基于单片机和GPS信号的校频系统

介绍一种基于INTEL 80C196KC单片机的校频系统,包括系统的设计原理、硬件组成和软件实现。该系统通过利用GPS接收机得到的1PPS秒脉冲信号,实现对晶体振荡器频率的校准,从而获得一个短期及长期稳定度都比较优良的时间频率标准。该系统采用了量化时延原理进行短时间间隔比对,对测量数据进行卡尔曼滤波处理。     

基于GPS实现测频等功能的虚拟仪器的研制

设计和研制了一种适用于大专院校示范教学实验的虚拟仪器。该虚拟仪器以GPS接收模块输出的1PPS(秒脉冲)信号为基准,测量无源石英晶体振荡器频率,同时利用GPS信号实现了仪器的时间同步与测距功能。从硬件和软件两方面描述了该虚拟仪器的构成及设计方法,主要介绍和讨论基于GPS和虚拟仪器技术实现多功能测量的途径。     

用于守时系统中的单片机输出监控器的研制

ＭＤ－１输出监控器是一个Ｉｎｔｅｌ８０３１单片机系统，具有时间比对测量、标准时间频率信号隔离输出、监控报警等功能。与ＰＣ微机配合，可建立具有自动守时功能的标准时间工作站，文中介绍了该仪器的软硬件设计     

用于守时系统中的单片机输出监控器的研制

ＭＤ－１输出监控是一个Ｉｎｔｅｌ８０３１单片机系统，具有时间比对测量、标准时间频率信号隔离输出、监控报警等功能。与ＰＣ微机配合，可建立具有自动守时功能的标准时间工作站。文中介绍了该仪器的软件硬件设计。     

基于AD9956的任意频率合成器研制

为满足精密时间测量和高性能星载原子钟等国家重要研究课题的实验应用需求,研制了主要由AD9956芯片和8位高性能单片机构成的一种DDS(直接数字合成)任意频率合成器。在分析DDS的基本原理和特点的基础上,从硬、软件等方面较为详细地介绍了该频率合成器的设计,对同时完成的专用于控制该合成器工作的计算机应用软件也作了介绍。实际使用结果表明:研制的合成器符合实验使用要求,并对促进课题的研究完成发挥了积极作用。     

GPS载波相位测量定位设备的设计与实现

介绍了一种GPS载波相位测量定位设备的设计方案和原理.该设备由MCS-51单片机,摩托罗拉VP 6PS 0EM板,高速CMOS电路,非易失存储器和A/D转换器等组成.该设备具有测 量精度高、能耗低、体积小、重量轻、操作灵活简便、抗干扰能力强、能自动记录长时间测量数据等特点.     

关于使用VFC技术测频的浅析

目前,我们有可能利用 VF 转换技术进行高精度的频率测量,如果把经典比相方法和该技术结合起来,则相位显示的精度将能得到较大的提高,因而频率计数器的±赫误差可被忽略。正因为如此,该方法可进一步扩展经典比相技术的测频精度,所以,这种方法有可能适用于现代原子频标的高精度频率测量。本文讨论了一些有关把检相电压转换为频率以用于测频的有关问题,诸如该方法的基本关系式。主要误差项韵分析和讨论,这又包括了 V—F 转换器件的非线性误差及相位比较系统的噪声电压 Vn,以及系统可能达到的测频灵敏度和该方法的有关一些技术问题。     

基于DSP的小型化高精度频标比对系统研制

针对传统双混频时差法测频的局限性,提出了一种差拍数字化精密频率测量方法,基于正弦差拍技术、同步采样技术和数字信号处理技术设计实现了一种新型频标比对系统,可实现对5MHz、10MHz等频标信号的比对测量。实验结果证明,测量10MHz频标信号时系统本底噪声约为1×10^-12／s。系统拥有测量精度高,体积小以及成本低的特点,在时频测量领域具有良好的推广和应用价值。     

计算机控制的高精度频率源设计

通过对通用串行总线(USB)协议和直接数字合成(DDS)技术的研究和分析,设计实现了一种采用DDS技术的高精度频率源,并且能通过计算机应用软件对其进行实时控制.给出了该设计的硬件结构与部分关键程序的结构,同时给出了对该设计性能参数的测量结果,并对其进行了简单分析和探讨.     

频率稳定度实时评估系统的设计与实现

为了实时计算原子钟的频率稳定度,设计了一种频率稳定度实时评估系统.利用现有理论基础(稳定度测量原理及其算法等)以及软件技术开发了一种实时计算并以图形显示原子钟稳定度的测量分析软件.该软件使用VC++的多媒体定时器实现数据的实时不间断采集及计算,同时采用双缓存绘图技术显示计算结果.测试结果表明该软件工作稳定,计算结果可靠、可信.     

时间间隔计数器的研制

介绍了一种新研制的时间间隔计数器,并给出了实验结果和误差的定性分析。通过斜坡发生器,高速采样保持,A／D转换和器件时延平衡等电路的使用,该计数器在5MHz频标下可达到较高的测量精度和分辨率,该计数器亦可用于频率的精确测量。     

Low Frequency Observations of Pulsars at MRT – Results on a few ‘normal’ pulsars and a ‘millisecond’ pulsar

The MRT pulsar observing system set-up in July 1996 has been used to observe about 30 pulsars at our low observing frequency of 150MHz. From the data considered so far, we have detected 10 pulsars, including the bright millisecond pulsar (MSP) J0437-4715. This is the only MSP observable at such a low frequency making its study specially interesting and more so that it has some apparently unusual properties. In this paper, we discuss some of our main results obtained on the MSP J0437-4715 and on the ‘core-single’ normal pulsarsJ1453-6413 and J1752-2806. Our results are also compared with those obtained at other frequencies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assessing the accuracy of phase equilibrium software in reproducing the liquidus multiple saturation conditions of lunar and Martian basalt compositions

Accurate computational modeling allows the use of software as a first approach to some petrological problems that typically require experimentation, but most programs have not yet been fully tested for accuracy with lunar or Martian melt compositions. The programs pMELTS, MAGPOX, and Perple_X stand out for phase equilibrium modeling, as their calibrations include experiments of lunar compositions or have precise thermodynamic constraints for similar compositions. A set of lunar mare basalts, picritic glasses, and basaltic Martian compositions with known experimentally determined multiple saturation point (MSP) conditions were used here for phase equilibrium modeling. The accuracy of each program was tested through the determination of MSPs on the liquidus of the selected compositions. This point in pressure–temperature space can be considered as a direct proxy of the stable phases and the equilibrium conditions during partial melting of mantle sources. We identify a trend in experimental data between MSP temperature and MgO, CaO, and SiO₂ concentrations, and similar trends are found in model results. However, only Perple_X is able to closely match the experimental data, despite the fact it does not accurately model ilmenite saturation for high-Ti lunar basalts. We find that pMELTS miscalculates olivine saturation for MgO-rich compositions and MAGPOX systematically underestimates MSP pressure and temperatures and can only be used when olivine is the liquidus phase. For modeling lunar or Martian basalt compositions, Perple_X can be used for optimal results, although no software is yet capable of bypassing the need to constrain MSP conditions through experimentation.     

Multiple field line resonances: Optical,magnetic and absorption signatures

We present multi-instrument observations of ultra low frequency (ULF) wave activity from the dawn flank magnetosphere during the period 12:00–13:30 UT on the 16 December 2003. Optical, magnetic and riometer measurements from the Churchill line meridian in the Canadian sector are presented which demonstrate the presence of multiple discrete auroral arc structures accompanied by periodic magnetic and riometer absorption perturbations in the Pc5 (150–600 s) ULF band. Clear polewards propagation is demonstrated in all the instrument data sets, the magnetic signals showing most clearly the amplitude and phase characteristics consistent with discrete frequency field line resonances (FLRs) on closed field lines. Two discrete frequency field line resonant signals are apparent, at 1.8 and 3.0 mHz which resonate at approximately the same latitude. We explain this via the calculation of the Alfvén continuum, and show that both frequencies may be resonant in the same latitudinal region within instrumental resolution. The meridian scanning photometer (MSP) observations from polewards of the magnetometer determined resonant latitudes show evidence of low intensity (∼200 R) poleward moving discrete arcs related to the ULF waves. Interestingly the MSP observations demonstrate poleward phase propagation with variable rates across the field of view; faster apparent polewards phase propagation being seen at higher latitudes. We demonstrate that the complicated “braided” phase of the arcs can be explained via the precipitation resulting from the superposition of two discrete FLRs. Furthermore, we characterise the ≳25 keV energetic electron precipitation in the region of the FLRs and the arc structures via periodic D-region absorption. In this way, we link the magnetic and both soft and energetic particle precipitation signatures of FLRs together for the first time. Our results demonstrate that riometer absorption can be used to characterise FLRs, however, this is only generally possible at lower L-shells where energetic electrons in the ring current overlap with the FLR fields in the equatorial plane.     

NTSC的双混频时差测量系统试运转结果分析

中国科学院国家授时中心(NTSC)新进口的由德国Timetech公司制造的双混频时差测量系统(dual mixer time difference system,DMTD)已经通过了试运行。介绍了DMTD的工作原理和设备结构。NTSC时频基准实验室的主钟(MC)信号作为DMTD的频率参考信号,5个氢钟和18个铯钟的频率信号作为被测信号与MC信号进行相位比对。用频率分配放大器输出的多路MC信号也作为被测信号用以监测DMTD本身的精度和稳定度。给出了DMTD和时间间隔计数器TIC实际测量结果的比较及误差分析。测量结果表明DMTD特别适用于频率短期稳定度非常高的氢原子钟这样的频标之间的频率和时间比对。该设备将用于NTSC的守时工作,不久的将来也将用于铯喷泉与氢钟的频率比对。     

嵌入式时间间隔计数器的研制

介绍了一种新研制的嵌入式时间间隔计数器，它可作为一种功能模块用于用户的设备或时统中，实现高精度时间测量。从基本原理、硬、软件和功能等不同角度对计数器进行了较为详细的讨论。在该计数器的研制过程中还开发了用来调试计数器和供计数器用户使用的计算机应用软件，对此也作了简要介绍。最后，给出了计数器的设计指标和一些实测数据。     

Long-term measurements of 36Cl to investigate potential solar influence on the decay rate

Recently, Jenkins et al. [6] reported on fluctuations in the detected decay events of ³⁶Cl which were measured with a Geiger–Müller counter. Experimental data of ³²Si measured by means of an end-window gas-flow proportional counter at the Brookhaven National Laboratory show similar periodicity, albeit a different amplitude. Jenkins et al. interpret the fluctuations as evidence of solar influence on the decay rates of beta-decaying radionuclides.In this work, liquid scintillation counting was used to check for potential variations in the ³⁶Cl decay rates. A custom-built counter with three photomultiplier tubes was used. In contrast to commercial counters, the relevant parameters of our system are well controlled and the discrimination threshold and HV setting can be adjusted and checked. The experimental data were analyzed by means of the triple-to-double coincidence ratio (TDCR) method which is a primary method for activity determination. Thus, our results do not depend on any other standard or reference source.Our data show fluctuations which are by more than one order of magnitude lower than those seen in the experiment using a Geiger–Müller counter. More importantly, no oscillation could be identified. Interestingly, our data overlap in time with those from Jenkins et al. [6]. We do not observe the phase and amplitude as seen by Jenkins and conclude that the fluctuations are not due to solar influence. This also implies that the interpretation by Jenkins et al. is false.     

Numerical Evaluation of the General Yarkovsky Effect: Effects on Eccentricity and Longitude of Periapse

J. N. Spitale and R. Greenberg (2001, Icarus149, 222-234) developed a nonlinearized, finite-difference solution to the heat equation that yields orbital rates of change due to the Yarkovsky effect for small, spherical, bare-rock asteroids and used it to investigate changes in semimajor axis caused by the Yarkovsky effect. Here, we present results for changes in eccentricity and longitude of periapse. These results may be useful as benchmarks for simplified analytical solutions. Moreover, we explore a range of parameters, some of which are inaccessible to most other approaches. Instantaneous rates can be quite fast: For a 1-m scale body rotating with a 5-h period, de/dt can be as fast as 0.1 per million years (da/dt rates for similar test bodies were reported in J. N. Spitale and R. Greenberg (2001, Icarus149, 222-234)). For more typical rotation periods, these rates would be considerably slower. Output from our calculation method could be used in simulations of asteroid population evolution such as that by W. F. Bottke, D. P. Rubincam, and J. A. Burns (2000, Icarus145, 301-331). On long time scales, impacts would randomize the spin axis before significant orbital evolution could occur. Nevertheless, occasional favorable rotation states might persist long enough for substantial eccentricity changes to accumulate (1) if the body is decoupled from the main belt (e.g., many near-Earth asteroids), (2) if the population of very small (mm-scale) main-belt impactors is less than expected, or (3) if our numerical results are scaled up to km-size bodies.     

基于GPIB接口的计数器数据采集与控制软件

在Windows平台上 ,使用VC 6 .0开发了一套基于GPIB接口的计数器数据采集与控制软件 ,其特点是采用了多线程机制 ,可实现对计数器的控制 ,以及数据的采集与实时显示。