which modulation is best in audio and video system positive or negative and why?..
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When audio signals are transmitted through thousands of miles through radio transmission, audio frequencies that are within the frequency range of 15 Hertz to 20 KiloHertz have very small signal strength and therefore Can not be transmitted through the antenna for communication purposes. The radiation of electrical energy is only possible at frequencies above 20 KiloHertz. The main advantage of high frequency signals is that they can be transmitted over very long distances dissipating very small energy. Therefore, the audio signals must be sent together with the high frequency signals for communication. This can be done by superimposing electrical audio signals on a high frequency wave called the carrier wave. The carrier wave is generated from radio frequency oscillators and is not amortized in nature. Thus, when the audio signal is superimposed on a carrier wave, the resulting wave obtains all the characteristics of the audio signal. The method of superimposing an audio signal on the carrier wave is called modulation.
The best way to define the modulation is:
The process of printing low-frequency information that is transmitted to a high-frequency wave, called the carrier wave, changing the characteristics of its amplitude, frequency or phase angle is called modulation.
Another definition for modulation is:
The process of altering the characteristics of the amplitude, frequency or phase angle of the high frequency signal according to the instantaneous value of the modulation wave is called modulation.