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The term Nyquist rate is also used in a different context with units of symbols per second, which is actually the field in which Harry Nyquist was working. In that context it is an upper bound for the symbol rate across a bandwidth-limited baseband channel such as a telegraph line [ 2 ] or passband channel such as a limited radio frequency band ...
In particular, Nyquist determined that the number of independent pulses that could be put through a telegraph channel per unit time is limited to twice the bandwidth of the channel, and published his results in the papers Certain factors affecting telegraph speed (1924) [6] and Certain topics in Telegraph Transmission Theory (1928). [7]
Early uses of the term Nyquist frequency, such as those cited above, are all consistent with the definition presented in this article.Some later publications, including some respectable textbooks, call twice the signal bandwidth the Nyquist frequency; [6] [7] this is a distinctly minority usage, and the frequency at twice the signal bandwidth is otherwise commonly referred to as the Nyquist rate.
The sampling theorem was implied by the work of Harry Nyquist in 1928, [11] in which he showed that up to independent pulse samples could be sent through a system of bandwidth ; but he did not explicitly consider the problem of sampling and reconstruction of continuous signals.
The Rayleigh bandwidth of a simple radar pulse is defined as the inverse of its duration. For example, a one-microsecond pulse has a Rayleigh bandwidth of one megahertz. [1] The essential bandwidth is defined as the portion of a signal spectrum in the frequency domain which contains most of the energy of the signal. [2]
This result was presented by Claude Shannon in 1948 and was based in part on earlier work and ideas of Harry Nyquist and Ralph Hartley. The Shannon limit or Shannon capacity of a communication channel refers to the maximum rate of error-free data that can theoretically be transferred over the channel if the link is subject to random data ...
is a (suitably chosen) measure of bandwidth (in hertz), and T D {\displaystyle T_{D}} is a (suitably chosen) measure of time duration (in seconds). In time–frequency analysis , these limits are known as the Gabor limit , and are interpreted as a limit on the simultaneous time–frequency resolution one may achieve.
In 1928, John B. Johnson discovered and Harry Nyquist explained Johnson–Nyquist noise. With no applied current, the mean-square voltage depends on the resistance R {\displaystyle R} , k B T {\displaystyle k_{\rm {B}}T} , and the bandwidth Δ ν {\displaystyle \Delta \nu } over which the voltage is measured: [ 4 ]