise.
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