MODEM

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This is a modulator/demodulator for the transmission of computer information over telephone lines. It changes the signals into a form suitable for telephone lines. The most well- known type of instrument receives an ordinary telephone handset into two rubber cups which present acoustic information to the microphone, usually bleeping tones, and detect the tones received down the line and convert them into pulses suitable for the particular computer being used. The main limitation of this method is the slow rate at which information can be handled (usually 300 bits/s). To operate at higher speeds it is usual for the modem to be connected directly to the telephone line so that information may be transmitted as a series of electrical pulse codes, although tones are often used.