Modulation
Modulation is changing the frequency, amplitude, phase, or pulse width of a wave to transmit data in digital form. Signals consist of two components, the information signal and the carrier signal. The transmission of any signal over some communication medium usually involves modulation of a carrier. Prior to their transmission the information signal and the carrier signal are combined. The process of combining the information signal with the career signal is called modulation.
Before being modulated by an information signal, the carrier signal has a single FREQUENCY and a steady amplitude. After modulation the carrier will have varying amplitude or frequency. There are various types of modulation. The most important modulations are:
(i) Amplitude Modulation (AM)
(ii) Frequency Modulation (FM)
(iii) Phase Modulation (PM)
(iv) Pulse Modulation
Amplitude Modulation (AM):
Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. Amplitude Modulation occurs when a voice signal’s varying voltage is applied to a carrier frequency.
Frequency Modulation (FM):
Modulation in which the amplitude of a carrier wave is varied in accordance with some characteristic of the modulating signal. Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave.
Phase Modulation (PM):
Phase modulation (PM) is a form of modulation which represents information as variations in the instantaneous phase of a carrier wave.