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We describe the operation of the Standard Time & Frequency Signal (STFS) broadcast via INSAT satellite in the so-called online differential mode. The transmission setup at the Delhi Earth station and the recent version ofthe STFS decoder are briefly described. Regular data recording carried out at NPL, New Delhi, NRL, Trombay, field station at Mt Abu and ERTL(E), Calcutta have been used in this paper to draw conclusions regarding improvement in time transfer accuracy.

Magnetite (MAG) and magnetites substituted with nickel, cobalt and chromium (NF, COF and CRF, respectively) have been prepared over the whole range of composition, MexFe3−xO4 (x=0–3, Me=Ni, Co or Cr) using the coprecipitation technique and have been characterized for their chemical composition, crystallinity and surface area. The types of sorption sites present in them were characterized by analysing the water sorption isotherms ultilizing the D'Arcy and Watt equation. Intrinsic dissociation constants, pK ∗ a i and point of zero charge, PZC, were evaluated by analysing the pH-titration curves in acid and alkaline media. A similarity in the trend was observed for the crystallinity, surface area, sorption sites and surface charge characteristics as a function of the composition of the substituted MAGs (i.e. x). The overall behaviour of the substituted MAGs could be grouped into two: mixed oxides having composition with x=0–1 and those in the composition region x=1–3. Those in the composition region x=0–1 were crystalline with a lower surface area, less hydrophilic in nature and have surface charge characteristics lower than that of MAG. Those mixed oxides in the composition region x=1–3 nearly had the opposite characteristics, with increasing value of x. The hydrophilicity of the substituted MAGs decreased in the sequence CRF>NF≫COF, and the acidic nature decreased in the sequence NF>CRF>COF.

We describe the standard time and frequency signal (STFS) broadcast via the INSAT satellite and its use in accurate time synchronization and frequency calibration anywhere in India. Under normal operation it is possible to achieve a synchronization accuracy of better than /spl plusmn/20 /spl mu/s. For users with higher accuracy requirements we discuss the capability of the STFS broadcast to provide time synchronization with an accuracy better than 1 /spl mu/s using a mode of operation which we call differential STFS. Here we further correct the error residuals in the received STFS using data from a reference station collocated with the uplinking site. Both analytical and actual experimental data are presented.

We demonstrate the capability of the Standard Time and Frequency Signal (STFS) broadcast via INSAT to provide time synchronisation with the Indian Standard Time to a 1–2 μsec accuracy in a differential mode. The data used in this study comprise of (a) those recorded at the Giant Metrewave Radio Telescope (GMRT) site at Khodad, Pune and (b) those simultaneously recorded at NPL. GPS receivers have been used at Khodad and at NPL to provide the time reference for measurements of the residual errors of the received STFS time. The residual time error in the received STFS is primarily due to error in the predicted satellite position and is similar at both stations. The common mode error largely cancels in the differential STFS leading to the present high time transfer accuracy.

For small to moderate-sized defects in the head and neck region, local flaps have been the mainstay of reconstruction for years. However, in certain instances, additional flap translation is required be it advancement, transposition or rotation. In such cases, the local flap concept is combined with perforator flap know-how, allowing larger loco-regional flaps to be raised to reconstruct relatively larger defects, even in cosmetically-expensive areas. In our cohort of fifteen patients', we have utilised detailed microanatomy of the facial artery perforators to reconstruct such defects with good results.

Summary In this article, we describe the use of chimeric free fibular flaps to reconstruct three-dimensional spatial defects in the orofacial region. Recent insights into permutations possible with the chimeric fibular flap have allowed us to achieve our reconstructive objectives with a single chimeric flap and minimise donor-site morbidity as well as operating time. In an overall series of 34 free fibular flaps from 2009 to 2012, we performed twelve cases of free chimeric fibular flaps with osseo-myo-cutaneous/OMC ( n = 7), multi-pedicled osseo-musculo-cutaneous/Mp-OMC ( n = 4) and multi-pedicled osseo-cutaneous/Mp-OC ( n = 1) variants for either post-excisional defects or osteo-radionecroses. We had an overall flap survival rate of 100% with one partial flap loss due to the ‘puppeteer' effect. Based on our experiences, we find the chimeric fibular flap to be an excellent addition to our reconstructive arsenal for complex orofacial defects.

The authors discuss the advantages of broadcasting time from a satellite over the more traditional ground based methods such as short wave and low frequency standard time and frequency broadcasts. The authors describe several one way satellite time services currently operational and discuss, in particular, a broadcast service using the Indian domestic satellite INSAT. The signal format, transmitting and receiving setups, and the methods for satellite position prediction are described in detail for the INSAT broadcast. Some typical results of time and frequency calibration are also discussed. >

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.

For the use of satellite-TV signals in a common view mode a detailed analysis relates the prediction errors of satellite co-ordinates to time comparison accuracy. It promises an accuracy better than two microseconds over India with the available quality of satellite ephemerides. The development of an automatic recorder for this purpose improves the measurement capability and its applicability. >

Simultaneous two-way time transfer experiments via satellite symphonie, in which National Physical Laboratory, New Delhi (NPL), Space Applications Centre (SAC), Ahmedabad and Madras Earth Station, Madras (MES) participated, are reported in this paper. The uncertainties involved in alternate one-way mode of clock synchronization reported earlier were removed and a much improved precision and accuracy was achieved. In addition, the results obtained in a Round Robin method, where one station transmits and the other two receive between NPL, SAC and MES are also presented.

Precise time transfers were made and the two atomic caesium clocks at Delhi Earth Station (DES) and Ahmedabad Earth Station (AES) were synchronized to submicrosecond precision, using direct television broadcast of Delhi Doordarshan from DES to AES by the satellite symphonie. A passive technique, where a line-10 of the odd field of TV format was identified and using as the transfer pulse or time marker between participating stations, was used. The limitations and future prospects of this technique, in view of Indian Space Programme, are discussed.

The National Physical Laboratory, New Delhi, as custodian of ‘National Standards of Physical Measurements’, has the statutory responsibility for the establishment, maintenance and dissemination of ‘Time Standard’ in the country. An overview of time and frequency activities at NPL. New Delhi during the last decade is presented.

The UTC (NPLI)* is based on a Hewlett-Packard Commercial Cesium clock out of a group of four such standards. Linkage of this time scale was started in 1979 using VLF signal reception, periodically confirmed using portable clock trips. VLF measurements were continued till middle of 1984. In the meanwhile since 1983, the UTC linkage was supplemented using measurement on the NNSS signal. Using these measurements and similar data obtained from USNO it was possible to obtain a link UTC (NPLI)-UTC (USNO). The results were in good agreement with the VLF measurements except for a discripancy of 15 μsec. The NNSS was discountinued in June 1985 as the USNO data was no longer available.In August 1986, a GPS receiver was acquired and after art initial process of testing and commissioning, regular data taking on an observation schedule prescribed by BIH was started in February, 1987. Using the data in commonview mode with PTB, computations are being made of UTC (NPLI)-UTC (PTB). The GPS data is also currently being co...

The availability of Indian Experimental Satellite “APPLE” gave an opportunity to try out various techniques and to firm up the specifications of the hardware and software required to be developed for precise time transfer, especially in relevance to a time dissemination service via Indian Operational Satellite INSAT-1. Some of the time transfer techniques were earlier experimented with French-German Satellite “Symphonie”. Time dissemination techniques such as TV, both passive and active and transmission of time code likely to be used with satellite INSAT-1B were tried out on APPLE on an experimental basis. The techniques of transmitting one pulse per second (1 PPS) to the satellite was used to range the satellite and it was compared with the conventional tone range technique. A simple, satellite orbit determination programme using the range data was developed and tested. This paper gives the results of the experiments carried out via “APPLE”.

The present paper describes in detail the experimental set-up being used for monitoring of VLF signals at the time and frequency section of NPL, New Delhi. A morphological description is given of the phase and amplitude observation of 16 kHz, GBR for a one-year period since July, 1979. Preliminary results of monitoring the OMEGA signals are also discussed.

The use of TV signals for time comparison is a very well-known technique. The TV signal can be utilized both passively and actively for the same purpose. Recently, this technique has become popular with the use of geosynchronous satellites for TV transmission. Indian Satellite INSAT-1B transmits TV signals to have a full coverage over the Indian subcontinent. So, attempts are being made to utilize these TV signals for time transfer from the National Physical Laboratory (NPL), New Delhi, to other users in India. In the terrestrial TV network, differential propagation delay remains to be a constant factor unless there is a change in the network configuration. But in the satellite TV network, differential propagation delay does not remain constant because the satellite position with respect to the earth does change around its mean value due to the non-circular satellite orbit and nonzero inclination of the plane of the satellite orbit with respect to equatorial plane. So the maximum variations of differential propagation delay about its mean value have been worked out for different locations in India based on some theoretical calculations coupled with findings of some general behavior of INSAT-1B. These observations predict that the variation of differential propagation delay from its mean value will be within 10 μs for most parts of India and half of India will remain even within the range of 5 μs. These observations tally well with those obtained with the help of the actual predictions of satellite positions. Experimental data also corroborate these findings.

The Indian subcontinent does not fall in the groundwave range of any LOKAN-C transmission. As such, at present the only alternative technique in this region for convenient and routinc T & F intercomparison is via VLF phase measurements. At NPL, New Delhi, continuous phase recording of the 16-kHz transmissions from GBR (IK) is being made. In addition, the published mid-day phase data of GBR from several laboratories-NPL (UK). RGO (Uk), PTB (FRG) and USNO (USA)—are being received regularly. In the present paper, we discuss T & F intercomparisons between the local time scale, LTC (India), at NPL and those at the above-mentioned laboratories, using the VLF phase data. A major factor which limits the accuracy of long-term comparison is the seasonal variation in the YLF propagation delay over long paths. It is shown that by taking into account the seasonal propagation delay variations in a semi-empirical way, the accuracy of T & F comparisons can be considerably improved. In fact over a one-year period, accurac...

For the inclusion of date in the digital clock, it is necessary to have counter whose division number should change according to month number of the year as the total number of days is different in...

A recent clock synchronization experiment between the National Physical Laboratory (NPL), New Delhi and Space Applications Centre (SAC), Ahmedabad via geostationary satellite symphonie-II, stationed at 49°E longitude, is reported in this paper. As only one satellite transponder was available for this experiment, the two-way transmission of the clock pulses was carried out by switching the transmit—receive roles at the two stations at 5 minute intervals to achieve a nearly simultaneous two-way transmission. Taking into account all the additional delays, the results demonstrated a clock—synchronisation accuracy of better than 0.5 μs. A crystal-based portable clock flown aboard an aircraft confirmed this clock-synchronization to within a microsecond.

This paper describes the instrumentation, method of monitoring HF time signals (including ATA, New Delhi), determination of the precision of epoch in UTC, signal jitter and signal strength as received at the Satellite Tracking and Ranging Station (STARS, Kavalur) at 5 MHz, 10 MHz and 15 MHz frequencies for the year 1980. The precision of ATA epoch, as determined at the station by comparing it with another International station (RID, USSR), is evaluated for the year 1980.Results obtained at the National Physical Laboratory (NPL, New Delhi) and the Institute of Radio Physics and Electronics (IRE, Calcutta) are compared for an overall assessment of ATA reception in India.

The National Physical Laboratory, New Delhi has developed a portable clock which can be autosynchronised with respect to an external clock pulse to a sub-microsecond level. This clock, which can be easily carried on a plane, train or road transport as a personal baggage, can operate for eight hours on a support power pack without the need of 220 V mains power. This paper describes the technical details of this portable clock and quotes the results of different time transfer experiments carried out with it. The precision achieved in these measurements is of the sub-microsecond order. Further utilisation and development of this portable clock are also discussed.

The present paper describes the design of a Digital Phase Lock Loop (DPLL) for tracking the phase of an input signal of 5 kHz. The DPLL uses 5 MHz external reference frequency sources which is divided down to 5 kHz for phase comparison with the input signal. The phase error depending on the polarity is converted into add or subtract correction pulses which are applied to the reference 2 MHz pulses train. The corrections thus applied, shift the phase of the reference 5 kHz in discrete steps of 0.2 μs in proper direction till phase lock is achieved.The DPLL circuit has been tested both on a simulated signal as well as using received 5 kHz time signals from INSAT. It has been found that an input signal in excess of 200 mV is required for proper locking and the locking range is ±1 parts in 106.

Following the proposal by Bureau International de L' Heure (BIH), Paris the European Space Agency (ESA) has implemented an experimental space mission on-board SIRIO-2 geosynchronous satellite, a payload package, known as LASSO (Laser Synchronization from Stationary Orbit). The LASSO consists of body-mounted array of corner cube retro-reflectors, laser detectors, event timer, precise time standard, TTL-type memory unit and the communication link between satellite and the ground control. The LASSO/SIRIO-2 experiment is designed to employ laser technique for Intercontinental comparisons of clocks at the sub-nanosecond level and for disseminating reference time (UTC) to the user community on a global basis. The satellite is proposed to be launched by ESA in early 1982. Initially, it is planned to position the satellite at a longitude around 25°W, subsequently the satellite will be moved to 20:E. The latter position of SIRIO-2 (20°Ei is the one which will be used in Indian experiments.As the principle, method,...

In this paper, we report a T and F intercomparison experiment between the National Physical Laboratory (NPL), New Delhi, India and Physikalisch-Technische Bundesanstalt (PTB), Federal Republic of Germany, carried out from May 16 to June 29, 1979. The participating earth stations were New Delhi, India and Raisting, FRG. The NPL clock was placed at New Delhi Earth Station and the Raisting Clock was calibrated with PTB/Primary standard via LORAN-C and travelling clocks. The random uncertainty of time comparisons, represented by two sample Allan Variance σ(30 seconds), was less than 10 nanoseconds. The relative frequency difference between the NPL and Raisting Clocks, SNPL, RAIS, as measured over the 44 days period was found to be-15.7 × 10-13. The relative frequency difference between PTB Primary Standard and Raisting Clock, SPTB, RAIS during this period, was measured to be–22.8 × 10-13. The relative frequency difference between NPL clock and PTB Primary Standard, SNPL, PTB, thus, is—7.1 × 10-13.The clock ra...

Several triglycine complexes of rare earth chlorides have been prepared which have composition RCl32H3N+CH2COO−. 3H2O, where R = Y, La, Ce. Pr, Nd, Sm and Dy. The i.r. spectra of these complexes have been interpreted in terms of zwitterion structure of glycine which is coordinated to rare earth cations through oxygens of carboxylic group. The i.r. data together with thermal behaviour of above complexes indicate that water molecules are also coordinated to rare earth ions.

Time and frequency systems are finding their increased use in every branch of science and engineering, day by day. The fields of medicine and biology are, however, still lagging and this needs immediate attention.In this paper, the development of various time and frequency systems is discussed for their possible applications in the field of medicine. A few applications like telemetry of physiological parameters of blood pressure, blood flow, respiration rate and body temperature at suitable frequencies are given. Telemetry of Intensive Care Unit (ICU) and Coronary Care Unit (CCU) data is also cited for emergency treatments.The development of different types of transducers and sensors which are responsible mainly for implantable uses, is given.The proposal for international co-ordination and frequency allocation for biotelemetry of physiological data is discussed in detail. The need for allotment of carrier frequencies for medical applications is emphasized.

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.

The National Phyical Laboratory (NPL), in collaboration with Overseas Communications Service (OCS), has been giving HF time broadcast tinder the call sign ATA since 1959. These signals are being used by a large number of scientific users in India and the neighbouring countries as a reliable source of standard time. Since its inception, the transmitting system of ATA has undergone various stages of development leading to its present state. This paper reviews these stages of development and describes the present set-up in details. The individual responsibilities of NPL and OCS for ATA broadcast are explained. Some future plans for development have also been discussed.Recently, a questionnaire on the usage of ATA was circulated in India. The varied response of the users to this have also been described.

An attempt has been made to compute the received field strengths of ATA transmissions over the Indian Subcontinent. This short communication describes some illustrative results of these computations. These results are expected to serve as useful guide to the ATA users.

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.

The utilization of TV network for precise time-transfer is very well-known. TV telecast in India is usually in the evening hours which limits the extensive utilization of the technique, mainly because of the manning problem. National Physical Laboratory, has developed an automatic recording system to facilitate the data taking. This system automatically switches on the TV receiver at the pre-programmed time, takes the measurements, stores data in the memory cell and switches off the TV after the measurements are over. This will encourage the use of time transfer via TV network in India.