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Search Publications by: Judah Levine (Fed)

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Displaying 26 - 50 of 111

International Comparisons of Network Time Protocol Servers

December 4, 2014
Author(s)
Michael A. Lombardi, Judah Levine, Jose M. Lopez, Francisco Jimenez, John Bernard, Marina Gertsvolf, Harold Sanchez, Oscar G. Fallas, Liz C. Hernandez Ferero, Ricardo de Carvalho, Mario Fittipaldi, Raul Solis, Franklin Espejo
This paper describes a recently designed system that measures the time transmitted by network time protocol (NTP) servers located in North, Central, and South America. Direct measurements of the time transmitted by each server are obtained by comparing the

Time Transfer Using a Satellite Navigation System

January 1, 2013
Author(s)
Judah Levine
Article does not have an abstract. It was solicited by the editors of the yearbook and was written based on their detailed comments about the topics to be covered, the technical detail, etc. It is intended for high-school students and contains material

GPS Carrier-Phase Time Transfer Boundary Discontinuity Investigation

November 26, 2012
Author(s)
Jian Yao, Judah Levine
We report on a study of the carrier-phase time transfer boundary discontinuity by the use of the precise point positioning (PPP) technique. Carrier-phase time transfer is first compared with two-way satellite time and frequency transfer (TWSTFT) between

Synchronizing Computer Clocks by the Use of Kalman Filters

November 14, 2011
Author(s)
Judah Levine
The National Institute of Standards and Technology (NIST) currently operates 35 public network time servers that are located at many different sites in the United States. The servers provide time messages over the public Internet in a number of different

Synchronizing Computer Clocks Using Kalman Filters

July 31, 2011
Author(s)
Judah Levine
I have used the Kalman Filter algorithm to improve the link between the Internet Time Servers operated by the National Institute of Standards and Technology (NIST) and the primary atomic clock ensemble in Boulder, which realizes UTC(NIST) and which is used

Timing in Telecommunications Networks

July 20, 2011
Author(s)
Judah Levine
I describe the statistical considerations used to design systems whose clocks are compared using dial-up telephone lines or the Internet to exchange timing informaiton. The comparison is usually used to synchronize the time of a client system to the time

A review of time and frequency transfer methods

December 5, 2008
Author(s)
Judah Levine
I will discuss three methods of transmitting time and frequency information: one-way, two-way and common-view. I will describe the advantages and limitations of the different methods including ncertainty estimates for systems that are based on them.

Improvements to the NIST Network Time Protocol Servers

December 5, 2008
Author(s)
Judah Levine
The National Institute of Standards and Technology operates 22 network time servers at various locations. These servers respond to requests for time in a number of different formats, and provide time stamps that are directly traceable to the NIST atomic

Realizing UTC (NIST) at a Remote Location

December 5, 2008
Author(s)
Judah Levine
I will describe the backup time scale system that I have constructed at the site of the NIST radio stations near Fort Collins, Colorado, and I will compare its performance to the primary ensemble in Boulder. The Fort Collins system is designed to be a

Steering a Time Scale

December 1, 2008
Author(s)
Judah Levine
A time scale is a procedure for combining the data from an ensemble of clocks or frequency standards. The input data to the ensemble algorithm are generally the time (or frequency) differences between each of the members and the reference device for the

A Straightforward Frequency-Estimation Technique for GPS Carrier-Phase Time Transfer

September 15, 2006
Author(s)
C Hackman, Judah Levine, Thomas E. Parker, Dirk Piester, Juergen Becker
GPS carrier-phase time transfer (GPSCPTT) offers high frequency stability at short averaging times, approaching a fractional frequency stability of 10 -15 at an averaging time of 1 d. However, a discontinuity occurs in the time-transfer estimates between

Adding Water Vapor Radiometer Data to GPS Carrier-Phase Time Transfer

December 7, 2004
Author(s)
C Hackman, Judah Levine
When analyzing GPS carrier-phase time transfer (GPSCPTT) data, it is often necessary to estimate the zenith troposphere delay (ZTD) at each site as a function of time. That is because the index of refraction of the troposphere varies rapidly. Both the ZTD

Coping with Overload on the Network Time Protocol Public Servers

December 7, 2004
Author(s)
David Mills, Judah Levine, Richard Schmidt, David Plonka
The public time servers operated by USNO and NIST provide time synchronization, directly or indirectly, to millions of Internet computers today. The load in the form of processor cycles and network traffic has doubled in the last two years and could

A New Technique for Estimating Frequency from GPS Carrier-Phase Time Transfer Data

August 28, 2004
Author(s)
C Hackman, Judah Levine, Tom Parker, Dirk Piester, Juergen Becker
GPS carrier-phase time transfer (GPSCP1T) offers high frequency stability at short averaging times, approaching a fractional frequency stability of 10-15 at averaging times of one day. However, a discontinuity occurs in the time transfer estimates between