Rubidium Frequency Standard for the GPS IIF program and modifications for the RAFSMOD Program

• Main Authors: Dupuis, R.T., Lynch, T.J., Vaccaro, J.R.
• Format: Conference Proceeding
• Language: English
• Subjects: Clocks; Global positioning system; Physics; Stability analysis; Stability criteria; Thermal stability
• ISSN: 2327-1914
• DOI: 10.1109/FREQ.2008.4623081

PerkinElmer provides the rubidium frequency standards (RFS) for the Boeing Block IIF GPS navigation satellites. The PerkinElmer RFS-IIF is the latest generation of its high performance rubidium clocks which have performed very successfully on board the block IIR GPS space vehicles for more than 10 years.The RFS-IIF output is the traditional 10.23 MHz rather than the =13.4 MHz "natural frequency" utilized for block IIR. This necessitated the addition of a secondary phase lock loop (PLL) synthesizer to convert the Rb natural frequency to 10.23 MHz. One main design challenge was to add this new section with a minimum impact on size, weight, power, performance, radiation hardness, reliability and design heritage. The second major change in the RFS-IIF was to make a significant improvement in the medium to long term stability by using Xenon lamp buffer gas and a thin-film spectral filter in the physics package to reduce shot noise and improve the signal-to-noise ratio (S/N). This has lowered the white FM noise level to below 1x10 -12 tau 1/2 . This paper describes the RFS-IIF design, the changes and improvements made, and the test results obtained. It also discusses the recent redesign activities to eliminate obsolete parts in the RFS-IIF as well as improvements and updates to the PerkinElmer test facility funded by the USAF GPS Wing (GPSW) under the Rubidium Atomic Frequency Standard Modification (RAFSMOD) Program.