The main modulation function is signal transformation or transfer from low-frequency range to higher for further transfer through radio or cable carrier line. The data transferred is encoded in the control (information) signal, while the high-frequency oscillation is data carrier. Thus modulation represents the carrier transformation process with the known parameters in compliance with the rule set by the control (information) signal. The carrier can be represented by different signal forms (rectangle, triangle etc.), but the harmonic oscillations are the most frequently used (sinusoidal form). Depending on the oscillation parameter changed there are three main modulation types: amplitude, frequency and phase.
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