A modem (from modulator– demodulator), used in bidirectional communication, can perform both operations. A demodulator (sometimes detector) is a circuit that performs demodulation, the inverse of modulation. At the destination end, the carrier signal is demodulated to extract the information bearing modulation signal.Ī modulator is a device or circuit that performs modulation. Since each carrier occupies a different frequency, the channels do not interfere with each other. For example, in cable television (which uses FDM), many carrier signals, each modulated with a different television channel, are transported through a single cable to customers.
In radio communication, the modulated carrier is transmitted through space as a radio wave to a radio receiver.Īnother purpose of modulation is to transmit multiple channels of information through a single communication medium, using frequency-division multiplexing (FDM). This is because it is impractical to transmit signals with low frequencies. This carrier wave usually has a much higher frequency than the message signal does. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. Categorization for signal modulation based on data and carrier types
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