The transfer of information or message using electronic devices in the form of electronic signals from one point to another is called electronic communication. Electronic communication uses transmitter, transmission channel and receiver as its basic components for the transfer of information between two points. The message signal to be sent has different range of frequencies depending on the nature of information to be transferred. The type of communication system needed for a given signal depends on the essential band of frequencies known as bandwidth of the signal. On the basis of signal used, communication system is classified into two important forms i.e., digital and analog communication system. Any communication system requires a permissible range of frequencies for satisfactory transmission of the information contained in the signal. The referred band of frequency is called bandwidth of the system. The propagation of electromagnetic waves depends on the path they follow and hence its strength decreases as it moves away from the transmitter. Considering the frequency range, the waves are categorised as ground waves, sky waves and space waves. The signals having low frequencies cannot be transmitted to long distances and therefore, they are superimposed on a high frequency carrier signal by a process called modulation. On modulating a carrier signal, its characteristics vary in accordance with the message signal. The resulting wave can be amplitude modulated, frequency modulated or pulse modulated depending on the nature of variation in the characteristic of the wave. An amplitude modulated wave is produced by applying both the message signal and carrier wave to a non linear device followed by a band pass filter. This amplitude modulated wave form is recovered by a process called AM detection. It is done using a rectifier and an envelope detector.
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