![]() Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal).Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal).Angle modulation, which is approximately constant envelope.Vestigial sideband modulation (VSB, or VSB-AM).Single-sideband modulation suppressed carrier modulation (SSB-SC).Single-sideband modulation with carrier (SSB-WC).Single-sideband modulation (SSB, or SSB-AM).Double-sideband reduced carrier transmission (DSB-RC).Double-sideband suppressed-carrier transmission (DSB-SC).Double-sideband modulation with carrier (DSB-WC) (used on the AM radio broadcasting band).Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal).Common analog modulation techniques include: In analog modulation, the modulation is applied continuously in response to the analog information signal. Several strong sidebands are apparent in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. A more complicated digital modulation method that employs multiple carriers, orthogonal frequency-division multiplexing (OFDM), is used in WiFi networks, digital radio stations and digital cable television transmission.Ī carrier, frequency modulated by a 1,000 Hz sinusoid. This alphabet can consist of a set of real or complex numbers, or sequences, like oscillations of different frequencies, so-called frequency-shift keying (FSK) modulation. More recent systems use digital modulation, which impresses a digital signal consisting of a sequence of binary digits (bits), a bitstream, on the carrier, by means of mapping bits to elements from a discrete alphabet to be transmitted. These were the earliest types of modulation, and are used to transmit an audio signal representing sound, in AM and FM radio broadcasting. Examples are amplitude modulation (AM) in which the amplitude (strength) of the carrier wave is varied by the modulation signal, and frequency modulation (FM) in which the frequency of the carrier wave is varied by the modulation signal. In analog modulation an analog modulation signal is impressed on the carrier. The frequency band occupied by the modulation signal is called the baseband, while the higher frequency band occupied by the modulated carrier is called the passband. 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). Higher frequency signals can transmit over longer distances. The carrier is higher in frequency than the modulation signal. 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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