Bandwidth Totally Explained

Everything about Bandwidth totally explained

ť For the term in computers, see Bandwidth (computers).

For the term in linear algebra, see Sparse matrix. Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz. In case of a baseband channel or signal, the bandwidth is equal to its upper cutoff frequency. Bandwidth in hertz is a central concept in many fields, including electronics, information theory, radio communications, signal processing, and spectroscopy.
In computer networking and other digital fields, the term bandwidth often refers to a data rate measured in bits/s, for example network throughput. The reason is that according Hartley's law, the digital data rate limit (or channel capacity) of a physical communication link is related to its bandwidth in hertz, sometimes denoted analog bandwidth. For bandwidth (computers), less ambiguous terms are, for example, gross bit rate, net bit rate, throughput, goodput or channel capacity.

Overview

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's the width of an individual spectral line or the entire spectral range.
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 (for example, the total "length" of values for which the function is nonzero). A less strict and more practically useful definition will refer to the frequencies where the frequency function is small. Small could mean less than 3 dB below (for example, less than half of) the maximum value, or more rarely 10 dB, or it could mean below a certain absolute value. As with any definition of the width of a function, many definitions are suitable for different purposes.

Analog systems

For analog signals, which can be mathematically viewed as functions of time, bandwidth BW or

Delta f

is the width, measured in hertz, of the frequency range in which the signal's Fourier transform is nonzero. Because this range of non-zero amplitude may be very broad, this definition is often relaxed so that the bandwidth is defined as the range of frequencies where the signal's Fourier transform has a power above a certain amplitude threshold, commonly half the maximum value (half power

approx -3

dB, since

10 mathrm

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, for example, 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, for example an optical fiber
the gain bandwidth of an optical amplifier
the width of the range of some other phenomenon (for example, 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 (for example, a powermeter) can operate
the data rate (for example, in Gbit/s) achieved in an optical communication system

Further Information

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