Signal modulation: Difference between revisions

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In [[electronics]] and [[telecommunications]], '''modulation''' is the process of varying one or more properties of a periodic [[waveform]], called the ''[[carrier signal]]'', with a separate signal called the ''modulation signal'' that typically contains information to be transmitted.<ref>{{Cite web |date=2014-10-22 |title=How does modulation work? {{!}} Tait Radio Academy |url=https://www.taitradioacademy.com/topic/how-does-modulation-work-1-1/ |access-date=2024-06-17 |website=Tait Radio Academy}}</ref> For example, the modulation signal might be an [[audio signal]] representing [[sound]] from a [[microphone]], a [[video signal]] representing moving images from a [[video camera]], or a [[digital signal]] representing a sequence of binary digits, a [[bitstream]] from a computer.

This carrier wave usually has a much higher [[frequency]] than the message signal does. This is because it is impractical to transmit signals with low frequencies. Generally, to receive a [[radio wave]] one needs a [[radio antenna]] with length that is one-fourth of wavelength.<ref>{{cite web |url=https://www.wimo.com/en/faq/post/what-antenna-length-do-i-need-for-which-frequency |title=General Antennas: What antenna length do I need for which frequency? |first=Rodrigo "Rod" |last=Herrera |date=April 23, 2024 |website=wimo.com |access-date=June 19, 2024 |lang=en}}</ref> For low frequency radio waves, wavelength is on the scale of kilometers and building such a large antenna is not practical. In [[radio communication]], the modulated carrier is transmitted through space as a [[radio wave]] to a [[radio receiver]].

Another purpose of modulation is to transmit multiple [[Communication channel|channels]] of information through a single [[transmission medium|communication medium]], using [[frequency-division multiplexing]] (FDM). For example, in [[cable television]] (which uses FDM), many carrier signals, each modulated with a different [[television channel]], are transported through a single cable to customers. Since each carrier occupies a different frequency, the channels do not interfere with each other. At the destination end, the carrier signal is [[demodulation|demodulated]] to extract the information bearing modulation signal.