Standard Time Signals Research Articles

A microprocessor-based generation of standard time and frequency signal format for HF broadcast

Standard time and frequency signals (STFS) for HF broadcasts (e.g. ATA, JJY, WWV etc.) usually consist of an audio tone, a burst of an audio signal every second, a voice announcement at some regular interval of time, etc. The authors describe a generator of such a signal, which is based on microprocessor technology. In this system an audio sinusoidal signal is produced through a digital technique which facilitates the maintenance of the phase relation of the zero crossing of the audio sine wave with respect to that of the second pulse from a standard clock. The burst width is basically controlled by a microprocessor and the basic clock is also run by software. The voice announcement is effected by playing a pre-recorded audio tape. The new scheme, with a dual track-recording system combined with microprocessor controlled management, eliminates the possibility of an incorrect voice announcement caused by tape elongation. The authors describe the functioning of the format generator and discuss its salient features. The generation of the ATA format has been taken as a typical case without loss of generality.

Time Transfer Metrology at NPL, NEW Delhi

The National Physical Laboratory (NPL), New Delhi has the Statutory responsibility to maintain Time Scale UTC (NPL-I) and disseminate standard time and frequency signal (STFS). These aspects are described in this paper.The UTC (NPL-I) is generated via an ensemble of Cesium Clocks. UTC (NPL-I) is intercompared with UTC's of other international time keeping laboratories by continuous monitoring of VLF signal (16 kHz) from GBR (UK) and by receiving time signals from NNSS Satellites which have on-board clocks. Occasional portable clock calibrations have also been carried out. First accurate UTC (NPL-I) calibration was made in May-June 1979 through a two-way time intercomparison between NPL, India and PTB, Federal Republic of Germany via Satellite Symphonie-I.NPL is disseminating standard time and frequency signals at frequencies 5, 10 & 15 MHz under call sign ATA. In the past several experiments on time transfer via satellite Symphonie, APPLE and INTELSAT IV have been performed by NPL with a view to ultimatel...

A Compact Magnetometer Data Acquisition System with Accurate Chronometer

A compact data acquisition system in use for a geomagnetic pulsation study has been constructed. The system is composed of a data processing system controlled by a microprocessor, cassette tape recorder, chronometer and short wave radio receiver. The system is programmed to calibrate the chronometer every five minutes by receiving a standard time signal, such as JJY (Japan), WWV (USA) and so on. The system improves a signal to noise ratio of the radio waves by signal stacking processes to minimize errors in the chronometer calibration. Even in a very weak signal, the system can discriminate a second pulse. The calibration accuracy is 10msec, including circuit signal delay when a radio propagation delay is neglected. The system is programmed to sample three component magnetometer signals at intervals of 3 sec and can store 1.3 Mbytes of data in a C-90 cassette tape which is equivalent to ten-day data. The system is suited for an unmanned operation at a station remote from the standard signal station.

自己浮上式海底地震計用の時刻較正装置

A new clock correction system has been developed for the clock calibration of the ocean bottom seismometer (OBS) before its launching and after its recovery. This system has two standard clocks and one portable time calibrator.One of the standard clocks is synchronized with one of three broadcasted standard time signal waves (2.5, 5.0, 10MHz). Another standard clock uses the oscillation output of a Rb oscillator with a stability about 10-10 per month. The latter can be corrected by the former standard clock when the stability of the Rb oscillator become worse. The portable clock calibrator is synchronized with one of the two standard clocks. This calibrator is able to read the OBS clock and to measure the time difference between the standard clock and the OBS one, and also to send a trigger signal to the OBS clock for the time correction.

Reduction of interstation interference in the transmission of standard frequency and time signals in the high-frequency band

One of the problems encountered by users of standard frequency and time (SFT) signals in the high-frequency (hf) band is the interference between stations transmitting signals in allocated standard frequency bands. This problem has been dealt with in detail by the Seventh Investigation Commission of the International Advisory Con~nittee on Radio Communication. In particular, the IA-I/7 research program foresees an investigation of the possibility of reducing interstation interferency by shifting transmission within the allocated bands and using the most suitable form of modulation. Reduction of interstation interference between signals on the basis of time division (intermittent operation or continuous operation with pulse signals transmitted at different instants of time by each station) are mostly ineffective. In the first case as a result of the considerable time needed for the signals to arrive and in the second case because of the difficulties involved in station recognition.

Improvement of the system for transmitting standard time and frequency signals over radio and TV channels

Methods of measuring time and frequency are widely used in various branches of science and engineering. In particular, these techniques are used in data compression in communication channels, navigation systems, and synchronous broadcasting. In such systems, it is necessary to provide synchronization in time and frequency for spatially separated time scales on the basis of the state standard of time and frequency (SSTF). Research and development work in recent years in the transmission of special time and frequency signals from the standard over various communication channels has gone in hand with the development of automatic receiving and synchronizing devices, which has opened up a new approach to the problem.

Standard frequency and time signals transmitted through all-union televison channels

Standard frequency and time signals transmitted through all-union televison channels

A Pulsar Experiment—Our Experiences in Time Keeping

Our group has been operating over the past five years at Ootacamund, a parabolic mirror array to detect Atmospheric Cerenkov Radiation signals induced by pulsed high-energy (≳200 GeV) gamma ray emission by pulsars. Though the experiment calls for very accurate time-keeping necessitating the use of an atomic clock, we did not have one. We have overcome this difficulty by using a temperature-controlled crystal oscillator with frequent calibrations by signals received by telephone from a nearby atomic clock and by radio from ATA (National Physical Laboratory) broadcast. Relevance of accurate time-keeping to pulsar research is outlined. After a brief description of our experiment, our needs and experiences in time-keeping as well as suggestions for improvement in the broadcast of standard time signals are presented.

Recent Activities on Time and Frequency at the Radio Research Laboratories

The recent activities on time and frequency at the Radio Research Laboratories (RRL), Tokyo are briefly summarized in the following outline:(i) Atomic time scale: Two algorithms for calculating a highly uniform time scale have been developed in order to establish TA(RRL), and the results of the comparison between TA(RRL) and the time scales of foreign organizations are given. (ii) Dissemination of standard frequency and lime signal: A brief description on the measuring and controlling system of the standard frequency and time signal transmissions, JJY (MF and HF) and JG2AS (40 kHz) is given. (iii) T and F satellite experiments: International time-transfer experiment via Navigation Technology Satellite (NTS-1) showed the accuracy of several hundred nanoseconds. Besides, simple correction for ionospheric time delay ruduced the standard deviation by 30% compared with that of the raw data. Experiments of the dissemination of frequency and time were made in 1979 and also in 1980 using the experimental broadcas...

Centralized synchronization of the Moscow TV center: A system for transmitting standard frequency and time signals

Centralized synchronization of the Moscow TV center: A system for transmitting standard frequency and time signals

Coverage Study of ATA Signal Strength in India

In this paper, coverage studies of ATA standard time and frequency transmissions on three carrier frequencies 5,10 and 15 MHz have been reported. The theoretically predicted results agree very well with the SINPO reports received from the AIR stations at some typical locations. This is a first coverage report on ATA transmission. The users of standard time and frequency signals in India will find these studies useful.

Time Synchronization Using Standard Time Broadcast from ATA—NPL

A convenient and accurate method of epoch time synchronization with the help of ATA standard time and frequency signal broadcast is suggested. A clock at a distance of 14 km from the ATA transmitting centre was synchronized by this technique to an accuracy of ±50 μs. The details of this experimental and the data analysis are presented in this paper.

Characterization of phase and frequency instabilities in precision frequency sources: Fifteen years of progress

Precision frequency sources such as quartz oscillators, masers, and passive atomic frequency standards are affected by phase and frequency instabilities including both random and deterministic components. It is of prime importance to have a comprehensive characterization of these instabilities in order to be able to assess the potential utility of each source. For that purpose, many parameters have been proposed especially for dealing with random fluctuations. Some of them have been recommended by the IEEE Subcommittee on Frequency Stability and later by Study Group 7 on Standard Frequencies and Time Signals of the International Radio Consultative Committee (CCIR). Others are not so widely used but show interesting capabilities. This paper aims at giving a broad review of parameters proposed for phase and frequency instability characterization, including both classical widely used concepts and more recent less familiar approaches. Transfer functions that link frequency-domain and time-domain parameters are emphasized because they provide improved understanding of the properties of a given time-domain parameter or facilitate introducing of new parameters. As far as new approaches are concerned, an attempt has been made to demonstrate clearly their respective advantages. To this end, some developments that did not appear in the original references ate presented here, e.g, the modified three sample variance Σ y 2(τ), the expressions of 〈δy- T 2〉, the intetpretation of structure functions of phase and its relations with Σ y 2(τ) and the Hadamard variance. The effects of polynomial phase and frequency drifts on various parameters have also been pointed out in parallel with those of random processes modeled by power-law spectral densities.

The New UTC Time Signals

beginning januaey 1, 1972, the standard time signal broadcasts no longer give directly the rotational position of the Earth to an accuracy of 1/10 of a second of time, as had been done previously. Instead the new UTC Time Signals may depart from the rotational position of the Earth by as much as 9/10 of a second. To retrieve the rotational position of the Earth to an accuracy of 1/10 of a second, it is necessary to apply a supplementary correction DUT1 which is coded into the time signal itself. Methods for using DUT1 in various applications are reviewed.

Precision of Standard Frequency Radio Signals in Relation to Ionospheric and Trans-ionospheric Propagation

The precision of frequency of a standard time broadcast depends on the precision of the frequency standard used to control the transmission as well as on the characteristics of the radio propagation path involved. The advent of atomic clocks, in recent years, have made available frequency standards of such a high precision that the uncertainty in the propagation path now appears to limit the ultimate precision of a standard time signal. The precision can be improved by integration coupled with a suitable choice of the operating frequency. It is the purpose of this paper to review the recent developments in the standard frequency transmission as well as the influence of ionospheric and trans-ionospheric propagation on the frequency of the transmission.

Survey of three megalithic sites in Argyllshire

THREE sites showing simple alignments of standing stones in Argyllshire were tested for possible astronomical significance by members of the Cambridge University Astronomical Society during August and September 1973. The sites were surveyed in detail with a portable (20″ circles) vernier theodolite, on which comprehensive tests were made before and after the expedition to determine adjustment errors; brief checks were made on site. Absolute azimuths were determined accurately by making timed observations of the Sun using MSF Rugby as the standard time signal. The error in azimuth was normally ± 10″ and in altitude ± 20″, although the latter value had to be modified to take account of uncertainties in atmospheric refraction. There is extensive information available on the Ballochroy site1–3, and brief details of the sites at Loch Seil4–6 and Loch Nell4,6 have been published.

Standard Frequency and Time Signal Emission and Its Utilization

Standard Frequency and Time Signal Emission and Its Utilization

The French quadristatic incoherent scatter facility

The original Nançay‐St. Santin incoherent scatter facility based on the radio astronomy antenna at Nançay and a CW transmitter located at St. Santin (300 km south) was improved in many ways between 1965 and 1970: doubling of the transmitted power to 140 kw, lowering of the receiver noise level down to 100 K, monitoring of the antenna and data acquisition through the use of a computer, rejection of the parasitic tropospheric echoes.However, the most important improvement brought to the system is the addition of two new receiving stations 100 km east and west of the transmitter. Each of the new stations is equipped with a three‐beam Cassegrain antenna (25‐m parabola) aimed to simultaneously intersect the vertical transmitted beam at three different heights. Both new receivers have wide band (38 MHz at 3 db) gaseous helium cooled parametric amplifiers and on‐line computers. While one of the two new stations is equipped with filter banks for the purpose of spectral analysis, a different choice has been made for the other station. For the latter the data acquisition will imply multibit correlators, for both the ionic spectrum and plasma line measurements.Most of the improved electronic equipment designed for the new stations has also been implemented in the Nançay receiver. The frequency and time synchronization between the four sites is now accomplished by employing a single 5‐MHz frequency standard in each station monitored by standard time and frequency signals from MSF and/or HBG stations.The observation procedure consists of tilting the different receiving antennas so as to gather the signal scattered from the ionospheric vertical column illuminated by the transmitter. For calibration purposes a standard ionosonde is operating at St. Santin.The main objective of the quadristatic system is to determine completely the ion drift vector in order to study the electric fields and the neutral tidal winds. Other capabilities offered by the new system are a determination of the plasma line and a higher data acquisition rate.The first observations with one of the new stations were performed in December 1972.

A step in time Changes in standard frequency and time signal broadcasts

An improved Coordinated Universal Time (UTC) system has been adopted by the International Radio Consultative Committee (CCIR).* It was implemented internationally by the standard frequency and time broadcast stations on January 1, 1972. The new UTC system eliminates the frequency offset of 300 parts in 1010 between the old UTC and Atomic Time, thus making the broadcast time interval, the UTC second, constant and defined by the resonant frequency of cesium atoms. The new time scale will be kept in synchronism with the rotation of the earth within ±0.7 second by step-time adjustments of exactly 1 second, when needed. A time code will be added to the disseminated time signals that will permit Universal Time to be obtained from the broadcasts to the nearest 0.1 second for users requiring such precision.

Transformation to a new time scale and a new system of transmitting standard frequencies and precise time signals

Transformation to a new time scale and a new system of transmitting standard frequencies and precise time signals