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A rubidium standard or rubidium atomic clock is a frequency standard in which a specified hyperfine transition of electrons in rubidium-87 atoms is used to control the output frequency. It is the most inexpensive, compact, and widely used type of atomic clock, used to control the frequency of television stations, cell phone base stations, in test equipment, and global navigation satellite systems like GPS. Commercial rubidium clocks are less accurate than cesium atomic clocks, which serve as primary frequency standards, so the rubidium clock is a secondary frequency standard. However, rubidium fountains are currently being developed that are even more stable than caesium fountain clocks.
All commercial rubidium frequency standards operate by disciplining a crystal oscillator to the rubidium hyperfine transition of 6834682610.904 Hz. The intensity of light from a rubidium discharge lamp that reaches a photodetector through a resonance cell will drop by about 0.1% when the rubidium vapor in the resonance cell is exposed to microwave power near the transition frequency. The crystal oscillator is stabilized to the rubidium transition by detecting the light dip while sweeping an RF synthesizer (referenced to the crystal) through the transition frequency.
- Stanford Research Systems documentation on the PRS10 frequency standard: http://www.thinksrs.com/downloads/PDFs/Catalog/PRS10c.pdf
- This article incorporates public domain material from the National Institute of Standards and Technology document "http://tf.nist.gov/general/enc-re.htm#resonancefrequency".
- This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
- NIST Time & Frequency A-Z Glossary - Resonance Frequency
- Secondary Representation of the SI Second
- PTB "Unit of Time"
- USNO Rubidium Fountain Project
- NPL Rubidium Fountain
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