Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Operation of the NIST-F1 Cesium Fountain Primary Frequency Standard with a Maser Ensemble



Thomas E. Parker, Steven R. Jefferts, Thomas P. Heavner, Elizabeth A. Donley


The operation of a caesium fountain primary frequency standard is greatly influenced by the characteristics of two other important capabilities. The first is a stable frequency reference and the second is the frequency-transfer system. A stable frequency reference such as a hydrogen maser is a virtual necessity since essentially no fountain dead time can be tolerated without it. The frequency stability of this reference has a significant impact on the procedures for evaluating certain systematic biases in the fountain. State-of-the-art frequency transfer technology also is necessary if the fountain is intended to contribute to TAI, or to be compared to other remotely located frequency standards without excessive degradation of stated uncertainties. We discuss the facilities available at the National Institute of Standards and Technology and how they impact the operation of NIST-F1, the primary frequency standard at NIST.


cesium fountain, dead time, hydrogen maser, time transfer


Parker, T. , Jefferts, S. , Heavner, T. and Donley, E. (2005), Operation of the NIST-F1 Cesium Fountain Primary Frequency Standard with a Maser Ensemble, Metrologia, [online], (Accessed April 23, 2024)
Created September 13, 2005, Updated February 17, 2017