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Frequency References

 

Every day Symmetricom’s scientists define the state of the art of highly accurate, highly stable time and frequency measurement. As authorities in the global timing community, they lead the way in developing new timing standards and products. Symmetricom’s frequency references, in particular, include some of the world’s most advanced timing technology in terms of precision, stability, low-power consumption, portability, ruggedness, and design innovation. Learn about these concepts from the experts who invented them.

MHM 2010™ Active Hydrogen Maser In Depth

The world’s most widely installed active hydrogen maser employs the ideal timekeeping technologies for applications that require extreme frequency stability, low phase noise and long service life.

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A Modern Militarized Rubidium Frequency Standard

This white paper describes the design of the Symmetricom Model 8130A Rubidium Frequency Standard (RFS), modern ruggedized RFS intended for military applications and other harsh environments.

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Dynamic Two-Way Time Transfer to Moving Platforms

Time based communications (TBC) involves the use of an active data channel for time transfer. In 2002, testing was conducted with the Air Force Research Lab (AFRL) at Wright Patterson Air Force Base to demonstrate a TBC implementation from the ground to an airborne platform using standard communications channels and equipment. Algorithms to perform Dynamic Two-Way Time Transfer (DTWTT) have been developed to correct raw time transfer data for platform motion and measurement effects. The flight experiment is presented with a description of the data collection hardware as well as a detailed presentation of the flight data. Conclusions on the use of DTWTT are drawn based on the results of the flight tests.

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Optically-Pumped Cesium Beam Frequency Standard for GPS-III (PTTI Conference 2001)

We describe an optically-pumped cesium beam frequency standard under development for deployment on the GPS-III satellite constellation. In particular, we discuss the design choices that have been made with particular emphasis on optical pumping and interrogation techniques, laser and optical technologies, and the realization of the prototype frequency standard. Preliminary performance data is presented.

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Platforms Using Commercial Satellite Modems

Time based communications (TBC) involves the use of an active data channel for time transfer. Algorithms to perform Dynamic Two-Way Time Transfer (DTWTT) have been developed to correct raw time transfer data for platform motion and measurement effects. This paper begins with a review of Time Based Communications followed by the introduction of DTWTT. A flight experiment is presented with a description of the data collection hardware as well as a detailed presentation of the flight data. Conclusions on the use of DTWTT are drawn based on the results of the flight tests.

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The Long-Term Stability of the U.S. Naval Observatory's Masers (PTTI Conference 2004)

The authors are developing a chip-scale atomic clock (CSAC), more than two orders of magnitude smaller and lower power than any existing technology. As an intermediate milestone, en route to the ultimate CSAC objectives, we have developed a Miniature Atomic Clock (MAC), combining the low-power CSAC physics package with a low-parts count, low power digital control and microwave system. The MAC provides a valuable testbed for the further development and refinement of the CSAC physics package as well as for the development of the CSAC control electronics.

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Rubidium 8040C

This white paper highlights how Symmetricom has helped communication device manufacturers meet their challenges for several years as the market-leader in rubidium frequency standard devices. Read about how the 8040C offers higher levels of accuracy, redundancy and flexibility for manufacturers and laboratory testing-companies that need precise frequency verification.

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Rubidium Keeps the Signal Stable

This white paper describes the advantages of using a Rubidium Atomic frequency standard to provide a stable reference (clock) for a digital exciter. It highlights how a rubidium oscillator is not only more economical and requires less maintenance than other solutions.

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Stochastic Model Estimation of Network Time Variance

This white paper presents a study of clock drift in computers and other networked devices. The paper starts with an introduction to clock architecture, distribution of standard time, drift in oscillators, and efforts to improve clock precision. This is followed by an equation for clock drift that shows the how the calculation for modeling drift in networks was established. Finally, statistical projections are presented along with results and conclusions about the significance of network clock error, even in relatively small networks.

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Symmetricom’s MHM 2010™ Active Hydrogen Maser… In Depth

This white paper provides an overview of some of the many Active Hydrogen MASERs, delivered by the Symmetricom Sigma Tau Standards Group over the past 20 years. Read about the MHM 2010, the first commercially available Active Hydrogen Maser in the world with stand-alone Cavity Auto Tuning and how this technique, developed by the Symmetricom Sigma Tau Standards Group, enables the MHM 2010 to deliver long-term stability normally only attributed to the most stable of cesium atomic standards

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Synchronization Measurement and Analysis

Information on the measurement of phase and analysis as well as examples.

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The MAC: A Miniature Atomic Clock (PTTI Conference 2005)

The authors are developing a chip-scale atomic clock (CSAC), more than two orders of magnitude smaller and lower power than any existing technology. As an intermediate milestone, en route to the ultimate CSAC objectives, we have developed a Miniature Atomic Clock (MAC), combining the low-power CSAC physics package with a low-parts count, low power digital control and microwave system. The MAC provides a valuable testbed for the further development and refinement of the CSAC physics package as well as for the development of the CSAC control electronics.

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The Miniature Atomic Clock – Pre-Production Results

The authors have developed a Miniature Atomic Clock (MAC) for applications requiring atomic timing accuracy in portable battery-powered applications. Recently, we have completed a pre-production build of 10 devices in order to evaluate unit-to-unit performance variations and to gain statistical confidence in the performance specifications, environmental sensitivity, and manufacturability.

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The Role of Time and Frequency Systems in the Power Industry

This application note discusses how the massive 2003 power outage that left over 50 million people in the dark did indeed shed light on one critical issue facing power companies — the role of synchronized timekeeping.

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VCSELs for Atomic Clocks (SPIE Photonics West 2006)

This paper describes the VCSEL requirements for CPT-based atomic clocks, which include single mode operation, single polarization operation, modulation bandwidth > 4 GHz, low power consumption (for the CSAC), narrow linewidth, and low relative intensity noise (RIN). A significant manufacturing challenge is to reproducibly obtain the required wavelength at the specified VCSEL operating temperature and drive current. Data are presented that show the advantage of operating at the D1 (rather than D2) resonance of the alkali atoms. Measurements of VCSEL linewidth are discussed in particular, since atomic clock performance is especially sensitive to this parameter.

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VCSELs for Atomic Sensors

A new generation of small low-power atomic sensors, including clocks, magnetometers, and gyroscopes, is being developed based on recently available MEMS and VCSEL technologies. These sensors rely on spectroscopic interrogation of alkali atoms, typically rubidium or cesium, contained in small vapor cells. The relevant spectroscopic wavelengths (in vacuum) are 894.6 nm (D1) and 852.3 nm (D2) for cesium, and 795.0 nm (D1) and 780.2 nm (D2) for rubidium. The D1 wavelengths are either preferred or required, depending on the application, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources because of their low power consumption and circular output beam.

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1PPS Disciplining

This document describes how to connect a one pulse per second (1PPS ) source such as a commercial GPS receiver to an X72 to achieve long term accuracy and excellent holdover or flywheeling performance.

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