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Write three important factors that justify the need of modulating a message signal. Show diagrammatically how an amplitude modulated wave is obtained when a modulating signal is superimposed on a carrier wave.

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Hint : Modulation is defined as the process of varying one or more than one property of a wave with an additional modulating signal for data transmission. Now using this definition, justify the need of modulating the signal along with a diagram.

Complete step by step answer
Now that we know what modulation is, let us understand the necessity of signal modulation, which will help us to further understand the factors affecting modulation. Modulation allows us to send signals over a frequency range so that there won’t be a loss in the waveform. This allows waveforms to be transmitted over a larger distance from the receiver. The modulated wave will be different from the original waveform and thus needed to be demodulated to recover the original signal.
One of the examples of modulation is radio signals or even your radio sets. So considering the example of your normal radio sets, it is mandatory that all radio sets come with an antenna. Ever wondered what its purpose is? The antenna is the receiver, which receives the modulated signal sent through the air.
Now one of the factors that are essential for signal modulation is the size of the antenna. In order to get a good hold of signals from various locations, the size of the antenna should be a quarter of the wavelength.
The second factor that affects the modulation of the message signal is the effective power radiated by an antenna. For good transmission, higher power is needed, and hence there comes the requirement of higher frequency transmission.
The third factor is the interference of signals of various wavelengths from different transmitters. So in order to distinguish the signal from other signals, modulators increase the wavelength and frequency of the signals and thus help in a smooth progression.
The below diagram shows how signals are modulated.


Note
The effective power radiated by an antenna is expected to be $ \dfrac{1}{{{\lambda ^2}}} $ to obtain a good signal and the size of the antenna is expected to be $ \dfrac{\lambda }{4} $ .