Carrier wave
From Free net encyclopedia
A carrier wave, or carrier is a waveform (usually sinusoidal) that is modulated (modified) to represent the information to be transmitted. This carrier wave is usually of much higher frequency than the modulating signal (the signal which contains the information).
Image:Sine Cosine Graph.png Carrier waves are used when transmitting radio signals to a radio receiver.
- Frequency modulation (FM) and amplitude modulation (AM) signals are both transmitted with the help of carrier waves.
- In the case of single-sideband modulation (SSB) the carrier is suppressed (and in some forms of SSB eliminated). The carrier must be reintroduced at the receiver by a beat frequency oscillator (BFO).
The frequency for given radio station is actually the carrier wave's center frequency.
CW emission: less used by modern modulation systems
Newer forms of radio communication, such as spread spectrum and ultra wide band, do not transmit a conventional carrier wave, nor does the European standard for HDTV, known as COFDM.
- COFDM should be thought of as an array of symmetrical carrier waves. The rules governing carrier wave propagation affect COFDM differently than 8VSB.
- Some forms of spread spectrum transmission and most forms of ultra wide band transmission are mathmatically defined as being devoid of carrier waves.
- The U.S. HDTV broadcast standard, 8VSB, does include a carrier, but at much lower relative power levels than the older NTSC standard.
In telecommunication, the term carrier (cxr) or carrier wave has the following meanings:
- A waveform suitable for modulation by an information-bearing signal.
- An unmodulated emission. Note: The carrier is usually a sinusoidal wave or a uniform or predictable series of pulses. Synonym: carrier wave. <p>
- Sometimes employed as a synonym for a carrier system, or a synonym for a telecommunications provider company (operator), such as a common carrier.
Source: mostly from Federal Standard 1037C and from MIL-STD-188
da:Bærebølge
de:Trägerwelle es:Onda portadora fr:Porteuse id:Gelombang pembawa he:גל נושא nl:Draaggolf pt:Portadora
zh:载波