Modem

The word modem, a blend of "modulator" and "demodulator", refers to a device that modulates an analog "carrier" signal (such as sounds over a telephone) to encode digital information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Primarily used to communicate via telephone lines, modems can be used over any means of transmitting sound, from driven diodes to radio.

Different modulation schemes:

• Amplitude modulation
• Frequency modulation
• [Frequency-shift keying]?
• [Phase-shift keying]?
• Quadrature amplitude modulation