本地異步通信技術rs-232-文庫吧在線文庫
【正文】 he carrier oscillates continuously, even when no data is being sent. To send data, a transmitter modifies the carrier slightly. Such modification are called modulation(調(diào)制 ). The transmitter generates a continuously oscillating carrier signal, which it modulates according to the data being sent. The receiver on a longdistance munication link must be configured to recognize the carrier that the sender uses. The receiver monitors the ining carrier, detects modulation , reconstructs the original data, and discards the carrier. Network technologies use a variety of modulation techniques, including： amplitude modulation (AM調(diào)幅 ), frequency modulation (FM調(diào)頻 ), phase shift modulation (PM調(diào)相 ). Modem Hardware Used For Modulation And Demodulation A hardware circuit that accepts a sequence of data bits and applies modulation to a carrier wave according to the bits is called a modulator(調(diào)制器 ). A hardware circuit that accepts a modulated carrier wave and recreates the sequence of data bits that was used to modulate the carrier is called a demodulator(解調(diào)器 ). ? Transmission of data across a long distance requires a modulator at one end of the transmission line and a demodulator at the other. ? Most work systems are full duplex, each location needs both a modulator and a demodulato
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