Table of Content

25 June 2020, Volume 40 Issue 3

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Design and Implementation of Changhe No.2 Timing Monitoring Receiver

PAN Feng, LI Guo-jun, YANG Da-feng

2020, 40(3):  1-5.  doi:10.12060/j.issn.1000-7202.2020.03.01

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The long wave timing system is a large ground-based radio timing service system with high timing accuracy in the world at present.Its timing signal adopts the transmission system of loran C signal,which has the advantages of long distance,good stability,high reliability and strong anti-interference ability.For GNSS signals in certain areas vulnerable to interference,volatile lock,designs and realizes a kind of changhe No.2 timing monitoring receiver,the signal integrity test,the ASF(additional quadratic phase factor)delay correction technology,and realized the high precision,high reliability and long time monitoring,can be used as an important supplement to the GNSS timing means.

Prospects for Development of LORAN-C Navigation System for Building up National Comprehensive PNT System

ZHANG Hong-yuan, XU Bing, LI Hai-bo, LIAO Ding-yi, CHEN Hong-qing

2020, 40(3):  6-11.  doi:10.12060/j.issn.1000-7202.2020.03.02

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It has been shown that the progress of building up national comprehensive positioning,navigation and timing(PNT)system at home and abroad,and that developing the Eloran(enhanced Loran-C navigation system)technique with its application abroad.It has been introduced this paper the course of modernization with eLORAN technique for Loran-C navigation system,and discussed that the way for obtaining the information of transmitted time correction,integrity of eLORAN signal,the groundwave additional second factor(ASF)correction along with different propagation path and so on,and for transmitting these information to user terminations,by building the distributed area monitor & difference stations for eLORAN signals.These works is very useful for improving PNT precision and service quality of Loran-C navigation system.It has been pointed furthermore that it is very important to develop user terminations with miniaturization,modularity,intelligence and chip-based,for expanding the application of Loran-C navigation system and for building up national comprehensive PNT system in China.

Progress in Commercialization of Compact Magnetically Selected Cesium Atomic Clocks

CHEN Jiang, MA Pei, WANG Ji, GUO Lei, MA Yin-guang, CUI Jing-zhong, YANG Wei, TU Jian-hui, LIU Zhi-dong, CHENG Da-peng, ZHU Hong-wei, ZHENG Ning, HUANG Liang-yu, YANG Jun, GAO Wei, DONG Peng-ling

2020, 40(3):  12-16.  doi:10.12060/j.issn.1000-7202.2020.03.03

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This paper introduces the progress of the commercialization of the compact magnetically selected cesium atomic clock.The contents include performance,reliability and lifetime of cesium clocks,which have attracted widespread attentions.It is pointed out that the reason why the performance is guaranteed is that the single-beam optics is used in cesium beam tube,and the digital technology in circuit.Some failures and solutions in the early stage of commercialization are given,as well as the environmental adaptability test to further improve the reliability.The paper also discusses the evaluation method of lifetime of the electron multiplier,and puts forward the lifetime evaluation formula which is applicable to some cesium clocks.Finally,some works that need to be further explored in the process of commercialization are pointed out.The methods introduced in this article is not only helpful for the commercialization of magnetically selected cesium atomic clocks,but also has reference value for optically pump cesium clocks and even other types of atomic clocks.

Research Progress of the Active Optical Frequency Standard

SHI Tian-tian, PAN Duo, MIAO Jian-xiang, CHEN Jing-biao

2020, 40(3):  17-21.  doi:10.12060/j.issn.1000-7202.2020.03.04

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The frequency stability of clock-transition laser in traditional passive optical clocks is ultimately limited by the Brownian noise,which is one of the main technical bottlenecks restricting the development of optical frequency standards.The active optical clock,utilizing the weak feedback of optical cavity to form coherent stimulated radiation between atomic-transition levels,is a novel laser.The atomic stimulated emission of active optical clock can be used as the clock-transition laser directly,therefore,compared with the passive part,the active optical clock can achieve narrower quantum limited linewidth and has the advantage of suppressed cavity-pulling effect.This paper reports the development of active optical frequency standards at home and abroad,and focus on its theoretical and experimental progress in Peking University.We proposed the dual-wavelength good-bad-cavity scheme to reduce the influence of the residual cavity-pulling effect on the Cesium(Cs)four-level active optical clock.The Nd:YAG 1 064 nm and Cs 1 470 nm lasers share one cavity and works in good- and bad-cavity regime,respectively.The good-cavity laser is frequency stabilized by the Pound-Drever-Hall(PDH)technique to stabilize the cavity length.Then the linewidth of the bad-cavity laser is expected to be further narrowed compared with the stabilized good-cavity laser,considering that the suppression of cavity-pulling effect in bad-cavity regime.Currently,the beating linewidth of 1 470 nm lasers is limited by the asynchronous change of cavity lengths of two dual-wavelength systems.In order to suppress the effect of common-mode noise of cavity-length on 1 470 nm beat-note signal,and verify the feasibility of PDH technique for cavity-length stabilization in dual-wavelength scheme,we put forward the phase locking technology to synchronize the cavity-length variation between two dual-wavelength systems.The influence of other factors besides residual cavity-pulling effect on 1 470 nm active optical frequency standard is further analyzed.

Towards a Miniaturized CPT Atomic Clock based on Constructive Polarization Modulation

LI Qing-lin, Peter YUN, YU Shao-shao, LI Xiao-dong, ZHANG Shu-hong, JU Bo-wen, WANG Xin, HAO Qiang, GAO Yu-ping, ZHANG Shou-gang

2020, 40(3):  22-26.  doi:10.12060/j.issn.1000-7202.2020.03.05

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The passive vapor cell atomic clock based on the coherent population trapping(CPT)has become a competitive candidate for high performance atomic clocks for its excellent short-term stability(2E-13@1s)and medium-term stability(2.5E-15@10⁴s).A high-performance miniaturized CPT atomic clock based on a new configuration is studied here.We compress the clock size by directly modulating a distributed Bragg reflector(DBR)laser with 3.4GHz microwave.Moreover,the synchronous phase and polarization modulation are successfully applied to microwave and laser beams respectively,which form the so-called constructive polarization modulation.A CPT atomic clock signal with high contrast(14.7%)and narrow linewidth(416Hz)is obtained.The size,complexity and environmental sensitivity of the clock system are significantly reduced due to the direct modulation,thus it leads to a feasible way to implement a compact and high-performance CPT atomic clock.

Design of Mercury Lamp for Trapped Ion Frequency Standards

WANG Nuan-rang, CHEN Xing, ZHAO Huan, GE Jun

2020, 40(3):  27-30.  doi:10.12060/j.issn.1000-7202.2020.03.06

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the mercury ion trapped microwave frequency standard has the potential applications for the future satellite,deep space explorations and time keeping for its great advantages in the total volume and stability.The high frequency spectrum of mercury ion trapped microwave frequency standard is pumped by the mercury lamp which has small volume and long lifetime,as the base of superiority of mercury ion trapped microwave frequency standard.However,the mercury RF discharge lamp used for optical pumping and state detection may limit the ultimate stability performance of the clock.So we have carried out many experiments to enhance the light stability and the ratio of useful light at 194nm and unwanted background light at 254nm(194/254).Finally,the stability of light power is about 2.5% in 3 days,the 194/254 ratio is about 1/45,and with filter bulb the ratio is about 1/3.The experimental system of mercury ion trapped microwave frequency standard will be introduced and the Hg lamp device is presented with the radiation regime.

Theoretical Analysis on Predicting Clock Difference Using Random Pursuit Strategy

WANG Yu-zhuo, GAO Yuan, XU Qing-hua, ZHANG Ai-min

2020, 40(3):  31-34.  doi:10.12060/j.issn.1000-7202.2020.03.07

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Time always stable elapses forward,which is different from other physical quantities.It determines that only the past time can be accurately measured and evaluated.In order to ensure the accuracy of output signal of time scale at next time,the prediction and control of atomic clock signals is indispensable.This paper analyzed theoretically the running principle,uncertainty evaluation,key parameters’ optimization and other problems of random pursuit strategy to clarify its operational mechanism for predicting clock difference.In addition,we attempted to discuss on the applicability and proposed two new ideas of further study about random pursuit strategy.

Comparing Test for ps Measurements of Homemade Commercial MTIM Meter

ZHANG-Jun, CHEN-Ming, CHEN Hongqing

2020, 40(3):  35-39.  doi:10.12060/j.issn.1000-7202.2020.03.08

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It has been introduced the progress of homemade commercial MTIM meter for ps measurement along with the project development of BeiDou navigation system.At the same time,it has been showed that the statistical data analysis on the measurements of homemade commercial MTIM meter comparing with those foreign well-known MTIM meter among the engineering application of BeiDou system.The comparing results show that the homemade MTIM meter has performed very well as following resolution,<10ps;noise,<15ps;uncertainty,<20ps;temperature coefficient,<1ps/℃.The ps measurement channels counted by hundreds for homemade MTIM meters more than tens have been tested and inspected by user in high standard for one batch production.It comes to a conclusion that homemade commercial MTIM meter is as good as those foreign well-known MTIM equipment.

Application of OPC UA Technology in Intelligent Calibration System

DING Wei, PENG Cheng, LI Jun, HOU Xu-wei

2020, 40(3):  40-45.  doi:10.12060/j.issn.1000-7202.2020.03.09

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With the requirements of high efficiency,high benefit and high quality,the metrology field set more demands on the efficiency of verification and calibration tasks.The continuous innovation and development of artificial intelligence technology provides a new approach for the intelligent measurement methods.In combination with the actual working conditions of the unit,in order to improve the automation degree of the handheld digital multimeter verification system,combined with robots,industrial cameras,sensors and other devices with intelligent technology,a fully automatic calibration system for the handheld multimeter was developed.In view of how to realize secure and stable real-time data interaction between the system host computer based on LabVIEW and the slave computer based on PLC technology,two communication methods based on the traditional technology of creating Shared variables and OPC UA technology were proposed.Through engineering implementation,the feasibility of communication between LabVIEW and PLC based on OPC UA technology was fully verified.This method of communication had the obvious advantages such as shorter development cycle,higher stability,faster response and more strong real-time.At the same time,the programming workload was reduced,the code was more concise and beautiful,and the maintenance difficulty was reduced.

The Influence of Calibration Substrate Boundary Conditions to On-wafer Calibration Standards

HUO Ye, WANG Yi-bang, WU Ai-hua, DU Jing, LUAN Peng, ZHANG Xiao-yun

2020, 40(3):  46-50.  doi:10.12060/j.issn.1000-7202.2020.03.10

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Throught international research of calibration substrate boundary conditions is analyzed.The influence of different calibration substrate boundary conditions on the characteristics and calibration accuracy of coplanar waveguide(CPW)transmission lines is introduced.A multi-line TRL on-wafer calibration standards for W band GaAs substrate was developed,it is placed on metal chuck,glass and absorbing material.After calibrating the system with three calibration standards with different calibration substrates,the attenuation constants,relative permittivity and characteristic impedance of CPW transmission lines are extracted respectively,the short standard and transmission line standard of commercial calibration standards 104-783A are tested to verify the rationality of the results.

Research on Correction Method of Quasi-far-field Antenna Test

KUANG Hao-xin, WANG Xiao-fei, LI Xi, CHEN Hai-ying, CAI Hong-wei

2020, 40(3):  51-55.  doi:10.12060/j.issn.1000-7202.2020.03.11

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Far-field antenna measurement is a common method to obtain antenna radiation characteristics.However,for the antenna with large one dimension and small one dimension,such as the base station antenna,it is often unable to meet the far-field test conditions due to the limitation of site factors,and the near-field measurement is time-consuming and laborious.In this Quasi-far-field condition,the antenna test results are quite different from those in the far-field condition.This paper presents a theoretical calculation method for calculating the far-field pattern from the pattern measured on the distance of the Quasi-far field based on cylindrical wave expansion.The results of the algorithm are in good agreement with the results of the theoretical calculation,and the correctness of the algorithm is verified.

Design and Implementation of Acquiring DME Interrogating Signal

FANG Cheng

2020, 40(3):  56-60.  doi:10.12060/j.issn.1000-7202.2020.03.12

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Acquiring DME interrogating signal is an important part of DME ground equipment.Most of the capture units used in the active ground equipment are designed as separation device circuits,they are complex and difficult to control,high cost of improvement and maintenance.In this paper,ADC and FPGA are used as the main functional devices.It relies on software algorithm to complete digital filtering,pulse peak extraction and half-amplitude calculation,and realizes the recognition and capture of interrogating signal.This scheme not only greatly reduces the number of components and the size of device,but also improves the scalability and reliability.The test results on the cabinet meet the design requirements.

A Feature Extraction and Classification Method of the Vibratory Signal on Ground

CHANG Ke-wu, GUO Hui-jie

2020, 40(3):  61-64.  doi:10.12060/j.issn.1000-7202.2020.03.13

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A method is proposed to detect,identify and warn the excavation and destruction of underground infrastructure in real time,by feature extraction and classification of the vibratory signal on ground.An improved radial basis neural network classification model is constructed by extracting the multi-domain energy joint distribution feature vector of the wavelet packet transform domain and the ensemble empirical mode transform domain,which adopts machine learning methods to extract stable multi-domain fusion features of the target signal and achieve accurate feature classification prediction.It can be concluded from the simulation experiment results of multi-category ground vibratory signals that the algorithm and model proposed in this paper can effectively improve the classification accuracy of the ground vibratory signals and have strong robustness to ground vibratory interference signals.

Research of Neutron Spectrum Unfolding Procedure Using Genetic Algorithm Technique

LI Wei, JIAO Ting-yu, LI Xiao-bo, LIU Yun-tao

2020, 40(3):  65-68.  doi:10.12060/j.issn.1000-7202.2020.03.14

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The main factor of limiting development of neutron spectrum measuring technique is unfolding procedure.Genetic algorithm is one of artificial intelligent algorithm,which is quickly global convergence.This paper discusses the application of genetic algorithm in the region of neutron spectrum unfolding.We develop an unfolding program based on genetic algorithm,and the good results have been achieved in measurement of multi sphere.²⁴¹Am-Be neutron source and ²⁵²Cf neutron source were measured by Bonner Sphere Spectrometer(BSS)using genetic algorithm.Compared with the standard spectrum recommended by ISO8529,the reliability of genetic algorithm is verified.

Study on Additional Filtration of High Energy(450kV)X-ray Reference Radiation Field

XU Yang, GAO Fei, ZHAO Rui, WANG Bo, LIN Min, NI Ning

2020, 40(3):  69-74.  doi:10.12060/j.issn.1000-7202.2020.03.15

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The model of 450kV X-ray tube is established by MCNP code,and the primary X-ray spectrums and mean energy of each reference radiation qualities are calculated.The curve of the relationship between the existing range of tube voltage and the thickness of the additional filtration in ISO 4037-1 is fitted quadratic function to determine the thickness range required for simulation.MCNP code is used to calculate the mean photon energy of each additional filtration combination,and compared with the mean photon energy with extrapolation method.The additional filtration with the smallest relative deviation is taken as the final determined value.From the comparison of simulation and measurement results of some energy points,it can be seen that the mean photon energy obtained by simulation is within 2%,which is consistent with the measurement results of PTB and the National Institute of Metrology,and the maximum relative deviation is 18%.

Weld Defect Detection based on Improved Deep Learning

GU Jing, XIE Ze-qun, ZHANG Xin-yu

2020, 40(3):  75-79.  doi:10.12060/j.issn.1000-7202.2020.03.16

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Aiming at the problem that the traditional Faster RCNN model is not ideal for detecting small defect targets when performing weld defect detection,a weld defect detection algorithm based on improved deep learning Faster RCNN Model is proposed,in which,multi-scale feature maps are extracted through multi-layer feature networks and are used in subsequent parts of the model,to make full use of the low-level features in the model and add detailed information.And then,the region proposal network of the proposed models is improved and a variety of sliding windows is added,thereby improving the aspect ratio of the model anchor point and improving the detection capability.Experiment results show that,the improved Faster RCNN model achieves the best defect detection results and achieves better detection accuracy for small defect targets,verifying the effectiveness of the algorithm.

Application of Ensemble Learning in AOS Protocol Recognition with High Bit Error Rate

ZHU Ming, WANG Chun-mei, YAO Xiu-juan, LI Xue

2020, 40(3):  80-87.  doi:10.12060/j.issn.1000-7202.2020.03.17

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In the face of the transmission characteristics of high bit error rate in space-based networks,and to ensure the efficient and reliable transmission of data between heterogeneous networks,a recognition system method based on integrated learning for AOS(Advanced Orbiting Systems)protocol in spatial link layer is designed.This method uses the integrated learning model to learn the AOS protocol data,constructs the AOS protocol recognition model based on the integrated learning,realizes the AOS protocol recognition accurately,and carries on the experimental verification under the high bit error rate.The experimental results show that the integrated learning model has a good recognition effect in AOS protocol recognition,the recognition efficiency has been improved significantly,and it can still maintain a stable recognition effect at a high bit error rate of 10^-1.

Research on Remote Field Integral Calibration Technology for Radar TR Test System

LOU Hong-ying, YANG Zhong, SHEN Bao-long, CHEN Xiao-jie

2020, 40(3):  88-93.  doi:10.12060/j.issn.1000-7202.2020.03.18

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For the large-scale test system for multi-variety and small-volume product testing in the TR production line,there are some measurement difficulties and problems in quality control,on-site rapid and overall calibration etc.We design standardized and universal on-site delivery standards and standard metering adapters,and establish a remote metering control system,which is supported by the information platform,and overcome the difficulties of remote automatic online measurement of large-scale system-level equipment,and realize the remote automatic field calibration of the radar TR production line test system.

Research on Adjustment Method of Calibration Intervals of Measuring Instruments

WANG Rui-bao, PAN De-xiang

2020, 40(3):  94-100.  doi:10.12060/j.issn.1000-7202.2020.03.19

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In order to select a suitable subsequent calibration interval,the adjustment method of the calibration interval of the measurement instrument is studied through historical calibration data.The methods of calibration parameter value prediction,period prediction,weighted average,etc.,and the development of application software on interval adjustment are analyzed and studied,from the aspects of algorithm description and case analysis,etc.The results show that the methods of parameter value prediction and statistics have high accuracy and complexity; the methods of simple reaction and the improved reaction are simple and easy to implement; the weighted average method is fit to measurement system with multi-parameter,multi-device.Each method has its own characteristics and applicable fields.The adjustment method of calibration intervals should be selected comprehensively according to type,characteristics,quantity of parameters and instruments,characteristics and cost of the calibration process in the actual calibration work.