Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502384
M. Peca, M. Vacek, V. Michálek
Architecture of a time-to-digit converter (TDC) is presented. TDC is an electronic device which measures time of arrival of discrete electronic pulses, with respect to reference time base. Our work on TDC is motivated by its applications in field of long-range laser distance measurement and time synchronization. Unlike earlier time interpolation methods, we have chosen all-digital approach based on pulse propagation through tapped delay line. We do not expect it could outperform recent invention of time interpolation using narrow-band filter excitation [1], [2]. However, our approach relies on a standard digital circuitry only. With space applications in mind, we are implementing the TDC into a space qualified, radiation-tolerant field-programmable gate array (FPGA). On top of related works [4] and [5] on all-digital TDCs, delay line, we try to gather more complete information about the sampled pulse. It is done by sampling of whole bit vector, corresponding to all of the delay line taps. A calibration method based on random pulse source is discussed, including preliminary results. Impact of physical FPGA cell placement on resulting time measurement granularity is observed. Actually measured jitter distribution is compared to normal distribution function, giving an insight of absolute accuracy limit of our approach within the given FPGA platform.
{"title":"Time-to-Digit Converter Based on radiation-tolerant FPGA","authors":"M. Peca, M. Vacek, V. Michálek","doi":"10.1109/EFTF.2012.6502384","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502384","url":null,"abstract":"Architecture of a time-to-digit converter (TDC) is presented. TDC is an electronic device which measures time of arrival of discrete electronic pulses, with respect to reference time base. Our work on TDC is motivated by its applications in field of long-range laser distance measurement and time synchronization. Unlike earlier time interpolation methods, we have chosen all-digital approach based on pulse propagation through tapped delay line. We do not expect it could outperform recent invention of time interpolation using narrow-band filter excitation [1], [2]. However, our approach relies on a standard digital circuitry only. With space applications in mind, we are implementing the TDC into a space qualified, radiation-tolerant field-programmable gate array (FPGA). On top of related works [4] and [5] on all-digital TDCs, delay line, we try to gather more complete information about the sampled pulse. It is done by sampling of whole bit vector, corresponding to all of the delay line taps. A calibration method based on random pulse source is discussed, including preliminary results. Impact of physical FPGA cell placement on resulting time measurement granularity is observed. Actually measured jitter distribution is compared to normal distribution function, giving an insight of absolute accuracy limit of our approach within the given FPGA platform.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"42 1","pages":"286-289"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88479429","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502340
M. Pellaton, C. Affolderbach, G. Mileti, R. Straessle, D. Briand, N. D. de Rooij
We present a study of our in-house made tetracontane wall-coated 87Rb vapour cells for rubidium atomic clock applications. Evolution of the double-resonance (DR) signal during the so-called ripening process of these cells is measured and interpreted. Intrinsic properties of the coated cells post ripening are presented. Intrinsic linewidths below 70 Hz, and moderate temperature coefficients (1.5 × 10−10 /K) are promising cell properties in view of highly compact and miniature atomic clocks.
{"title":"Wall-coated cells for Rb atomic clocks: Study of the ripening process by double-resonance spectroscopy","authors":"M. Pellaton, C. Affolderbach, G. Mileti, R. Straessle, D. Briand, N. D. de Rooij","doi":"10.1109/EFTF.2012.6502340","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502340","url":null,"abstract":"We present a study of our in-house made tetracontane wall-coated 87Rb vapour cells for rubidium atomic clock applications. Evolution of the double-resonance (DR) signal during the so-called ripening process of these cells is measured and interpreted. Intrinsic properties of the coated cells post ripening are presented. Intrinsic linewidths below 70 Hz, and moderate temperature coefficients (1.5 × 10−10 /K) are promising cell properties in view of highly compact and miniature atomic clocks.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"53 1","pages":"87-90"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83287115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502361
E. Portuondo-Campa, S. Kundermann, S. Lecomte
Increasing the compactness and robustness of laser stabilization systems is a critical need for the development of industrial applications of ultra-narrow linewidth lasers. In this aim, a compact optical setup based on the Pound-Drever-Hall scheme with a high finesse cavity was built with overall dimensions of L × W × H = 45 × 35 × 13 cm3. An external cavity diode laser (PLANEX™, RIO Inc.) as well as a distributed-feedback fiber laser (Koheras Adjustik, NKT photonics) were stabilized using this system. The frequency stability was evaluated using a similar setup as reference. The combined relative stability of the systems reached 7·10−15 at 1s.
{"title":"Compact Hz-level linewidth laser system","authors":"E. Portuondo-Campa, S. Kundermann, S. Lecomte","doi":"10.1109/EFTF.2012.6502361","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502361","url":null,"abstract":"Increasing the compactness and robustness of laser stabilization systems is a critical need for the development of industrial applications of ultra-narrow linewidth lasers. In this aim, a compact optical setup based on the Pound-Drever-Hall scheme with a high finesse cavity was built with overall dimensions of L × W × H = 45 × 35 × 13 cm<sup>3</sup>. An external cavity diode laser (PLANEX<sup>™</sup>, RIO Inc.) as well as a distributed-feedback fiber laser (Koheras Adjustik, NKT photonics) were stabilized using this system. The frequency stability was evaluated using a similar setup as reference. The combined relative stability of the systems reached 7·10<sup>−15</sup> at 1s.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"9 1","pages":"174-177"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83661372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502380
S. Grop, B. Dubois, J. Masson, P. Bourgeois, Y. Kersalé, E. Rubiola, G. Haye, V. Giordano
In this paper we present the direct comparison of two microwave Cryocooled Sapphire Oscillators demonstrating a relative frequency stability better than 2×10−15 at short term and of the order of 1×10−14 over one day integration. We also report the frequency stability evaluation of a microwave signal generated from a planar waveguide external cavity laser (PW-ECL) referenced to a Fabry-Perot cavity through optical-to-microwave frequency division with a commercial Er:fiber optical frequency comb owned by the “laboratoire temps-fréquence” (LTF) of the university of Neuchâtel, Switzerland, and the phase noise measurement of the engineering model of the Pharao clock frequency synthesis owned by the “Centre National d'Etudes Spatiales” (CNES) at Toulouse, France. These lastest results were obtained by moving one of our Cryogenic Sapphire Oscillator (CSO) from the FEMTO-ST Institute to these two metrological sites.
{"title":"Direct comparison of two Cryocooled Sapphire Oscillators presenting relative frequency instability at 10−15","authors":"S. Grop, B. Dubois, J. Masson, P. Bourgeois, Y. Kersalé, E. Rubiola, G. Haye, V. Giordano","doi":"10.1109/EFTF.2012.6502380","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502380","url":null,"abstract":"In this paper we present the direct comparison of two microwave Cryocooled Sapphire Oscillators demonstrating a relative frequency stability better than 2×10−15 at short term and of the order of 1×10−14 over one day integration. We also report the frequency stability evaluation of a microwave signal generated from a planar waveguide external cavity laser (PW-ECL) referenced to a Fabry-Perot cavity through optical-to-microwave frequency division with a commercial Er:fiber optical frequency comb owned by the “laboratoire temps-fréquence” (LTF) of the university of Neuchâtel, Switzerland, and the phase noise measurement of the engineering model of the Pharao clock frequency synthesis owned by the “Centre National d'Etudes Spatiales” (CNES) at Toulouse, France. These lastest results were obtained by moving one of our Cryogenic Sapphire Oscillator (CSO) from the FEMTO-ST Institute to these two metrological sites.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"6 1","pages":"267-270"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88848583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502398
P. Guillemot, P. Laurent, J. Achkar, D. Rovera, E. Samain, P. Exertier, S. Leon
The Time Transfer by Laser Link (T2L2) experiment, developed by both CNES and OCA, performs ground to ground time transfer over intercontinental distances. The principle is derived from laser telemetry technology with dedicated space equipment designed to record arrival time of laser pulses at the satellite. Using laser pulses instead of radio frequency signals, T2L2 permits to realize some links between distant clocks with time stability of a few picoseconds and accuracy better than 100 ps.
{"title":"Improvement of comparisons between T2L2 & RF links","authors":"P. Guillemot, P. Laurent, J. Achkar, D. Rovera, E. Samain, P. Exertier, S. Leon","doi":"10.1109/EFTF.2012.6502398","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502398","url":null,"abstract":"The Time Transfer by Laser Link (T2L2) experiment, developed by both CNES and OCA, performs ground to ground time transfer over intercontinental distances. The principle is derived from laser telemetry technology with dedicated space equipment designed to record arrival time of laser pulses at the satellite. Using laser pulses instead of radio frequency signals, T2L2 permits to realize some links between distant clocks with time stability of a few picoseconds and accuracy better than 100 ps.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"144 1","pages":"345-348"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77931051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502407
H. Gong, Shaojie Ni, Weihua Mou, Xiangwei Zhu, Feixue Wang
The short-term frequency stability estimation of GNSS on-board clocks is very important for clock modeling and prediction. Orbit Determination and Time Synchronization (ODTS) method is commonly used to estimate the clock offset, which needs continuous observation by large monitoring ground network and complicate algorithms. COMPASS is on its early stage of construction and has not globally distributed station network for satellites tracking. In this paper, we have analyzed an estimation method based on a single monitoring station observation. Based on this method, a simple method for COMPASS MEO/IGSO on-board clocks estimation using smoothed broadcast ephemeris is presented, and a method for COMPASS GEO on-board clocks estimation using satellite radio ranging (SRR) is also discussed. At the end of this paper, the preliminary estimation results for COMPASS IGSO and GEO on-board clocks by these two methods are presented.
{"title":"Estimation of COMPASS on-board clock short-term stability","authors":"H. Gong, Shaojie Ni, Weihua Mou, Xiangwei Zhu, Feixue Wang","doi":"10.1109/EFTF.2012.6502407","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502407","url":null,"abstract":"The short-term frequency stability estimation of GNSS on-board clocks is very important for clock modeling and prediction. Orbit Determination and Time Synchronization (ODTS) method is commonly used to estimate the clock offset, which needs continuous observation by large monitoring ground network and complicate algorithms. COMPASS is on its early stage of construction and has not globally distributed station network for satellites tracking. In this paper, we have analyzed an estimation method based on a single monitoring station observation. Based on this method, a simple method for COMPASS MEO/IGSO on-board clocks estimation using smoothed broadcast ephemeris is presented, and a method for COMPASS GEO on-board clocks estimation using satellite radio ranging (SRR) is also discussed. At the end of this paper, the preliminary estimation results for COMPASS IGSO and GEO on-board clocks by these two methods are presented.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"345 1","pages":"383-386"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78078716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502388
X. Liu, E. Kroemer, J. Merolla, R. Boudot
This paper reports the key development steps of a Bi-Frequency Bi-Polarization (BiFBiP) laser system that generates from a single externally-modulated Distributed Feedback (DFB) laser source two phase-coherent optical lines resonant on the Cs D1 line (894.6 nm), frequency-splitted by 9.192 GHz and exhibiting linear crossed polarizations. Two different architectures, based on electro-optic modulators as key components for optical sidebands generation, are presented. Residual frequency stability performances of the DFB laser source are measured to be less than 10−11 for integration times up to 200 s. Phase noise performances of the optically carried microwave signal as well as polarization analysis at the output of the BiFBiP system are reported. Using this laser system, Coherent Population Trapping (CPT) resonances with contrast up to 5.8 % in a mm-scale vapor cell and 22 % in a cm-scale cell are preliminary reported.
{"title":"Towards the detection of high-contrast Cs CPT resonances using a single modulated diode laser","authors":"X. Liu, E. Kroemer, J. Merolla, R. Boudot","doi":"10.1109/EFTF.2012.6502388","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502388","url":null,"abstract":"This paper reports the key development steps of a Bi-Frequency Bi-Polarization (BiFBiP) laser system that generates from a single externally-modulated Distributed Feedback (DFB) laser source two phase-coherent optical lines resonant on the Cs D1 line (894.6 nm), frequency-splitted by 9.192 GHz and exhibiting linear crossed polarizations. Two different architectures, based on electro-optic modulators as key components for optical sidebands generation, are presented. Residual frequency stability performances of the DFB laser source are measured to be less than 10−11 for integration times up to 200 s. Phase noise performances of the optically carried microwave signal as well as polarization analysis at the output of the BiFBiP system are reported. Using this laser system, Coherent Population Trapping (CPT) resonances with contrast up to 5.8 % in a mm-scale vapor cell and 22 % in a cm-scale cell are preliminary reported.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"11 1","pages":"304-308"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74752960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502372
V. Stofanik, Z. Brezović, M. Minárik
In this paper we illustrate our experimental investigations of drive level dependencies of two higher overtones (the 5th and the 7th ones), as well as of the main mode (the 3rd overtone) of several different stress compensated (SC) quartz resonators. The drive level dependencies of basic parameters in the simple Butterworth-Van Dyke one-port equivalent circuit of the particular mode were derived from the impedance vs. frequency responses measured in the vicinity of the particular modes, while temperature of the investigated resonator was maintained approximately at the lower turnover point temperature of the main mode. In the 3rd overtone 10-MHz SC quartz resonators, for example, the 5th overtone or the 7th overtone (the c-modes, i.e. the slow thickness-shear modes of vibration) can be exited simultaneously along with the main c-mode, with assistance of an appropriate dual-mode or multi-mode crystal oscillator (DMXO or MMXO); and the resonator self-temperature-sensing can be reliably implemented [1], [2], [3]. Level of amplitudes of particular modes, which are simultaneously excited in DMXO or MMXO, has impact on short-term, as well as on long-term frequency instabilities of generated signals; hence drive levels of individual c-modes have to be set-up properly in the oscillator circuit.
{"title":"Investigation of drive level dependencies of higher overtones in SC quartz resonators","authors":"V. Stofanik, Z. Brezović, M. Minárik","doi":"10.1109/EFTF.2012.6502372","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502372","url":null,"abstract":"In this paper we illustrate our experimental investigations of drive level dependencies of two higher overtones (the 5th and the 7th ones), as well as of the main mode (the 3rd overtone) of several different stress compensated (SC) quartz resonators. The drive level dependencies of basic parameters in the simple Butterworth-Van Dyke one-port equivalent circuit of the particular mode were derived from the impedance vs. frequency responses measured in the vicinity of the particular modes, while temperature of the investigated resonator was maintained approximately at the lower turnover point temperature of the main mode. In the 3rd overtone 10-MHz SC quartz resonators, for example, the 5th overtone or the 7th overtone (the c-modes, i.e. the slow thickness-shear modes of vibration) can be exited simultaneously along with the main c-mode, with assistance of an appropriate dual-mode or multi-mode crystal oscillator (DMXO or MMXO); and the resonator self-temperature-sensing can be reliably implemented [1], [2], [3]. Level of amplitudes of particular modes, which are simultaneously excited in DMXO or MMXO, has impact on short-term, as well as on long-term frequency instabilities of generated signals; hence drive levels of individual c-modes have to be set-up properly in the oscillator circuit.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"20 1","pages":"227-234"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80884512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502406
M. Siccardi, M. Abgrall, G. Rovera
When speaking of time measurement often no distinction is made between time and time interval but the difference in accuracy between this two cases can be huge. In this paper we will address some of the aspect related to the accuracy in time-tagging a single or repetitive event.
{"title":"About time measurements","authors":"M. Siccardi, M. Abgrall, G. Rovera","doi":"10.1109/EFTF.2012.6502406","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502406","url":null,"abstract":"When speaking of time measurement often no distinction is made between time and time interval but the difference in accuracy between this two cases can be huge. In this paper we will address some of the aspect related to the accuracy in time-tagging a single or repetitive event.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"1 1","pages":"379-382"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83084114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502410
D. Calonico, C. Clivati, G. Costanzo, A. Godone, F. Levi, Marco Marchetti, A. Mura, M. Prevedelli, M. Schioppo, G. Tino, M. Zucco, N. Poli
The Italian Institute of Metrology (INRIM), the European Laboratory for NonLinear Spectroscopy (LENS), the Physics and Astronomy Department of the University of Firenze (UNIFI) and the Politecnico of Torino started a project to establish a 650 km optical fiber link that will enable remote frequency comparisons between high accuracy microwave and optical clocks of INRIM and UNIFI-LENS and an absolute measurement of the UNIFI-LENS Sr clock versus INRIM Cesium fountains. We report the overall architecture of the project, the present status of the experiment and the preliminary tests performed on the equipments.
{"title":"Optical frequency link between Torino and Firenze for remote comparison between Yb and Sr optical clocks","authors":"D. Calonico, C. Clivati, G. Costanzo, A. Godone, F. Levi, Marco Marchetti, A. Mura, M. Prevedelli, M. Schioppo, G. Tino, M. Zucco, N. Poli","doi":"10.1109/EFTF.2012.6502410","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502410","url":null,"abstract":"The Italian Institute of Metrology (INRIM), the European Laboratory for NonLinear Spectroscopy (LENS), the Physics and Astronomy Department of the University of Firenze (UNIFI) and the Politecnico of Torino started a project to establish a 650 km optical fiber link that will enable remote frequency comparisons between high accuracy microwave and optical clocks of INRIM and UNIFI-LENS and an absolute measurement of the UNIFI-LENS Sr clock versus INRIM Cesium fountains. We report the overall architecture of the project, the present status of the experiment and the preliminary tests performed on the equipments.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"37 1","pages":"396-399"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79146799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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