Hybrid clock generator
Clock driver hybrid for hand-held vital signs monitor generates all frequencies required for operation of vital signs system in compact low power configuration.
Rinard, G. A.↗
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Speed of light as measured by two terrestrial stable clocks
Despite the recent criticism within the special theory of relativity, there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously.
Hsu, J. P.↗
Shielding of longitudinal magnetic fields with thin, closely, spaced concentric cylindrical shells with applications to atomic clocks
A general formula is given for the longitudinal shielding effectiveness of N closed concentric cylinders. The use of these equations is demonstrated by application to the design of magnetic shields for hydrogen maser atomic clocks. Examples of design tradeoffs such as size, weight, and material thickness are discussed. Experimental results on three sets of shields fabricated by three manufacturers are presented. Two of the sets were designed employing the techniques described. Agreement between the experimental results and the design calculations is then demonstrated.
Wolf, S. A.↗
Fiber optics transmit clock signal more reliably
Optical automatic gain control smooths maser clock amplitude fluctuations without phase shift. Uncomplicated optical system is more reliable than electrical transmission circuits which require phase-locked loops to compensate for shift. Maser feeds reference signal to linear fiber-optic analog transmitter which emits modulated laser beam directed to splitter. Splitter consists of dichroic mirrors and associated lenses for distributing beam to output ports. Cables attached there guide signals to receiving station.
Lutes, G. F., Jr.↗
Limitations on long-term stability and accuracy in atomic clocks
The limits to accuracy and long term stability in present atomic clocks are examined. Recent proposals for new frequency standards are discussed along with the advantages and disadvantages of frequency standards based on such ideas as laser transitions, single atoms, and atom cooling. The applicability of some of these new techniques to existing standards is examined.
Wineland, D. J.↗
Early results from a prototype VLBI clock monitoring system
Four sets of experiments were conducted to measure the relative epoch offsets between atomic clocks in California, Australia, and Spain by means of very long baseline interferometry (VLBI). The experiments were conducted using an incomplete R & D VLBI system with a number of inherent limitations. The results indicate that the measurement objective of epoch offset to 10 nanoseconds will be met. Tables show the measured offset, the residual to fit, and the square root Allan variance. Graphs show the rate change and the rate reset.
Yunck, T. P.↗
Short turn-around intercontinental clock synchronization using very-long-baseline interferometry
During the past year work was accomplished to bring into regular operation a VLBI system for making intercontinental clock comparisons with a turn around of a few days from the time of data taking. Earlier VLBI systems required several weeks to produce results. The present system, which is not yet complete, incorporates a number of refinements not available in earlier systems, such as dual frequency inosopheric delay cancellation and wider synthesized bandwidths with instrumental phase calibration.
Madrid, G. A.↗
Digital processing clock
Tthe digital processing clock SG 1157/U is described. It is compatible with the PTTI world where it can be driven by an external cesium source. Built-in test equipment shows synchronization with cesium through 1 pulse per second. It is built to be expandable to accommodate future time-keeping needs of the Navy as well as any other time ordered functions. Examples of this expandibility are the inclusion of an unmodulated XR3 time code and the 2137 modulate time code (XR3 with 1 kHz carrier).
Phillips, D. H.↗
Intercontinental clock synchronization with the block 1 VLBI system
The Block 1 very long baseline interferometer (VLBI) operated by the Deep Space Network (DSN) to make weekly measurements of the relative epoch and rate offsets between the time standards in the global network of DSN stations is discussed. The precision of these measurements routinely achieves sub-microsecond levels for epoch offset and accuracies of better than one part in 10 to the 12th power for rate offset. The implementation of the phase calibrator system permits absolute measurement of epoch offset to better than 10 nanoseconds. With the near-real-time play-back and on-line storage of VLBI data, the Block 1 system typically produces clock parameters within 48 hours from the time of observation.
Roth, M. G.↗
The effects of transmitter/receiver clock time-base instability on coherent communication system performance
The purpose of this paper is to present a model and associated analysis of the deleterious effects which both transmitter and receiver data clock time-base instability have on bit-error probability. The types of time-base instability modeled and analyzed include what is commonly referred to as bit jitter (epoch jitter), bit-jitter rate (time interval jitter), and data asymmetry. The bit-error probability is determined as a function of the statistical characteristics of the time-base instability, the data-transition density, the signal-to-noise ratio in the bit-rate bandwidth and the mechanizations of both the data-bit detector and bit synchronizer. The latter is manifested through the bit synchronizer's natural frequency and loop-damping parameters. Numerical results which indicate the sensitivity of the system bit-error rate to various parameters of the model are provided.
Chie, C. M.↗
Estimating Effects of Flicker Noise in Clock Signals
Two techniques mathematically estimate effects of flicker noise in pulse trains used as clock signals.
Wu, S. C.↗
A rubidium clock for SEEK-TALK
The development of a tactical rubidium frequency standard (TRFS) for the SEEK-TALK program is discussed. This effort, which is entering the prototype stage, is directed toward the establishment of a production capability for miniature rubidium clocks of medium stability capable of fast warmup and extreme ruggedness for military avionics applications. The overall unit consists of an ultraminiature physics package and four plug-in circuit boards inside a 2 1/2-inch square by 4-inch box. This size is achieved without the extensive use of hybrid microcircuitry, yet is believed to be the smallest atomic frequency standard yet developed.
Riley, W. J.↗
High-accuracy global time and frequency transfer with a space-borne hydrogen maser clock
A proposed system for high-accuracy global time and frequency transfer using a hydrogen maser clock in a space vehicle is discussed. Direct frequency transfer with a accuracy of 10 to the minus 14th power and time transfer with an estimated accuracy of 1 nsec are provided by a 3-link microwave system. A short pulse laser system is included for subnanosecond time transfer and system calibration. The results of studies including operational aspects, error sources, data flow, system configuration, and implementation requirements for an initial demonstration experiment using the Space Shuttle are discussed.
Decher, R.↗
The effects of transmitter/receiver clock time base instability on coherent communication system performance
The purpose of this paper is to present a model and associated analysis of the deleterious effects which both transmitter and receiver data clock time-base instability have on bit error probability. The types of time-base instability modeled and analyzed include bit jitter (epoch jitter), bit jitter rate (time interval jitter) and data asymmetry. The bit error probability is determined as a function of the statistical characteristics of the time-base instability, the data transition density, the signal-to-noise ratio in the bit rate bandwidth and the mechanizations of both the data bit detector and bit synchronizer. Numerical results are provided.
Chie, C. M.↗
Validation of a fault-tolerant clock synchronization system
A validation method for the synchronization subsystem of a fault tolerant computer system is investigated. The method combines formal design verification with experimental testing. The design proof reduces the correctness of the clock synchronization system to the correctness of a set of axioms which are experimentally validated. Since the reliability requirements are often extreme, requiring the estimation of extremely large quantiles, an asymptotic approach to estimation in the tail of a distribution is employed.
Butler, R. W.↗
On the clock mechanism and the implausibility of the 35 day precessing disk in HZ Herculis/Hercules X-1
The concept of the precessing accretion disk in HZ Her/Her X-1 in its varied forms, to account for the 35 day periodicity in the X-ray flux, has met many objections from a number of workers on various grounds, but it is still being invoked in current publications. These objections are reviewed and additional arguments are presented against the precessing accretion disk model. The implausibility of the disk models is demonstrated. An alternate clock mechanism, based on nonlinear oscillations in the normal star, which provides the modulation of the mass flow is discussed.
Kondo, Y.↗
Testing for a cosmological influence on local physics using atomic and gravitational clocks
The existence of a possible influence of the large-scale structure of the universe on local physics is discussed. A particular realization of such an influence is discussed in terms of the behavior in time of atomic and gravitational clocks. Two natural categories of metric theories embodying a cosmic infuence exist. The first category has geodesic equations of motion in atomic units, while the second category has geodesic equations of motion in gravitational units. Equations of motion for test bodies are derived for both categories of theories in the appropriate parametrized post-Newtonian limit and are applied to the Solar System. Ranging data to the Viking lander on Mars are of sufficient precision to reveal (1) if such a cosmological influence exists at the level of Hubble's constant, and (2) which category of theories is appropriate for a descripton of the phenomenon.
Adams, P. J.↗
International time transfer and portable clock evaluation using GPS timing receivers: Preliminary results
The overall experiment was designed to test the positioning and navigation capabilities of the GPS timing receivers developed by the Naval Research Laboratory (NRL) for the NASA Goddard Laser Tracking Network (GITN). To perform this experiment, a reliable and redundant time scale was set up onboard the ship, and a back-up on shore. This situation provided the opportunity to perform simultaneously a timing experiment ideally divided into two parts, the main objectives of the experimentation being: (1) To test GPS timing receiver synchronization capabilities on a moving platform, and to perform an intercontinental synchronization via GPS between participating international timing laboratories in Europe and in the United States. (2) To evaluate the performance of cesium portable clocks in the field.
Wardrip, S. C.↗