The transmitted information is embedded in the control (modulating) signal, and the role of the information carrier is performed by a high-frequency vibration, called the carrier (modulated). Modulation, therefore, is the process of “landing” information waveforms on a known carrier in order to obtain a new, modulated signal.
As a result of modulation, the spectrum of the low-frequency control signal is transferred to the high-frequency region. This allows, when organizing broadcasting, to adjust the operation of all transceiver devices at different frequencies so that they do not “interfere” with each other.
Demodulation is a process inverse to the modulation of oscillations, the extraction of an information (modulating) signal from a modulated high (carrier) frequency oscillation.
When transmitting signals (sound, video), low frequency voltage or current fluctuations are used to modulate (a slight change in amplitude, frequency or phase) high frequency fluctuations. At the receiving station, from these complex vibrations, using special methods, low frequency vibrations (from 20 Hz to 20 kHz) are again isolated, which, after amplification, are fed to a loudspeaker (in the case of audio signals) or a screen (in the case of video signals).
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