Analog Modulation:
The process of transmitting an analog baseband (low frequency) signal, such as an audio or television signal, over a higher frequency signal such as a radio frequency band. Analogue modulation is the basis of modulation operations. Or we can say that it is a change of one of the properties of the high-frequency current wave (amplitude of oscillation - frequency of oscillation - phase of oscillation),
so there are three types of analog modulation are as follows:
Amplitude Modulation AM:
In the process of capacitive modulation (A.M.), the amplitude of the radio wave (carrier) is changed by the effect of the portable wave, as we get a fixed-frequency radio wave with variable amplitudes, so that the changes in the carrier amplitude correspond to the frequency of the portable wave. The embedded radio wave envelope represents two audio waves carried on the radio wave. This technique is based on changing the value of the amplitude of the carrier signal as a linear function with the value of the transmitted signal (basic), and this actually means the process of multiplying the carrier signal by the modulation signal and it is characterized by its ease of design and ease of de-modulation, but the inclusion of the amplitude makes the signal highly susceptible to noise and sometimes it is lost if it is not The transmission signal is strong enough.
Frequency Modulation FM:
Electromagnetic radio waves may interfere with different random sources, such as thunderstorms, electrical machines, or others, which affect the amplitude of the wave in the form of noise, which causes one of the problems faced by the capacitive modulation method, so the carrier frequency is changed according to the wave or the audio signal while the amplitude of the wave remains The carrier is fixed and the resulting wave is called a frequency modulated wave.
The precise definition of this modulation is a technique of encoding information on a specific signal, whether analog or digital, by changing the carrier frequency according to the frequency of the modulated signal. The modulated signal is nothing but information or a message that must be transmitted after it is converted into an electronic signal. FM modulation works on changing the frequency of the carrier signal while keeping its amplitude constant in proportion to the modulating signal. portable
Phase Modulation PM:
In this type of modulation, the angle or phase of the carrier frequency signal changes linearly with the value of the basic signal, and this type reconciles the two previous modulation types. This is why the signal is distinguished by the quality of the signal because the frequency of the wave is less than the frequency used in the frequency modulation, but what is disadvantaged is the difficulty of obtaining the necessary equipment to configure it, although these The technology bears the advantages of frequency modulation in a lower bandwidth than its predecessor, but the problem lies in the complexity of the devices in both modulation and demodulation, which limits their applications.
Please check :
Introduction to Signals Modulation Part 1
Modulating process role in communication systems Part 2
