Showing papers on "Clock synchronization published in 1972"

Means for synchronizing clocks in a time ordered communications system

Abstract: A time ordered communications system wherein a master station equipped with a master clock which includes a reference oscillator disseminates correct time to remote stations equipped with local clocks which include local oscillators by transmitting a synchronization signal whose time of arrival at the remote station with respect to an internal reference pulse generated by the remote station is a measure of remote station clock error. The time interval between receipt of the synchronization signal and generation of the internal reference pulse is digitally determined to produce an error signal which is used to add or delete local oscillator pulses so as to immediately phase correct the local clock. In addition, the first and second time derivatives of the error signal are obtained and used to compensate the local clock for oscillator drift and other errors.

Integrated collision avoidance, dme, telemetry, and synchronization system

Abstract: A time-sharing cyclic time slot system in which DME range measuring functions, collision avoidance functions, clock synchronization functions and/or data telemetry functions are all combined into an integrated repeating time sharing cycle in a non-interfering manner to achieve either general navigation and traffic control, or else stationkeeping, by the orderly exchange of pulse signals between participating ground stations and/or aircraft, and in which the cost of the system is minimized by using already existing ground and/or airborne VORTAC/TACAN/VOR/DME equipment and tuning the airborne transmitters and receivers in an agile manner to the various frequencies assigned for the performance of the above functions.

Precision and Accuracy of Remote Synchronization via Network Television Broadcasts, Loran-C, and Portable Clocks

Abstract: A comparison among three precise timing centers in the United States has been conducted for more than 1 year using three different synchronization methods The timing centers involved were the United States Naval Observatory (USNO) in Washington, DC, Newark Air Force Station (NAFS) in Newark, Ohio, and the National Bureau of Standards (NBS) in Boulder, Colorado The three methods were cesium beam portable clocks; Loran-C transmissions from Cape Fear, North Carolina, and Dana, Indiana; and ABC, CBS, and NBC network television broadcasts commonly received by the three timing centers Cesium beam portable clocks have the capability of accurately and precisely synchronizing remote clocks to within 01 ?s The Loran-C data involved a 3500 km (2180 miles) ground wave path ? the longest Loran-C ground wave path that has been studied with the precision and accuracy reported herein The long-term precision achieved was about 1 ?s over 1 year The accuracy is limited on occasion by inability to resolve the 10 ?s ambiguity of the 100-kHz pulse train The precision capability of maintaining remote clock synchronization within the majority of the continental United States using network television broadcasts was inferred to be about 5 ns??1/3 s-1/3 over the range of ? from 86 400 s (1 day) to about 107 s (324 days) but with definite accuracy limitations caused by such factors as occasional network re-routing of the television signals Some estimates of the long-term frequency stabilities among the references used at the three timing centers were measured or inferred

Time synchronization via lunar radar

Abstract: The advent of round-trip radar measurements has permitted the determination of the ranges to the nearby planets with greater precision than was previously possible. When the distances to the planets are known with high precision, the propagation delay for electromagnetic waves reflected by the planets may be calculated and used to synchronize remotely located clocks. Details basic to the operation of a lunar radar indicate a capability for clock synchronization to ±20 µs. One of the design goals for this system was to achieve a simple semiautomatic receiver for remotely located tracking stations. The lunar radar system is in operational use for deep space tracking at Jet Propulsion Laboratory and synchronizes five world-wide tracking stations with a master clock at Goldstone, Calif. Computers are programmed to correct the Goldstone transmissions for transit time delay and Doppler shifts so as to be received on time at the tracking stations; this dictates that only one station can be synchronized at a given time period and that the moon must be simultaneously visible to both the transmitter and receiver for a minimum time of 10 min. Both advantages and limitations of the system are given. Finally, an experiment is described which has detected the effects of lunar topography and libration on radar results; a monthly cyclic effect in time synchronization of about ± 6 µs is shown.

Collision avoidance system ground station synchronization

Abstract: A collision avoidance system ground station has its clock phase synchronized with a master clock through the use of a line-of-sight radio link. Multiple two-way synchronization rangings are exchanged between the ground station and the master clock. A digital counter at the ground station obtains the average deviation of the ground station clock with respect to the master clock and applies this average deviation to calibrate or synchronize the ground station clock with the master clock. Subsequently, further multiple two-way synchronization rangings are exchanged between the ground station clock and the master clock. A digital counter at the master clock now obtains the average deviation of the master clock with respect to the ground station clock as a check of the validity of the ground station clock calibration.

An analysis and demonstration of clock synchronization by VLBI

Abstract: A prototype of a semireal-time system for synchronizing the DSN station clocks by radio interferometry was successfully demonstrated. The system utilized an approximate maximum likelihood estimation procedure for processing the data, thereby achieving essentially optimum time synchronization estimates for a given amount of data, or equivalently, minimizing the amount of data required for reliable estimation. Synchronization accuracies as good as 100 nsec rms were achieved between DSS 11 and DSS 12, both at Goldstone, California. The accuracy can be improved by increasing the system bandwidth until the fundamental limitations due to position uncertainties of baseline and source and atmospheric effects are reached. These limitations are under ten nsec for transcontinental baselines.

Clock synchronization circuit

Abstract: The receiver clock of an asynchronous half-duplex data link in a call concentrator is initiated and synchronized by a synchronization circuit which responds to level transitions in a received pulse train and overrides the internal operation of the receiver clock to pull it into synchronism with the transmitter clock each time a level transitions in the receiver clock is out of phase with the corresponding level transitions of the transmitter clock as embodied in the pulse train. The two clocks of the data link are identical and can function either as master or as slave, depending on the direction of transmission.