A new microwave synthesis chain for the primary frequency standard NIST-F1

We present the design and measurements of the microwave synthesis chain presently used in NIST-F1, the laser-cooled cesium fountain primary frequency standard in operation at NIST, Boulder, CO. The chain has been used in two accuracy evaluations of NIST-F1 (January 2005 and July 2005), each of which had a combined (type A and type B) fractional frequency uncertainty of ~ 0.5 times 10
^-15
. Additionally, this synthesis chain was in use during a recent calibration of the
¹⁹⁹
Hg
⁺
optical clock transition against Cs, which had a fractional uncertainty of 9.1 times 10
^-16