Modulation is the process of changing one or more parameters of a carrier high-frequency oscillation according to the changes in the parameters of the transmitted signal.
The essence of modulation lies in varying one parameter of a high-frequency harmonic oscillation (called the carrier wave, with its frequency referred to as the carrier frequency) according to the law of a low-frequency (modulating) signal containing the transmitted message.
For long-distance transmission of signals using electromagnetic waves, it is necessary to shift the spectrum of a low-frequency signal into the high-frequency (radio frequency) range. This frequency spectrum shift is called modulation, and it is performed by a modulator. The carrier is usually a harmonic oscillation characterized by three parameters: amplitude, frequency, and phase.
If the amplitude is changed proportionally to the transmitted signal, the resulting signal is called amplitude-modulated (AM); if the frequency changes, it is called frequency-modulated (FM); if the phase changes, it is called phase-modulated (PM).
Modulation is the process of combining the information signal—in our case, an audio (modulating) signal—with the frequency of a generator (carrier frequency). Modulation alters the form of the RF oscillations in a specific way and comes in several types. In radio communication, amplitude modulation (AM) and frequency modulation (FM) are the most commonly used.
Amplitude modulation (AM) is modulation in which undamped oscillations vary in amplitude according to the lower-frequency modulating oscillations.
Frequency modulation (FM) is modulation in which the carrier frequency of the signal changes according to the modulating oscillation.
Frequency modulation has greater noise immunity compared to amplitude modulation. This is because interference at the receiver input typically causes random amplitude variations, distorting the information parameter. In frequency modulation, amplitude variations caused by noise do not affect the information parameter—frequency.
Related articles: Radio Frequency Spectrum, Types of Modulation, FM, FDMA, TDMA, dPMR, Polar Modulation, FM Frequencies in Moscow.