Why is modulation necessary?Is it because the message signal has a very low frequency so it can get easily attenuated in the channel so it is mounted on a high frequency carrier,or is it because carrier waves have a large wavelength so they can travel longer distances,or is it both?

Modulation has various applications including the two you mentioned. The two which you mentioned are also right. Its purpose is also to transform the signals (messages) in the way that they suits the transmission or a common career signals such that various different messages can be transmitted through a common career. Thanks and Regards, Pratik Tibrewal askiitians faculty, BTech IITG

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