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  • 1
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    Performance data of US Naval Observatory VLG-11 hydrogen masers since September, 1983 (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: In 1983, two VLC-11 masers were delivered to the U.S. Naval Observatory by the Smithsonian Astrophysical Observatory. Last year the short-term stability of these masers was reported and the effect of this short-term stability on timekeeping performance was examined. Since the date of installation, 13 September 1983, data on the masers' long-term performance have been accumulated. The Allan variance, agma(tau), of the relative frequency between the masers reaches a minimum of about 4 parts in 10 to the 16th power at averaging times 5,000 seconds and rises at longer averaging times due, at least partly, to systematic frequency drift. The systematic frequency drifts, expressed in units of fractional frequency difference per day are discussed.
    Keywords: LASERS AND MASERS
    Type: NASA. Goddard Space Flight Center Proc. of the 16th Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting; p 375-384
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    NASA TECHNICAL REPORTS
  • 2
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    High accuracy OMEGA timekeeping (1982)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Smithsonian Astrophysical Observatory (SAO) operates a worldwide satellite tracking network which uses a combination of OMEGA as a frequency reference, dual timing channels, and portable clock comparisons to maintain accurate epoch time. Propagational charts from the U.S. Coast Guard OMEGA monitor program minimize diurnal and seasonal effects. Daily phase value publications of the U.S. Naval Observatory provide corrections to the field collected timing data to produce an averaged time line comprised of straight line segments called a time history file (station clock minus UTC). Depending upon clock location, reduced time data accuracies of between two and eight microseconds are typical.
    Keywords: LASERS AND MASERS
    Type: NASA. Goddard Space Flight Center Proc. of the 13th Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting; p 187-198
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    NASA TECHNICAL REPORTS
  • 3
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    Atomic hydrogen maser measurements with wall surfaces of carbon tetrafluoride (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The principal objectives of the Smithsonian Astrophysical Observatory cold maser research programs are given. This work is aimed principally at understanding more about the interaction of hydrogen atoms with wall coatings of fluorinated ethylene propylene (Dupont Teflon FEP-120 co-polymer) and of carbon tetrafluoride (CE4). The principal measured quantity in these experiments is the wall shift of the maser's output frequency. The wall shift per atomic collision was calculated from the measured wall frequency shift. This assumes that the wall surface area is smooth on a molecular scale.
    Keywords: LASERS AND MASERS
    Type: NASA. Goddard Space Flight Center Proc. of the 16th Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting; p 351-374
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    NASA TECHNICAL REPORTS
  • 4
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    Design of the stift time and frequency transfer microwave ground terminal (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Satellite Time and Frequency Transfer System is intended to provide, simultaneously, global time comparisons at the subnanosecond level and frequency comparisons to better than 1 part in 10 to the 14th power. It utilizes an orbiting hydrogen maser clock and frequency standard that communicates, via microwave links, time and frequency information to Earth terminals operated by hydrogen masers controlling local clocks. A two-way microwave link, to and from the space vehicle provides Doppler information used to cancel the Doppler shifts in a one-way link from the spaceborne oscillator. Pseudo-random noise (PRN) modulation in the two-way link also provides range information to cancel the range delay in the PRN time transfer between space and Earth. The pseudo-random noise modulation system for time difference measurement and its incorporation in the Doppler cancellation system for frequency comparison is explained. The particular PRN code sequence selected and an analysis of the system is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Goddard Space Flight Center Proc. of the 14th Ann. Precise Time and Time Interval (PTTI) Appl. Planning Meeting; p 223-242
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    NASA TECHNICAL REPORTS
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