There has been an increased focus on precise time and frequency transmission dissemination at a national and international level recently. We would like to present the situation in the Czech Republic, our strategy, approach, and our experience with a non-commercial, cost-effective solution that utilizes shared optical networks. The presented solution provides accurate time and stable frequency at a lower operational cost, utilizing the shared spectrum of the CESNET3 network infrastructure. We are committed to future developments and upgrades that will include the next wavelength bands and geographic extensions. Additionally, we have implemented bidirectional dark channels on various wavebands, which utilize shared leased fibers and offer bidirectional compensation for fiber losses. However, operating precise time and frequency requires a single path with bidirectional amplification performed by optical amplifiers, which are sensitive to feedback from the fiber line induced by back-scattering, and reflections, and which can cause unwanted oscillations. We have addressed this issue by carefully solving the interference with parallel data transmissions. In summary, we have implemented a cost-effective solution for precise time and frequency dissemination in the Czech Republic, which utilizes shared optical networks. We are committed to future developments, and we are also part of a consortium that plans to realize a Pan-European network to offer time and frequency services to a broad range of users.
National Infrastructure for Dissemination of Precise Time and Coherent Ultra-stable Optical Frequency - CITAF
Vojtěch, J., Smotlacha, V., Havlis, O., Šlapák, M., Altmannová, L., Kundrat, J., Bhowmick, S., Vohnout, R., Velc, R., Pospíšil, P., Kuna, A., doc. Ing. Jaroslav Roztočil, CSc.,
Proceedings of the 53rd Annual Precise Time and Time Interval Systems and Applications Meeting. Manassas, VA: The Institute of Navigation (ION), 2022. p. 235-242. ISSN 2333-2085. ISBN 978-0-936406-31-2.
In the article, we introduce the Czech Infrastructure for Time and Frequency activity which is a non-commercial, open activity focused on the transfer of accurate time and very stable frequency using optical networks. The national optical infrastructure for time and frequency transfer is operated on top of the CESNET network infrastructure, to have operational costs under control. We briefly summarize the history of its development, together with the used types of optical transfer and its stabilization. We also address running and planned upgrades and future development plans regarding wavelength bands and considered geographic extensions.
National Infrastructure for Dissemination of Precise time and Interconnection of Quantum sources of ultra-stable optical frequency CITAF
Vojtěch, J., Havlis, O., Šlapák, M., Altmannova, L., Smotlacha, V., Pospíšil, P., Kundrat, J., Vohnout, R., Velc, R., Andriantsarazo, E., doc. Ing. Jaroslav Roztočil, CSc.,
Proc. SPIE 12502, 22nd Polish-Slovak-Czech Optical Conference on Wave and Quantum Aspects of Contemporary Optics. Bellingham (stát Washington): SPIE, 2022. Proc. of SPIE. vol. 12502. ISSN 0277-786X. ISBN 978-1-5106-6111-0.
Precise Time and Frequency dissemination and its essential infrastructure on national or even international level are being focused recently. We present here the situation in Czechia, our strategy and approach to contribute with experience of non-commercial solution, open activity utilizing optical networks shared with other data traffic. The cost efficient solution of accurate time and very stable frequency is realized, and operated within shared spectrum of CESNET network infrastructure; the costs are under control then. We are focused on future developments, plans, upgrades concerning wavelength bands and geographic solutions and extensions. Bidirectional dark channels on various wavebands, we do realize them to utilize shared leased fibres, bidirectional compensation of the fibre losses is the benefit or must for these solutions. When operating precise Time and Frequency, single path with bidirectional amplification performed by optical amplifiers is preferred, however it is sensitive to feedbacks by fibre line, caused mainly by back scattering, reflections, and potential to cause unwanted oscillations. The interference with parallel data transmissions is the issue being carefully solved. Within this paper, we also briefly mention CLONETS Design Study project where we share the experience, and the consortium is about to plan and realize the coherent Pan-European Time and Frequency dissemination network to interconnect national research network, and to provide various Time and Frequency services for a wide range of users, research, non-commercial and commercial as well.
Large scale infrastructure for precise time and frequency bidirectional transmission
The paper presents the possibilities of precise time and frequency transfer and comparison of ultra-stable time scales using the national optical infrastructure CITAF (Czech Infrastructure for Time and Frequency).
Long Haul Single Fiber Reamplified-Reshaped White Rabbit Transmission
2021 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS). Institute of Electrical and Electronics Engineers Inc., 2021. ISSN 2327-1949. ISBN 978-1-6654-3935-0.
The paper presents a comparison of optically amplified single fiber White Rabbit (WR) transmission and single fiber 2R regenerated (Reamplify-Reshape) WR transmission using affordable 2R regenerators, which could ensure precise time transmission over several hundred kilometers of fiber.
Porovnávání časových stupnic UTC(FEL) a UTC(TP) pomocí technologie White Rabbit
Článek popisuje inovovaný systém pro porovnávání stupnice UTC(FEL) generované cesiovými hodinami 5071A/001 v. č. 3519 v Laboratoři přesného času a frekvence FEL ČVUT (Praha 6, Dejvice) a národní časové stupnice UTC(TP) udržované v Laboratoři státního etalonu času a frekvence (Praha 8, Kobylisy). Původní systém využíval pro porovnávání metodu společných pozorování (Common-View) pomocí GNSS přijímačů GTR 51/55 a současně dvoucestnou metodu přenosu času po optických vláknech pomocí optoelektronických adaptérů MATRIX. Nová metoda porovnávání je založena na technologii White Rabbit, která je v časových laboratořích FEL ČVUT, ÚFE AV a CESNET předmětem výzkumu od roku 2019.
Towards Czech national research infrastructure for Clock Network Services
Article summarizes past and continuous development, and especially current state of Czech national research infrastructure for Clock Network Services and future development plans. The focus is on used transmission means and stabilization techniques, available and planned wavelength bands and also plans for geographic extensions.
Alternative spectral window for precise time fiber based transport
Precise time and also stable frequency transfers are approaching the state to become almost standard applications for optical fiber networks, especially they are becoming supported in multiple research and education networks. In principle, the time and frequency transfers are not possible to be implemented over data transport layer, which hasn't been was designed for essential stability, and thus dedicated wave band is required for such implementation. To achieve even better stability for precise time and stable frequency, the bidirectional transmission in single physical medium (fibers and ideally all components along the route) is preferred. The White Rabbit system combines synchronous Ethernet and Precise Time Protocol (IEEE-1588) and it has been designed in the CERN with the aim to provide time synchronization among large number of sensors, actuators and other devices utilized in experiments. Primary aim was the operation over single fiber (to avoid nonreciprocal changes in directions) using standard telecommunication transceivers designed for single fiber operation with reach limited to about 40 km. In this paper, we experimentally verify and compare stability of White Rabbit system operation over long distances up to 300 km using active optical amplification on wavelengths which should not be utilized within spectrum needed for regular data transmissions.
Direct clock optical transmission using commercial SFP transceivers for metropolitan network
This paper presents experimental verification of possibility of affordable direct transmission of frequency over lossy metropolitan fiber and comparison of short to midterm performance with White Rabbit technology, which is broadly accepted as sub 1 ns timing standard by the community.
Infrared dissemination of precise time and frequency over optical fibers in Europe
The paper focuses on showing past, current and ready to start time and frequency (metrology) projects taking place in Europe aimed to long haul time and frequency transfers over optical fibers. It addresses both EURAMET and Horizon2020 projects' scope. Focus will be given to Coordination and Support Action project CLOck NETwork Services (CLONETS) - Strategy and innovation for clock services over optical-fibre networks and proposed subsequent design study CLONETS-DS. Attention will be given also to effort of Research and Education Networks (NRENs) as pioneer network operators into this field.
Systém přenosu času mezi Laboratoří přesného času a frekvence FEL ČVUT a Státním etalonem času a frekvence
Článek seznamuje s řešením systému přenosu času po optických vláknech mezi Laboratoří přesného času a frekvence FEL ČVUT (Praha 6, Dejvice) a Laboratoří státního etalonu času a frekvence (Praha 8, Kobylisy).
Fast Comparison of High-Precision Time Scales Using GNSS Receivers
Comparison of high-performance time scales generated by atomic clocks in laboratories of time and frequency metrology is usually performed by means of the Common View method. Laboratories are equipped with specialized GNSS receivers which measure the difference between a local time scale and a time scale of the selected satellite. Every receiver generates log files in CGGTTS data format to record measured differences. In order to calculate time differences recorded by two receivers, it is necessary to obtain these logs from both receivers and process them. This paper deals with automation and speeding up of these processes.
Presented standard is intended for use in time and frequency calibration laboratories as a source of UTC-synchronized time scale with high longterm stability or for clock synchronization in distributed systems and sensor networks. Similar device was utilized for measurement published in the report Evaluation of timing GPS receivers for industrial applications for the 12th IMEKO TC10Workshop.
Live Demonstration: Time and Frequency Standard Based on GPS Receiver
Presented standard is intended for use in time and frequency calibration laboratories as a source of UTC-synchronized time scale with high longterm stability or for clock synchronization in distributed systems and sensor networks. Similar device was utilized
for measurement published in the report Evaluation of timing GPS receivers for industrial applications for the 12th IMEKO TC10 Workshop.
MEASUREMENT OF TIME BASE CHARACTERISTICS OF HIGH RESOLUTION DIGITIZERS
To increase the quality of synchronization in industrial distributed systems is a frequent demand at present. Node synchronization can be implemented in the Ethernet network using time protocols, e.g. IEEE 1588 Precise Time Protocol (PTP). However, active network components like switches and routers have negative influence on achieved accuracy of synchronization because they affect a packet delay variation in the network. To suppress this effect, special (but expensive) industrial switches, with a packet propagation delay correction, can be used. Another way using either low cost GPS receivers for synchronization of local clocks or a special timing for data transfer is described in the paper. It will allow a cheaper solution that preserves high quality of synchronization. Besides, a device for packet delay measurement (PTP tester) was designed and developed to be possible to evaluate the proposed methods.
Měření parametrů časových základen digitalizátorů spojit ých signálů s vysokým rozlišením
Node synchronization can be implemented in an Ethernet network using time protocols; e.g. IEEE 1588 . Active network components like switches and routers influence the accuracy of synchronization because they affect a packet delay variation in the network. Therefore, the delay is not constant and, as well, the delay in one direction is not equal to the delay in the opposite direction.
This paper presents a low-cost device that can measure the packet delay with high accuracy in both communication directions and, at the same time, calculate network parameters including a packet delay variation, path asymmetry and dependency of the delay in opposite directions.
The measurements can be used for the estimation of synchronization accuracy within the tested network. Some network elements have an unexpectedly large variability of path delays and large asymmetry. This behavior can be measured directly and therefore it is possible to eliminate these devices from the network. The results can be also used for the manual calibration of end nodes. It is not recommended, however, as it is vulnerable to network topology changes.
Node synchronization can be implemented in an Ethernet network using time protocols; e.g. IEEE 1588. Active network components like switches and routers influence a precision of the synchronization because they affect the packet delay in the network. Therefore, the delay is not constant and also the delay in one direction is not equal to the delay in the opposite direction.
This paper presents a low-cost device that can precisely measure the packet delay in both communication directions and, at the same time, calculate network parameters; e.g. the packet delay variation, the path asymmetry and dependency of the delay in opposite directions.
Measured values can be used to determine the usability of the network for the IEEE 1588 implementation and to predict the quality of the synchronization in a network. These measurements are important to achieve a precise synchronization in a low-cost network infrastructure.
Evaluation of timing GPS receivers for industrial applications
Synchronization of measurement and control units (nodes) in large distributed systems is a common problem of
industrial automation. Efficient solution is based on using local time bases controlled (synchronized) by timing
GPS receivers. For their industrial application, sufficient accuracy and stability of generated synchronization
pulses and an acceptable price are required. Modern timing receivers satisfy these requirements.
This paper evaluates two GPS receivers suitable for industrial “online” applications, the uBlox LEA-6T and the
Trimble ICM SMT, both priced under $100 USD.
Advanced Distributed Measuring Systems - Exhibits of Application. 15 ed. Aalborg: River Publishers, 2012. p. 95-120. The River Publishers Series of Information Science and Technology. ISBN 978-87-92329-72-1.
The synchronization of large systems is important for recording of dynamic actions and data acquisition of physical quantities over a wide geographical area. The chapter deals with synchronization of distributed measurement systems, especially synchronization using PTP (Precise Time Protocol, IEEE 1588). A practical case study presents a Master Clock module synchronized by GPS receiver. This module works as a high quality time base for PTP based system.
Device for Time Scale Generation and Event Timestamping
This paper describes the design of a device for precise time scale generation (tied to UTC)
and the identification of time events. During the development great emphasis was placed on the highest possible accuracy while preserving low cost.
Evaluation of Accuracy of Timestamping Using Direct Memory Access Controller
2011 IEEE International Symposium on Precision Clock Synchronization for Measurement, Control and Communication (ISPCS 2011) Proceedings. Technical University of Munich, 2011. pp. 1. ISBN 978-1-61284-892-1.
Timestamps of events are used in distributed measurement systems to enable data correlation. This paper presents a technique of timestamping events in a microcontroller using a direct memory access (DMA) controller. The microcontroller is configured to trigger each separate data word memory transfer. This feature can be used to trigger the transfer using an external event and thus transferring the current timestamp to memory by the direct memory access controller when each event occurs.
Comparison of IEEE 1588 Implementations Using the STM32 Connectivity Line Processor
In distributed system containing multiple clocks, precision time synchronization can by achieved using IEEE 1588 protocol. This paper presents a hardware assisted and a software implementation using the STM32 Connectivity Line (STM32C) processor. Accuracy of time synchronization depends on stability of master and slave oscillators, timestamping technique and reference clock adjustment capabilities. Allan deviation of both master and slave are measured to determine oscillator stability. Several tests using a hardware and software timestamping are made. Synchronization performance is also tested using an internal reference clock and using internal general purpose timers/counters.
Frequency Selection of Sine Wave for Dynamic ADC Test
The paper deals with determination of an optimum frequency for the time domain and frequency domain ADC testing. Proposed algorithm for selection of test signal frequency fulfills two common requirements. The first requirement is to get maximum quantity of distinct phases of the sampled values which are uniformly distributed between 0 and 2π; the second one is to avoid overlapping of higher harmonic components aliased in the first Nyquist zone. The algorithm was verified using MATLAB simulations and practical measurements.
Selecting Sinewave Test Frequencies for Dynamic ADC Tests
The precise selection of the input and sampling frequencies, and selection of the record length are very important for dynamic testing of AD converters and modules by sine wave signal. IEEE Std 1241-2000  and Std 1057-2007  provide standardization in the ADC testing. Selection of optimal input testing signal frequency under these standards is resolved separately for applied deterministic testing methods. To compare results between each test method, it is necessary to use identical test conditions inclusive of identical input
testing signal frequency. That is why an algorithm of input testing signal frequency selection was developed to allow both the sine-fit and the DFT methods to be applied.
Sine Wave Signal Sources for Testing High-Speed High-Resolution A/D Converters
This paper presents an analog-to-digital converter (ADC) embedded as a peripheral in
a microcontroller and influence of asynchronous digital input signals on results of ADC conversion. A schematic diagram of a SAR ADC peripheral analog input circuit in a microcontroller was described and its model was designed. A practical measurement was performed using crosstalk measurement setup and causes of measurement errors were identified.
Zdroje sinusových signálů pro testování rychlých analogově-číslicových převodníků s vysokým rozlišením
Based on a model of a test signal generator, an accuracy estimator was designed and implemented. The proposed estimator uses computer simulations to obtain expected bias of dynamic parameters of an analog-to-digital converter (ADC). The usage of the method for estimation of ADC dynamic parameters measurement accuracy for the best sine-wave fit and the frequency domain analysis using the DFT will be presented in this paper.
Client-Server Based Education Tool for Measurement Applications
The paper presents advanced modular conception of software designed for purpose of dynamic ADC testing at the Department of Measurement, FEE CTU in Prague. Main principles of development, the structure and functionality of software blocks and application modes are discussed.
Influence of Test Signal Phase Noise on High-Resolution ADC Testing
The testing of high-resolution ADCs based on the majority of standardized methods requires pure sine-wave test signal. The reason of the requirement for signal's purity is that measured ADC parameters are potentially influenced by test signal imperfections such as distortion and wideband noise but also its short term frequency changes (phase noise). The influence of signal distortion and noise has already been the subject of many contributions; an analysis of phase noise, its effect on test results and possibilities of its suppression or correction are the subject of this paper. The validity of phase noise analysis and of proposed methods is also demonstrated on experimental measurements.
Osciloskopy, přístroje na pořizování dat - přehled trhu
The paper presents a complete system for remote measurement. The system is based on the client-server communication structure over the Internet. One part considers the client application - it is used by a user to control the measurement. Second part deals with the server - the server application itself and local connection the instruments over the IEEE-488 interface bus. The communication between client and server is built on TCP connection.
The paper deals with methods of a sine-wave signal generation for dynamic testing high-speed (1 MSa/s) to 100 MSa/s) ADCs with high resolution (14 to 20 bits). The techniques of noise and distortion measurement of spectrally-pure sine-wave signals are also discussed.
System for Testing Middle-Resolution Digitizers Using Test Signal up to 20 MHz
In the last years, universal measurement setup for high-resolution ADC testing at the frequency of 1 MHz was designed and prototyped at the Dept. of Measurement, CTU FEE. The experience and good measurement results initiated the extension of the system frequency range up to 20 MHz. In this paper, the extended measurement setup is introduced in two versions: low-cost version enabling the testing of 11-13 bit ADCs and high-quality version for the evaluation of even 20 bit ADCs.
Testing of Middle-resolution Digitisers at Input Signal Frequency of 1 MHz
A system for the testing of digitisers in the frequency range of 1 MHz was developed at the Dept. of Measurement, CTU FEE a few years ago. Two alternates of the system were manufactured - a precision design using special high-quality LC filters with a near-linear transfer characteristic and a low-cost design employing common LC filters using coils with ferromagnetic cores. Both alternates were used for testing several types of middle-resolution digitisers (12-18 bit).
The close-to-carrier noise measurement can be provided by a specially designed notch filter to suppress the dynamic range of sine-wave signal produced by high-quality signal generators. Filter design and experimental measurements at several commercial generators are presented in the paper.
Evaluation of ADC Testing Systems Using ADC Transfer Standard
A transportable high-stable reference AD device was designed and built for a comparison of systems for testing the dynamic quality of ADCs or AD modules. Three different input modules can be used in the frequency range up to 5 MHz. First, this paper refers to the results of an AD device application in the frequency range of the testing signal up to 100 kHz (comparison of four ADC testing systems in different laboratories, evaluation of a short time amplitude and/or frequency instability of testing signal generators). Second, it describes the first experience of its application in the frequency range from 100 kHz to 5 MHz.
Remote Access to the System of Alternative Energy Sources
Proceedings of the 14th International Symposium on New Technologies in Measurement and Instrumentation and 10th Workshop on ADC Modelling and Testing. Gdynia/Jurata: IMEKO TC-4, 2005, pp. 331-334. ISBN 83-89786-37-0.
The paper presents a distributed control and remote monitoring system of alternative energy sources situated in Herbertov. The whole system consists of two main parts. The data acquisition and control part of the system is based on an embedded controller with a hard real-time operating system (PharLap). The remote access and monitoring part uses internet connection via GSM/GPRS network.
Sine-Wave Signal Distortion Measurement at Higher Frequencies
Noise and distortion measurement of sine-wave signal can be provided by a specially designed notch filter to suppress the dynamic range of sine-wave signal produced by high-quality signal generators. Filter design and experimental measurements at several commercial generators are presented in the paper.
System for the Testing of High-resolution ADCs at Frequency of 1 MHz
IMTC05 - Proceedings of the IEEE Instrumentation and Measurement Technology Conference. Ottawa: IEEE Instrumentation & Measurement Society IEEE Ottawa Section, 2005. pp. 278-281. ISBN 0-7803-8880-1.
A system for the testing of ADCs at the frequency range of 1 MHz was designed and prototyped at the Dept. of Measurement, CTU FEE. Two methods were applied to suppress the influence of signal distortion: - Filtering by special high-quality filters with a near-linear transfer characteristic - Filtering by low-cost filters and the application of following numerical correction of residual distortion Low-cost as well as high-quality filters were manufactured. Experimental results showed that the method is directly applicable for the testing of ADCs with the ENOB up to 14 in case of low-cost filters and up to 20 in case of high-quality filters. An extension of the method for the testing of ADCs with hither ENOB can bring an application of the frequency spectrum correction method.
Control and Remote Monitoring of Alternative Energy Sources
The paper presents a distributed control and remote monitoring system of alternative energy sources situated in Herbertov (South Bohemia) - a teaching and research center of the Faculty of Mechanical Engineering, the Czech Technical University in Prague. The data acquisition and control part of the system is based on an embedded controller with a hard real-time operating system (RTOS), the Realtime Embedded ToolSuite (ETS) Kernel.
Harmonic Signal Generation with a High Spectral Purity for High Speed ADC Testing
The paper describes the design and construction of the source of the testing signal with a high spectrl purity for the dynamic testing of the new high speed ADCs with more than 14-bits resolution. The system is based on a common sine-wave signal generator and the precise narrow-band band pass passive filter, and it performs a sine-wave signal with spectral purity higher than 130 dBc. It can be used for the dynamic testing of the ADCs up to 20-bits resolution.
IMTC/03 Proceedings of the 20th IEEE Instrumentation and Measurement Technology Conference. Vail, Colorado: IEEE Instrumentation and Measurement Society, 2003. pp. 1340-1344. ISSN 1091-5281. ISBN 0-7803-7705-2.
A transportable high stable reference AD device was designed and built for a comparison od systems for testing of the dynamic quality of ADCs or AD modules. Three different input modules enable its use in the frequency range up to 5 MHz. First, this paper refers to the results of the AD device application in the frequency range of the testing signal up to 100 kHz (comparison of four ADC testing systems in different laboratories, evaluation of a short time amplitude and/or frequency instability of testing signal generators). Second, it describes the first experience of its application in the frequency range from 100 kHz to 5 MHz.
Evaluation of Short-Time Instability of Generators Used for ADC Testing
The quality of an evaluation of dynamic parameters of ADCs and AD modules is strongly dependent on the quality of testing signal generator. The most important parameters are the signal to noise ratio (SNR) and the spectral purity (THD). Besides, the short-time frequency and amplitude stability are also necessary to be considered, but it is often marginalized. However, they also influence the accuracy of the further evaluation. A possibility, how to estimate this imperfection, is presented in the paper.
Evaluation of Short-Time Instability of Generators Used for ADC Testing
Digital hysteresisgraph can be used for the measurement of dynamic hysteresis loops up to 100 kHz. Digital feedback allows achievement of sinusoidal flux density by iterative modification of the excitation voltage waveform. This approach is used for the measurement of closed (toroidal) samples at higher frequencies.
Short-Term Frequency Stability of Digitizers Testing Signals
KTEM 2000 - Seminář kateder teoretické elektrotechniky a měření elektrotechnických fakult České republiky a Slovenské republiky. Praha: České vysoké učení technické v Praze, 2000. pp. 33-39.
8th Scientific Conference Theoretical Electrical Engineering and Electrical Measurement. Košice: Dep. of Theoretical Electrical Engineering and El. Measurement FEI TU of Košice, 1999. pp. 216-221.
Proceedings of 9th International Symposium on Electrical Instruments in Industry. Glasgow: IMEKO TC-4 Technical Committee on Measurement of Electrical Quantities, 1997, pp. 73-76. ISBN 0-953409-2-X.
Počet efektivních bitů popisuje dynamické vlastnosti zásuvných měř.desek. Systém pro jejich automatické měření se skládá z generátoru sinusového signálu řízeného po sběrnici IEEE 488, PC s testovanou měřicí deskou a řídicího programu
Při aplikaci měřicích desek do PC jsou významné též jejich dynamické vlastnosti. Pro jejich testování byla použita metoda nejlépe proložené sinusovky. Přitom byl zkoumán vliv použitého generátoru a modifikace základní metody
New Measurement and Calibration Methods of Electrical Quantities and Instruments. Budapest: IMEKO TC4 Technical Committee on Measurement of Electrical Quantities, 1996, pp. 88-91. ISBN 963-420-491-0.