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Frequency transfer (FT) based on Global Navigation Satellite System (GNSS) precise point positioning (PPP) enables global comparison of local time scales that are each connected to a GNSS receiver. We use our in-house PPP software to examine the current limits of this technique and extend the classical analysis approach to new GPS and Galileo signals. We also investigate the impact of receiver clock modeling (RCM). For this, we carried out a dedicated experiment at Germany’s national metrology institute, the Physikalisch-Technische Bundesanstalt (PTB), where four geodetic receivers – operating in a controlled environment – were connected to one single GNSS antenna and the same UTC(PTB) signal. The link instability of two receivers of the same type is better as compared with the use of receivers of different types. Overall, Galileo signals lead to better FT performance than GPS signals. When using the latter, with modern L2C signals we obtain FT instabilities that are at least comparable to those based on legacy L2 P-code observations. The application of RCM especially improves the short-term link instability. Therefore, this should be studied more in-depth in the future since it can be a valuable approach in GNSS-based FT.

By law PTB is entrusted with realization and dissemination of legal time for Germany, which is defined as UTC(PTB) plus one or two hours. During the last 24 months, including December 2019, UTC(PTB) did not deviate from Coordinated Universal Time UTC by more than 3.2 ns. The services of dissemination can be grouped in “traditional”, “IT-based”, and “based on data recording and publishing”. “Traditional”: The standard frequency and legal time transmitter DCF77 is still the most prominent part of PTB’s time services. The number of operational receivers in Germany and Europe is estimated to be more than 100 Million. Monitoring of the equipment operated at the transmitter site has been modernized over the years, and PTB is prepared to offer the service for another decade. Contractual negotiations with the operator of the transmitting facilities are going to start in 2020. The number of accesses to the telephone time service remains at a level above 1500 per day with a slight downward tendency. “IT-based”: PTB’s internet time service installations are distributed in two buildings and have been upgraded. Two devices capable to act as PTP Grandmasters have been installed, one at each location, which receive multiple timing reference inputs, and which are mutually monitored. They feed the three publicly accessible network time protocol (NTP) servers which answer about 6000 requests per second and two NTP servers for internal use. At the same time, the Grandmasters represent two Smart Meter Gateway (SMGW) administrator servers for dedicated customers. Since 2019 PTB provides a test bed for a secure NTP time service based on Network Time Security (NTS). Work is ongoing to exploit the enhanced redundancy and fully activate all monitor and control functions. In response to the perpetual popularity of services in the World Wide Web (WWW), PTB offers a service to distribute legal time via the WWW which has been coded in HTML5. It is accessible from the home page of PTB (www.ptb.de) or directly via https://uhr.ptb.de and offers the feature to display the time difference between the local system clock of the calling device and legal time as received from PTB. Via a commercial fiber-optic time transfer system Deutsche Telekom Technik (DTAG) receives signals of UTC(PTB) at sites in Bremen, Hannover, and, particularly, in Frankfurt am Main where UTC(DTAG) is realized. After a recent calibration, the time comparison between the two UTC realizations via fiber and via the GPS common-view method agree well within the calibration uncertainty. “Based on data recording and publishing”: PTB, like other national metrology institutes (NMI), has published regular reports— the so-called “Time Service Bulletins”—on the offset between GPS time derived from the satellite signals and UTC(PTB) for two decades. Since the last update, similar information on Galileo System Time (GST), including the prediction of the offset between UTC(PTB) and UTC(USNO) (via GPS) and UTC (via Galileo), based on the navigation messages of GPS and Galileo, respectively, is given. These reports shall give confidence that the broadcast GNSS signals provide a good approximation to UTC in both frequency and time. Their observance is usually required by accreditation bodies as part of the process of demonstrating traceability of corresponding measurements in accredited calibration laboratories. “Other activities”: In the framework of EURAMET project TF-1156 “GPS link calibrations in support of CCTF-K001.UTC”, PTB continues to offer calibrations of GPS signal delays in receivers of other European NMIs as well as other research institutes. In recent campaigns the institutes NMISA (South-Africa), IMBH (Bosnia-Herzegovina), and DTAG were visited. Campaigns that are ongoing at the time of writing cover NIMB (Romania), SIQ (Slovenia) and VTT (Finland), the latter employing a newly ensembled receiver kit.

Blindness caused by the eye diseases Retinitis-Pigmentosa and Age-Related-Macular-Degeneration leads to a degeneration of the photoreceptor layer while postsynaptic cells mostly stay intact. In this Paper a new concept for retinal implants is proposed. Instead of converting the incident light to a gray-scale picture with corresponding continuous-value stimulation levels, we here suggest to produce a binary image picture that only highlight edges in order to stimulate the retina solely at points which belong to an edge. An integrated test circuit is designed with a 130 nm BiCMOS process by using cellular neural networks for binary image generation. The circuit yields a simulated maximum rated power consumption of 2.61 mW for a 1000 information processing cells.

A multi-octave receiver chain is presented for the use in a monolithic integrated vector network analyzer. The receiver exhibits a very wide frequency range of 1–32 GHz, where the gain meets the 3 dB-criterion. The differential receiver consists of an ultra-wideband low noise amplifier, an active mixer and an output buffer and exhibits a maximum conversion gain (CG) of 16.6 dB. The main design goal is a very flat CG over five octaves, which eases calibration of the monolithic integrated vector network analyzer. To realize variable gain functionality, without losing much input matching, an extended gain control circuit with additional feedback branch is shown. For the maximum gain level, a matching better than −10 dB is achieved between 1–28 GHz, and up to 30.5 GHz the matching is better than −8.4 dB. For both, the input matching and the gain of the LNA, the influence of the fabrication tolerances are investigated. A second gain control is implemented to improve isolation. The measured isolations between RF-to-LO and LO-to-RF are better than 30 dB and 60 dB, respectively. The LO-to-IF isolation is better than 35 dB. The noise figure of the broadband receiver is between 4.6 and 5.8 dB for 4–32 GHz and the output referred 1-dB-compression-point varies from 0.1 to 4.3 dBm from 2–32 GHz. The receiver draws a current of max. 66 mA at 3.3 V.

A robust and reliable synchronization network, able to distribute signals traceable to a recognized standard, is crucial for the operation of future 5G telecommunication networks. In this article we present the results of time transfer using optical fibers. The main goal is to test the long-term capability of ELSTAB technology (developed by AGH) to deliver time and frequency signals traceable at the sub-nanosecond level to UTC in a real telecommunication environment. In an ongoing cooperation between Deutsche Telekom (DTAG), the Physikalisch- Technische Bundesanstalt (PTB) and AGH University of Science and Technology, we deliver UTC -- as realized by PTB in Braunschweig -- to a test center of DTAG located in Bremen. For this purpose, a fiber optic link has been operated since July 2015. The results obtained show that the operator of a telecom network may use such a stabilized fiber optic link as a reliable source for synchronization signals with a precision and accuracy superior to those obtained using a state-of-the-art GNSS time receiver. Moreover, a fiber optic link delivering UTC traceable signals increases the robustness and reliability of the network's synchronization chain by making it less dependent on GNSS.

On top of positioning, Global Navigation Satellite Systems (GNSS) can be used for time determination and synchronization applications. The European GNSS Galileo is therefore good candidate to offer a dedicated Timing Service, with accuracy, robustness and integrity. In this frame the EGALITE (Galileo Timing Service Extension and Consolidation) project was launched in 2018. The EGALITE project was funded by the EC as part of the Horizon 2020 framework programme and aimed at studying the possibility of developing a EGNSS Timing Service based on Galileo with committed end-to-end performances. The project’s consortium is led by GMV with VVA, Physikalisch-Technische Bundesanstalt and Observatoire Royal de Belgique as partners. The aim of this paper is to provide a summary of the main outcomes of the activities developed in the frame of EGALITE project: • A brief description of the project objectives is provided, including the motivation for developing a EGNSS Timing Service and what is understood by Timing Service. • The integrity capability of the future potential EGNSS Timing Service is addressed including aspects previously mentioned: high-level architecture definition, receiver processing, operational concept, standardisation and certification aspects and Cost Benefit Analysis (CBA) results. • The design of a Legal Time Traceability Service is also proposed in the paper. As will be seen in the paper, we propose EGNSS Timing Services based on Galileo with committed end-to-end performances provided EGNSS Timing Receivers are certified.

The use of disciplined oscillators offers a straight forward tool to establish traceability of the measurands frequency and time to national standards and ultimately to Coordinated Universal Time (UTC). Traceability means that a complete and unbroken chain of calibrations exists from the measurement device to the respective standard, and that each link is characterized by a corresponding uncertainty. We discuss the commonly agreed uncertainty evaluations and place special emphasis on the application of the PTB Time Service Bulletin in this framework. We further briefly discuss aspects regarding accreditation requirements according to DIN EN ISO/IEC 17025 and financial sector regulations according to MiFID II.

Laboratory sources for standard frequency, one pulse-per-second (1pps) ticks, and time-of-day information which receive external time signals to control their built-in oscillators are widely used wherever accurate and stable frequency and time optionally with universal synchronization are required. Nowadays, such devices mostly apply the signals received from the Global Positioning System (GPS), but also signals from alternative Global Navigation Satellite Systems (GNSS), e.g. the European Galileo, or from low frequency transmitters, e.g. WWVB in the U.S. or the German DCF77, are used. The first parts of our paper deal with traceability of measurements of frequency and time pulses to Coordinated Universal Time (UTC) and particularly to UTC(PTB), its realization by the Physikalisch-Technische Bundesanstalt (PTB), using a disciplined oscillator (DO) with standard frequency and 1pps outputs. For this purpose, the role of PTB’s weekly published Time Service Bulletin (TSB) is discussed in detail. The metrological steps for establishing and maintaining traceability are described and uncertainty contributions for both aspects, frequency and time pulses, are discussed. In the last part we discuss how to possibly meet financial sector regulations according to the European MiFID II. We present a procedure as a component for the assessment to provide accurate time through telecommunication networks using e.g. the Network Time Protocol (NTP). Our procedure checks outputs of an NTP server to validate that its 1pps output signal, which is considered as the device’s time reference point, is in accordance with specific requirements and that the provided time-of-day via NTP corresponds to local legal time (modulo integer hours).

The comparison of distant clocks has always been an important part of time metrology. It is important in science in general as well as in everyday applications. Signals from the satellites of the Global Positioning System (GPS) started to be used for the purpose in the early 1980s. This is of course ongoing, and the Time and Frequency Department of Physikalisch-Technische Bundeanstalt (PTB) provides GPS observation data in format RINEX (2.1 and 3.01) and CGGTTS V2E from several receivers on its public ftp-server and to the Bureau International des Poids et Mesures (BIPM). The “golden” reference receiver is still a legacy Ashtech Z12T with the designation PTBB (for RINEX) and PT02 (for CGGTTS) data. PTB also provides GLONASS observation data since a couple of years. Some were used for time comparisons between institutes collaborating with BIPM in the realization of International Atomic Time TAI. At the time of writing, however, no GLONASS data are used for establishing any link in the TAI computation. GLONASS link results are still reported on the BIPM ftp site, e. g. for comparing UTC(PTB) and UTC(SU). In these days, preparations are underway to routinely use signals from the other GNSS that have come to existence. Recently, Galileo and BeiDou have reached a status of early operation phase. In this contribution we thus report on the initial use of Galileo and BeiDou signals in PTB.

A 65nm CMOS power amplifier for frequency-modulated continuous-wave radar (FMCW) applications is presented in this paper. The PA stages are designed to enhance the power-added-efficiency given by the use case scenario of constant envelope in FMCW applications. Therefore, the output stage and the driving stage is implemented as differential pair with a transformer-based matching circuit, since low voltage devices are used, which limit the maximum output power. The output transformer has been designed for high power transfer and reaching an efficiency of 81%. The output stage has a gain of about 6dB and reaching a PAE of 45% at an output power of 13dBm.

A status report is given on current practice and trends in time and frequency metrology. Emphasis is laid on such fields of activity that are of interest in the context of relativistic geodesy. In consequence, several topics of a priori general relevance will not be dealt with. Clocks and the means of comparing their reading are equally important in practically all applications and thus dealt with in this contribution. The performance of commercial atomic clocks did not change significantly during the last 20 years. Progress is noted in the direction of miniaturization, leading to the wide-spread use of chip-scale atomic clocks. On the other hand, research institutes invested considerably into the perfection of their instrumentation. Cold-atom caesium fountain clocks realize the SI-second with a relative uncertainty of close to \(1\times 10^{-16}\), and with a relative frequency instability of the same magnitude after averaging over a few days only. Optical frequency standards are getting closer to being useful in practice: outstanding accuracy combined with improved technological readiness can be noted. So one necessary ingredient for relativistic geodesy has become available. Satellite-based time and frequency comparison is here still somewhat behind: Time transfer with ns-accuracy and frequency transfer with \(1\times 10^{-15}\) per day relative instability have become routine. Better performance requires new signal structures and processing schemes, some appear on the horizon.

Optical time transfer between PTB and Deutsche Telekom started in 2015. Since December 2016 it has been upgraded to a permanent installation connecting PTB and Deutsche Telekom facilities in Hannover and Bremen. In this paper we report on the evaluation of the performance of this installation and describe future perspectives.

GNSS time transfer is a primary method for remote atomic clock comparisons. There are four global satellite navigation systems in operation, named GPS, GLONASS, Galileo and BeiDou. To guarantee the precision, the accuracy and the robustness of Coordinated Universal Time (UTC) generation, multi-techniques strategy has been encouraged by Consultative Committee for Time and Frequency (CCTF) since 2009 for the purpose. In order to realize BeiDou Common-View time comparisons, three GNSS receivers, which can observe BeiDou satellites were installed in the National Time Service Center, Chinese Academy of Sciences (NTSC), and Physikalisch-Technische Bundesanstalt (PTB) has updated two receivers for BeiDou tracking in August 2017. PTB currently is the pivot laboratory in UTC time links. NTSC has about 40 clocks gaining a weight of more than 5-6% of the total UTC clock weight in past years. BeiDou time (BDT) is traceable to UTC through UTC(NTSC). Therefore, it has been a particular motivation to implement time comparisons by BeiDou for the connection between PTB and NTSC. The PTB-NTSC links was established by BeiDou satellites starting in August of 2017 and its time comparison result are within expectations. In order to verify the performance of a BeiDou global service, we also made some preliminary BeiDou time transfer tests between five IGS stations and NTSC.

The comparison of distant clocks has always been an important part of time metrology. It is important in science in general as well as in everyday applications. Signals from the satellites of the Global Positioning System (GPS) started to be used for the purpose in the early 1980s. The methods of signal processing have improved to an extent that time transfer with ns-accuracy and frequency transfer with 10 − 15 relative instability have become routine. The usage of signals from other Global Navigation Satellite Systems gets more and more common and examples of the improvements related to that will be given. Two-Way Satellite Time and Frequency Transfer (TWSTFT) is another method relying on the exchange of signals in the microwave range. Time transfer accuracy at the 1-ns level was demonstrated, and recently new signal structures and processing schemes showed the way for further improvements.

A wideband variable gain amplifier in a 130 nm BiCMOS technology has been designed, manufactured and characterized. The VGA is built of two cascaded differential emitter follower stages, followed by a cascode stage implemented by a common emitter stage and a common base stage. The combination of emitter follower stages with the cascode stage allows a considerably wider frequency response from DC to 110 GHz. It has been shown that a high-pass response can be achieved using emitter follower stages. The high-pass response is cascaded with the low-pass response of the cascode stage to realize a flat broadband output characteristic. This design method requires significantly less chip area than conventional used distributed amplifier for this bandwidth. The area needed for this VGA is 0.024 mm2. The amplifier consumes a current of 80 mA at a supply voltage of 3.3 V.

For monolithically integrated vector network analyzers (VNA) a broadband multi-octave receiver is shown, which exhibit a very wide frequency range from 1–32 GHz. It consists out of a low noise amplifier (LNA) and an active mixer, followed by an output buffer. With the presented design, a maximum achievable conversion gain (CG) of 16.6 dBm can be reached. The main design-goal is a very flat deviation of the conversion gain over five octaves, which eases calibration of the VNA. To realize variable gain functionality, without losing much input matching, special attention is spent to the design and topology of a new extended gain-control circuit (VGC) is shown. A second VGC is implemented in the output buffer, to improve isolation for deactivated channels of the VNA. All bandwidth extension techniques will be explained in detail and flesh out by simulations. Furthermore, a matching lower than −10 dB is achieved between 1 GHz and 28 GHz. The noise figure NFdsb of the broadband receiver is between 4.6 and 5.8 dB for 4–32 GHz and the output-referred 1-dB-compression-point of 0.1–4.3 dBm from 2–32 GHz. The current consumption at a supply voltage of 3.3 V has a value of 66 mA.

We report on the initial use of Galileo signals in the Time and Frequency Department of Physikalisch-Technische Bundeanstalt (PTB). To this end PTB operated five GNSS receivers capable of receiving Galileo Open Service signals with calibrated signal delays for the two frequencies E1 and E5a.

GNSS timing is currently used worldwide in critical real-time systems that require precise synchronization or time-stamping at geographically dispersed sites, such as wireless telecom stations, electrical power grids, and financial services. For applications where multiple equipment needs to be deployed, it is desirable to use low-cost, single-frequency receivers. Increasing demands in cost-saving and accuracy will make the availability of precise single-frequency solutions more and more interesting. In the space operations domain, an application example of GNSS-based synchronization is passive ranging for geostationary satellites. This paper analyzes the application of low-cost GNSS receivers to multi-site synchronization for geostationary satellite orbit determination based of Time Difference of Arrival (TDOA) measurements. The receiver timing signals are measured at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. By comparing the receiver output timepulse with the reference UTC(PTB) timescale clock using a Time Interval Counter (TIC), one can fully characterize the behavior of the GNSS-derived time solution, and also calibrate the average receiver chain delay. It is expected that the largest contribution to the GNSS timepulse error will be the ionosphere.

We report on a new means for obtaining time information via long-wave signals, provided by Europaische Funkrundsteuerung GmbH (EFR) via three transmitters located at Mainflingen, Germany (129.1 KHz), Burg, Germany (139.0 kHz), and Lakihegy, Hungary (135.6 kHz), respectively. The signals are received and continuously monitored by Physikalisch-Technische Bundesanstalt, PTB, in Braunschweig.

We report on the upgrade of a fiber optic network for time and frequency transfer between PTB in Braunschweig and the test center of Deutsche Telekom in Bremen, Germany. The network provides 10 MHz and 1 PPS signals at remote locations intended for the supervision of the mobile telecommunication network of Deutsche Telekom. Here we present the results of the time transfer calibration of the link.

The recent activities in the field of time and frequency dissemination and applications at PTB resulted in improved quality and a wider reach of the offered services. The basis of these activities remains PTB’s local realization of Coordinated Universal Time UTC(PTB). PTB’s time services comprise the operation of NTP time servers, a telephone time service and the standard frequency and time dissemination by the low frequency transmitter DCF77. The number of requests of the public NTP service approaches 7000 per second. The number of accesses to the telephone service remains steady at about 1800 per day. The standard frequency and time signal transmitter DCF77 is still the most prominent of PTB’s time services. The number of operational receivers in Germany and Europe is estimated to be more than 100 Million. In summer 2016 a calibrated GNSS receiver was installed at the transmitter site. Time comparisons between the caesium clock which serves as the reference for the transmitted signal and UTC(PTB) have since then been made with an uncertainty of 5 ns via GPS and Galileo common view. Time and frequency comparisons with institutes all over the world represent an important part of the activities. PTB continues to be the pivot in all GPS and GLONASS comparisons by which the metrology and research institutes world-wide contribute to the realization of UTC. Data from four different GNSS receivers are regularly provided to BIPM. PTB’s “golden receiver”, a legacy Ashtech ZXII-T (acronym PT02), has been found stable and reliable in the very long term, but shows annual delay variations with a peak-to-peak amplitude of about 1 ns, likely related to the outdoor temperature affecting the antenna cable delay. A possible new reference receiver was identified and is going to be tested before eventually taking over the status of PT02. PTB has accepted the role of a so-called “Group1” laboratory that should offer (in cooperation with BIPM and together with French and Spanish institutes) calibrations of GPS time links to other European NMIs and other research institutes. A so-called G1G2 campaign was finished in August 2016, during which relative receiver internal delays of in total 11 receivers belonging to the institutes DLR, METAS, VSL, and BEV were determined with reference to the PT02 delays determined by BIPM in 2014. Draft results of the 2016 BIPM campaign showed that PT02 delay changes amount to not more than 0.5 ns. A similar exercise using travelling GPS receivers was organized by SYRTE/Observatoire de Paris in the frame of the Galileo Time and Geodetic Validation Facility (TGVF) project managed by GMV, Spain, providing similar results. A TWSTFT calibration campaign was once more undertaken by the U.S. Naval Observatory and revealed the excellent long-term stability of the link between USNO and PTB via TWSTFT. The difference between successive calibration values is at the 1 ns level.

We report on the evaluation of the performance of optical time transfer links connecting a facility of Deutsche Telekom in Bremen with the Physikalisch-Technische Bundesanstalt in Braunschweig. In the current configuration three links have been established, two via a hub in Hannover and one using an independent alternate route. They are equipped with electronically stabilized fiber optic time and frequency transfer systems and parallel operation is maintained since December 2016. A novel method of link calibration, composed of two steps (one performed in the laboratory and the second one in the field), to accurately determine the influence of fiber chromatic dispersion is discussed in detail, and a thorough analysis of the uncertainty budget is given. We show that the time transfer performance achieved is difficult to characterize based on measurements with time interval counters that are the standard equipment in timing laboratories and in the telecommunications sector. In our experiments, values of TDEV at the low ps-level at averaging times between 104 to 106 s have been achieved. The uncertainty of time transfer (including all kinds of delays) is of the order of 50 ps in a cascade of links. The results obtained show that such a kind of link is capable to deliver signals to a remote end with an instability being at least two orders of magnitude below the current requirements included in relevant Recommendations of the International Telecommunication Union—Telecommunication Sector (ITU-T). Moreover, the current implementation would allow primary Cs fountain clocks to be compared at the level of their performance, that is characterized by an uncertainty at the low 10−16 level and a frequency instability of the same order of magnitude at 1 d averaging.

The operation of a mobile telecom network relies directly on the synchronization of thousands of base stations that must be robust and operate reliably 24 hours a day. Nowadays networks using advanced Long Time Evolution (LTE) standard need not only frequency syntonization, but also time synchronization that should ideally be traceable to UTC. In this work we present first results of providing UTC(PTB) (1 PPS and 10 MHz) by optical fiber to a test center of Deutsche Telekom in Bremen. The work aimed at a proof-of-concept in real telecommunication environment and the demonstration of the long-term operation capability and scalability of the approach. A potential future application is the comparison of UTC(PTB) and UTC(DTAG).

Oxygen shows significant absorption lines in the millimeter wave spectrum. Resonators are widely used to achieve a strong absorption even with a short absorption paths length for concentration measurements. A sensor system based on a Fabry-Perot resonator for oxygen measurements at ambient pressure is presented here. The Fabry-Perot resonator consists of two metal mirrors with a diameter of 50 mm. For purpose of oxygen detection the resonator covers a frequency range between 55 GHz and 65 GHz with a resonant peak density between 1 GHz and 1.5 GHz, depending on the mirror distance, and a quality factor of approximately 7000. To achieve a compact sensor system the concept envisages two integrated transceiver circuits directly coupling to coaxial ports in the metal mirrors of the resonator. The integrated SiGe front-end addresses a frequency band from 50 GHz to 75 GHz. They are realized as heterodyne structures with integrated directional couplers, thus it is possible to measure scattering parameters. For first oxygen concentration measurements, the resonator sample was coupled to a commercially available Vector Network Analyzer. The cavity was filled with oxygen concentrations of 0% vol. and 20% vol. at ambient pressure and temperature resulting in a significant change of the quality factor for frequencies close to the oxygen absorption line at 60.6 GHz. The sensor does not contain hot components. This is an advantage compared to other oxygen sensors, like electrochemical or metal-oxide sensors.

Global satellite navigation systems (GNSS) are a standard measurement device for deformation monitoring. In many applications, double-differences are used to reduce distance dependent systematic effects, as well as to eliminate the receiver and satellites clock errors. However, due to the navigation principle of one way ranging used in GPS, the geometry of the subsequent adjustment is weakened. As a result, the height component is generally determined three times less precisely than the horizontal coordinates. In addition, large correlations between the height and elevation dependent effects exist such as tropospheric refraction, mismodelled phase center variations, or multipath which restricts the attainable accuracy. However, for a kinematic analysis, i. e. for estimating high rate coordinate time series, the situation can be significantly improved if a common clock is connected to different GNSS receivers in a network or on a baseline. Consequently, between-station single-differences are sufficient to solve for the baseline coordinates. The positioning geometry is significantly improved which is reflected by a reduction of the standard deviation of kinematic heights by about a factor 3 underlining the benefits of this new approach. Real data from baselines at the Physikalisch-Technische Bundesanstalt campus at Braunschweig where receivers are connected over 290 m via an optical fiber link to a common clock was analysed. © 2016 Walter de Gruyter GmbH, Berlin/Munich/Boston.

The Physikalisch-Technische Bundesanstalt (PTB) has substantially improved the quality of its local time scale UTC(PTB), which is the national realization of the international time reference Coordinated Universal Time (UTC). It serves as the basis for PTB's time services, for local clock comparisons and for international time comparisons. Since February 2010 UTC(PTB) has been realized using an active hydrogen maser (AHM) steered in frequency via a phase micro-stepper according to an algorithm which combines the frequency comparison data between the AHM and primary and commercial caesium clocks of PTB. Thereby the long-term stability and accuracy of PTB's primary clocks, in particular its fountain clock CSF1, were combined with the short-term frequency stability of the AHM. CSF1 data were used to calculate the steering on all but six days during 15 months. During the time between July 2010 and July 2011, the time difference between UTC(PTB) and UTC was always less than 6?ns and the monthly mean rate differences never exceeded 0.16?ns per day.

Two-way satellite time and frequency transfer (TWSTFT) has become an important technical component in the process of the realization of International Atomic Time. To employ the full potential of the technique, especially for true time transfer, a dedicated calibration is necessary. This consists of the calibration either of the operational link at large, including every component involved, or of the involved ground stations' internal delays only. Both modes were successfully employed by circulating and operating a portable reference station between the sites involved. In this paper, we summarize the theoretical background for the different calibration modes applied and report examples of results from the 13 calibration campaigns performed up to now in Europe and between Europe and the United States. In all of these exercises, estimated uncertainties around 1?ns were achieved. Consecutive campaigns showed a very good reproducibility at the nanosecond level. Additionally, we address and briefly discuss sources that possibly limit the uncertainty for true time transfer employing TWSTFT.

This paper presents a planar multilayer six-port circuit implementation based on multi-octave directional couplers. The presented six-port circuit is the first published six-port, that is capable of operating in an ultra-boradband frequency range from 2 to 30 GHz. Within this spectrum the six-port allows for the determination of the complex reflexion coefficient through four scalar power measurements. The six-port circuit is based on the quasi-optimal design proposed by Engen. Proper functionality has been verified through measurements of the S-parameters and the calculated q-points.

International audience; In the Galileo FOC phase (Full Operational Capability), GMV is the prime contractor for the Time and Geodetic Validation Facility (TGVF), a contract of the European Space Agency (ESA). Within the TGVF, the Time Validation Facility (TVF) is the subsystem in charge of steering Galileo System Time (GST) to UTC, among other duties. The new TVF is operated at GMV headquarters in Madrid, Spain. TVF operations rely on the contribution of five European timing laboratories, located at INRiM, OP, PTB, ROA, and SP. This paper provides a general description of the TVF element and its related activities for the FOC phase, and presents the main results and findings of the TVF operation until now.

International audience; Since 2010 ROA has supported the coordination of the EURAMET Technical Committee for Time and Frequency (TC-TF) Project 1156, a response from EURAMET TC-TF to Recommendation 2 of CCTF 2009: to study the characterization of GNSS equipment in use for establishing the time links between institutes contributing with their clocks to TAI. Starting that year, a GPS calibration campaign was organized between three contributing laboratories: ROA (Spain), PTB (Germany) and INRIM (Italy). The time transfer results were achieved by using the P3 method, and also carrier phase PPP comparison techniques. These results were also used to re-calibrate the TWSTFT (Two-Way Satellite Time and Frequency Transfer, TW for short) links between labs, with an uncertainty slightly higher than that of the GPS links.During 2011 and 2012, the campaign was repeated, and in 2012 two other laboratories were included in the calibration trip: NPL (United Kingdom) and OP (France). In this paper we report the calibration results, with a focus on the long term stabilities of the GPS and TW links between the visited labs.

This paper deals with the local realization of Coordinated Universal Time UTC by PTB, named UTC(PTB), and PTB's free atomic time scale TA(PTB). Since February 2010 UTC(PTB) has been derived from an active hydrogen maser steered in frequency by PTB's primary fountain clocks. Since then and up to early 2015 the time difference UTC - UTC(PTB) was always less than 9 ns. From early on it was foreseen that the steering of UTC(PTB) could also be derived from the ensemble of caesium beam clocks operated in PTB. When doing so in practice, it appeared that the algorithm of combining the inputs of individual clocks was not perfectly chosen. The properties of the time scales as generated up to now as well as the new strategy for a time scale reflecting better PTB's ensemble of thermal beam caesium clocks is presented in this paper.

GMV is the prime contractor for the Time and Geodetic Validation Facility (TGVF) in the Galileo FOC phase (Full Operational Capability), a contract of the European Space Agency (ESA). Within the TGVF, the Time Validation Facility (TVF) is the subsystem in charge of steering Galileo System Time (GST) to UTC, among other duties. The TVF is operated at GMV headquarters near Madrid, Spain. Calibrated Galileo receivers are needed in the frame of TVF activities to, among other tasks, assess the UTC-GST offset broadcast in the Galileo navigation message. Absolute receiver calibration is a complex activity involving the availability of a signal simulator and of a calibrated reference antenna. An alternative data-based method to evaluate the Galileo receiver delay in E5 signals relative to GPS is also possible. The key feature of such method is the cancellation of the GPS and Galileo ionospheric delays when combining pseudoranges from two satellites with a close position in the sky. A software tool called gecal has been developed by GMV within the Galileo TVF, implementing such method and processing RINEX 3 observation files. Satellite positions are read from a SP3 orbit file. The tool allows the rapid E5 calibration of a new or existing Galileo receiver. This paper describes the tool and the calibration of three Galileo receivers used in the TVF. Galileo Signal-In-Space validation results obtained using such receivers are also presented.

International audience; We report about a GPS receiver relative calibration campaign, which took place between five European National Metrology Institutes or Designated Institutes: LNE- SYRTE in Observatoire de Paris (Paris, France), where the reference receiver of the campaign was located, ROA (San Fernando, Spain), SP (Borås, Sweden), PTB (Braunschweig, Germany) and INRIM (Torino, Italy). We used as traveling equipment two main units, both connected to a single antenna, and we kept track of the offset between both traveling units in all the visited sites. An external validation of the resulting hardware delays is provided against the time scale differences derived from the UTC UTC(k) data published by BIPM in its monthly Circular T. Thanks to a very good stability of the traveling equipment, we obtained expanded uncertainty estimates within 2.0 ns (k = 2) for the hardware delays.

Based on the current state of technology, distance measurements over a few hundred metres in air with relative uncertainties significantly better than 10_6 are still an almost impossible challenge. In the European Joint Research Project (JRP) “Metrology for long distance surveying” measurement uncertainties in GNSS-based and optical distance metrology are going to be thoroughly investigated, novel technologies and primary standards developed and guidelines to improve surveying practice in the field worked out. A better understanding and a decrease of measurement uncertainty is also targeted for the critical local tie measurement at geodetic fundamental stations.

International audience; Istituto Elettrotecnico Nazionale Galileo Ferraris (IEN), National Institute of Standards and Technology (NIST), National Physical Laboratory (NPL), Laboratoire National de Métrologie et d'Essais---Observatoire de Paris/Systèmes de Référence Temps Espace (OP) and Physikalisch-Technische Bundesanstalt (PTB) operate cold-atom based primary frequency standards which are capable of realizing the SI second with a relative uncertainty of 1 × 10-15 or even below. These institutes performed an intense comparison campaign of selected frequency references maintained in their laboratories during about 25 days in October/November 2004. Active hydrogen maser reference standards served as frequency references for the institutes' fountain frequency standards. Three techniques of frequency (and time) comparisons were employed. Two-way satellite time and frequency transfer (TWSTFT) was performed in an intensified measurement schedule of 12 equally spaced measurements per day. The data of dual-frequency geodetic Global Positioning System (GPS) receivers were processed to yield an ionosphere-free linear combination of the code observations from both GPS frequencies, typically referred to as GPS TAI P3 analysis. Last but not least, the same GPS raw data were separately processed, allowing GPS carrier-phase (GPS CP) based frequency comparisons to be made. These showed the lowest relative frequency instability at short averaging times of all the methods. The instability was at the level of 1 part in 1015 at one-day averaging time using TWSTFT and GPS CP. The GPS TAI P3 analysis is capable of giving a similar quality of data after averaging over two days or longer. All techniques provided the same mean frequency difference between the standards involved within the 1sigma measurement uncertainty of a few parts in 1016. The frequency differences between the three fountains of IEN (IEN-CsF1), NPL (NPL-CsF1) and OP (OP-FO2) were evaluated. Differences lower than the 1sigma measurement uncertainty were observed between NPL and OP, whereas the IEN fountain deviated by about 2sigma from the other two fountains.