| 单词 | modem (modulator/demodulator) |
| 释义 | modem (modulator/demodulator) 1. A device that comprises both a modulator that changes a sig- nal in some way in the forward direction and a demodulator that changes the signal back to its original form in the backward direction, essentially reversing the modulation process. Modems operate in balanced and symmetrical pairs, with one at each end of the communications circuit and with both having the same capabilities, at least at a minimum level.There are many types of devices characterized as modems, including cable modems, conventional modems, ADSL modems, ISDN modems (terminal adapters, or TAs), line drivers, and short haul modems. See also ADSL, cable modem, line driver, short haul modem, and TA. 2. A conventional modem is a signal conversion device that interfaces a digital device to an analog circuit or channel. On the transmit side of the connection, a modem accepts an incoming digital signal and modulates (i.e., changes or varies) the characteristics of an electromagnetic waveform in some way to represent that signal over an analog carrier. The modulation technique generally involves amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), or some combination. On the receive side of the connection, a modem with matching capabilities accepts the modulated signal over the analog carrier and demodulates the signal to extract the information and recreate the original digital signal. Many modems are capable of operating in full duplex, simultaneously modulating signals as they transmit them and demodulating signals as they receive them. See also AM, FM, and PM. |
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