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'''Bandwidth-அலைவரிசைப்பட்டை அகலம்'''
'''Bandwidth''' is a measure of [[frequency]] range and is typically measured in [[hertz]].
Bandwidth is a central concept in many fields, including [[information theory]], [[radio]] [[communication]]s, [[signal processing]], and [[spectroscopy]]. Bandwidth also refers to data rates when communicating over certain media or devices.
ஒப்புமைக் குரல் சமிக்ஞை, ஒரு தனிப்பட்ட அதிர்வெண் மட்டும் கொண்டு திகழ்வதில்லை; தொடர்பாடல் தடத்தில் உள்ள பலவேறுபட்ட அதிர்வெண்கள் கொண்ட அலைவடிவத்தால் ஆனது. அதிர்வெண்களின் ஒரு குறிப்பிட்ட கூட்டுக் கலவைதான் ஒருவருடைய குரலை நிர்ணயிக்கின்றது. இயற்கையின் பல படைப்புகளும் நிகழ்வுகளும் பலதரப்பட்ட அதிர்வெண்களின் கூட்டுக் கலவைகளாக வெளிப்படுகின்றன. வானவில்லின் வண்ணங்கள் பல்வேறு ஒளி அதிர்வெண்களின் சேர்க்கையே; இசையொலியும் பல்வேறு கேட்பொலி அதிர்வெண்களாலானதே. சமிக்ஞைகளில் உள்ள அதிர்வெண்களின் அளவெல்லையைக் குறிப்பது, தொடர்பாடல் களத்தில் உள்ள வழக்கம். இதை அலைவரிசைப் பட்டை அகலம் என்று வழங்குவர்.
== Explanation ==
Bandwidth is a key concept in many applications. In [[radio]] communications, for example, bandwidth is the range of frequencies occupied by a [[modulated]] [[carrier wave]], whereas in [[optics]] it is the width of an individual [[spectral line]] or the entire [[electromagnetic spectrum|spectral range]]
எ-டு: தொலைபேசியில் பேச்சுச் சமிக்ஞையின் அலைப்பட்டை, 200 Hz-3500 Hz வரை எல்லைப்படுத்தப்பட்டுள்ளது.
There is no ''single'' universal precise definition of bandwidth, as it is vaguely understood to be a measure
of how wide a function is in the [[frequency domain]].
[[பகுப்பு:குறிப்பலைப் பதப்படுத்தல்]]
For different applications there are different precise definitions. For example, one definition of bandwidth could be the range of frequencies beyond which the frequency function is zero. This would correspond to the mathematical notion of the support of a function (i.e., the total "length" of values for which the function is nonzero).
Another definition might not be so strict and ignore the frequencies where the frequency function is ''small''. Small could mean less than 3 [[decibel|dB]] below (i.e., less than half of) the maximum value, or it could mean below a certain absolute value. As with any definition of the ''width'' of a function, there are many definitions available, which are suitable for different applications.
According to the [[Shannon–Hartley theorem]], the data rate of reliable communication is directly proportional to the frequency range of the signal used for the communication. In this context, the word bandwidth can refer to either the data rate or the frequency range of the communication system (or both).
== Analog systems ==
[[Image:bandwidth.png|right|300px|thumb|Illustration of the concept of 3-dB bandwidth, or half-power bandwidth. The vertical axis here is proportional to power (square of Fourier magnitude); the frequency axis of this symbolic diagram can be linear or [[logarithm]]ically scaled.]]
For [[analog signal]]s, which can be mathematically viewed as a functions of time, '''bandwidth''' is the width, measured in [[hertz]], of a frequency range in which the signal's [[Fourier transform]] is nonzero. This definition can be relaxed where the bandwidth would cover the range of frequencies where the signal's Fourier transform has a power above a certain amplitude threshold, say 3 dB below the maximum value, in the frequency domain. Bandwidth of a signal is a measure of how rapidly its parameters (e.g. amplitude and phase) fluctuate with respect to time. Hence, the greater the bandwidth, the faster the variation in the signal parameters may be. The word
bandwidth applies to signals as described above, but it could also apply to ''systems''. In the latter case, to say
that a system has a certain bandwidth means that the system can process signals of that bandwidth.
A [[baseband]] bandwidth is a specification of only the highest frequency limit of a signal. A non-baseband bandwidth is a difference between highest and lowest frequencies.
As an example, the (non-baseband) 3-dB bandwidth of the function depicted in the figure is <math>f_2-f_1</math>, whereas other definitions of bandwidth would yield a different answer.
A commonly used quantity is ''fractional bandwidth''. This is the bandwidth of a device divided by its center frequency. E.g., a device that has a bandwidth of 2 MHz with center frequency 10 MHz will have a fractional bandwidth of 2/10, or 20%.
The fact that [[real numbers|real]] [[baseband]] systems have both negative and positive frequencies can lead to confusion about bandwidth, since they are sometimes referred to only by the positive half, and one will occasionally see expressions such as <math>B = 2W</math>, where <math>B</math> is the total bandwidth, and <math>W</math> is the positive bandwidth. For instance, this signal would require a [[lowpass filter]] with cutoff frequency of at least <math>W</math> to stay intact.
The 3-dB bandwidth of an [[electronic filter]] is the part of the filter's frequency response that lies within 3 dB of the response at its peak, which is typically at or near its [[center frequency]].
In signal processing and [[control theory]] the bandwidth is the frequency at which the [[closed-loop]] system gain drops to −3 dB.
In basic electric circuit theory when studying Band-pass and Band-reject filters the bandwidth represents the distance between the two points in the frequency domain where the signal is <math>\frac{1}{\sqrt{2}}</math> of the maximum signal amplitude (half power).
In photonics, the term bandwidth occurs in a variety of meanings:
*the bandwidth of the output of some light source, e.g., an ASE source or a laser; the bandwidth of ultrashort optical pulses can be particularly large
*the width of the frequency range that can be transmitted by some element, e.g. an optical fiber
*the gain bandwidth of an optical amplifier
*the width of the range of some other phenomenon (e.g., a reflection, the phase matching of a nonlinear process, or some resonance)
*the maximum modulation frequency (or range of modulation frequencies) of an optical modulator
*the range of frequencies in which some measurement apparatus (e.g., a powermeter) can operate
*the data rate (e.g., in Gbit/s) achieved in an optical communication system
===See also===
*[[Narrowband]]
*[[Broadband]]
*[[Modulation]]
== Digital systems ==
In a digital communication system, bandwidth has a dual meaning. In the technical sense, it is slang for [[baud]], the rate at which symbols may be transmitted through the system. It is also used in the colloquial sense to describe [[channel capacity]], the rate at which bits may be transmitted through the system (see [[Shannon Limit]]). Hence, a 66 MHz [[digital]] [[data bus]] with 32 separate data lines may properly be said to have a bandwidth of 66 MHz and a capacity of 2.1 Gbit/s — but it would not be surprising to hear such a bus described as having a "bandwidth of 2.1 Gbit/s." Similar confusion exists for analog [[modem]]s, where each symbol carries multiple bits of information so that a modem may transmit 56 kbit/s of information over a [[phone line]] with a bandwidth of only 12 kHz.
In [[discrete time system]]s and [[digital signal processing]], bandwidth is related to [[sampling rate]] according to the [[Nyquist-Shannon sampling theorem]].
''Bandwidth'' is also used in the sense of [[commodity]], referring to something limited or something costing money. Thus, communication costs bandwidth, and improper use of someone else's bandwidth may be called [[bandwidth theft]].
== Meaning of bandwidth in web hosting ==
In website hosting, bandwidth is the amount of information downloadable from the webserver over a prescribed period of time. In essence, it is the rate [data/time], but the time in this case is not seconds but rather a month or a week. So this rate is not like 56K or broadband, etc., which are also bandwidth but are measured per second. Web hosting companies often quote a monthly [[Bandwidth cap|bandwidth limit]] for a website, for example 100 GB/month. If visitors to the website download a total greater than 100 GB in one month, the bandwidth limit will have been exceeded.
==See also==
*[[Bandwidth extension]] ▼*[[Shannon–Hartley theorem]]
*[[List of device bandwidths]]
*[[Latency vs Bandwidth]] ▼*[[Bandwidth theft]]
*[[Bandwidth cap]]
*[[Throughput]]
*[[Measuring data throughput]]
*[[Bandwidth Controller]]
*[[Data rate]]
[[Category:Signal processing]]
[[Category:Filter theory]]
[[Category:Information theory]]
[[ca:Ample de banda]]
[[da:Båndbredde (signalbehandling)]]
[[de:Bandbreite]]
▲*[[ en:Bandwidth extension]]
[[es:Ancho de banda]]
[[fr:Bande passante]]
▲*[[ Latency vs id:Bandwidth]]
[[it: LarghezzaAmpiezza di banda]] ▼[[ko:대역폭]]
[[id:Bandwidth]]
▲[[it:Larghezza di banda]]
[[nl:Bandbreedte]]
[[no:Båndbredde]]
[[sl:Pasovna širina]]
[[sr:Ширина фреквенцијског појаса]]
[[sv:Bandbredd]]
[[ta:அலையெண் கற்றையகலம்]]
[[zh:带宽]]
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