Editing Frequency standard

{{Short description|Stable oscillator used for frequency calibration or reference}}
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[[Image:Early NBS crystal oscillator frequency standards.jpg|thumb|These precision 100 kHz [[crystal oven|oven controlled crystal oscillators]] at the US Bureau of Standards (now [[National Institute of Standards and Technology|NIST]]) served as the frequency standard for the United States in 1929.]]

A '''frequency standard''' is a stable [[electronic oscillator|oscillator]] used for [[frequency]] [[calibration]] or reference. A frequency standard generates a [[fundamental frequency]] with a high degree of [[accuracy and precision]]. Harmonics of this fundamental frequency are used to provide reference points.

Since time is the reciprocal of frequency, it is relatively easy to derive a [[time standard]] from a frequency standard. A standard clock comprises a frequency standard, a device to count off the cycles of the oscillation emitted by the frequency standard, and a means of displaying or outputting the result.

Frequency standards in a [[telecommunications network|network]] or [[Telecommunications facility|facility]] are sometimes administratively designated as ''primary'' or ''secondary''. The terms ''primary'' and ''secondary'', as used in this context, should not be confused with the respective technical meanings of these words in the discipline of [[precise time]] and frequency.

==Frequency reference==
A '''frequency reference''' is an instrument used for providing a stable frequency of some kind. There are different sorts of frequency references, [[acoustics|acoustic]] ones such as [[tuning fork]]s but also electrical ones that emit a signal of a certain frequency (a frequency standard).

Among the most stable frequency references in the world are [[caesium standard]]s (including [[atomic fountain|caesium fountain]]s) and [[hydrogen maser]]s. Caesium standards are widely recognized as having better long-term stability, whereas hydrogen masers can attain superior short-term performance; therefore, several national [[Measurement standards laboratory|standards laboratories]] use ensembles of caesium standards and hydrogen masers in order to combine the best attributes of both.

The carrier of [[time signal]] transmitters, [[Loran-C]] transmitters and of several [[longwave|long wave]] and [[mediumwave|medium wave]] broadcasting stations is derived from an [[atomic clock]] and can be therefore used as frequency standard.

==See also==
* [[Rubidium standard]]
* [[Standard frequency and time signal service]]

==References==
{{Reflist}}

{{DEFAULTSORT:Frequency Standard}}
[[Category:Electronics standards]]
[[Category:Frequency]]