Content deleted Content added
m →Top: add lk |
m →Top: add lk |
||
Line 10:
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 [[Antenna (radio)|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.
A '''modulator''' is a device or [[electric circuit|circuit]] that performs modulation. A '''demodulator''' (sometimes ''[[detector (radio)|detector]]'') is a circuit that performs [[demodulation]], the inverse of modulation. A [[modem]] (from '''mod'''ulator–'''dem'''odulator), used in bidirectional communication, can perform both operations. The lower frequency band occupied by the modulation signal is called the ''[[baseband]]'', while the higher frequency band occupied by the modulated carrier is called the ''[[passband]]''.{{Citation needed|date=March 2023}}
| |||