Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.     

An intercontinental array--a next-generation radio telescope

It is difficult to estimate accurately the cost of constructing a large scientific instrument that involves many techniques. On the other hand, most of the component parts of the VLBA consist of antennas and electronic systems that already exist or are being fabricated. The kind of 25-m antennas being constructed for the VLA will cost about $900,000 each and will work at wavelengths as short as 1 cm. A multifrequency radiometer, hydrogen maser frequency standard, small control computer, control building, and wide-band instrumentation recorder bring the cost to about $1.5 million per element, or $15 million for a ten-element array using tape recorders. A multistation playback facility, with ten recorders and enough correlators to handle all interferometer pairs simultaneously, together with the necessary computers to control the processor and reduce the data, may add $5 million. The total cost is thus about $20 million at current prices, including an adequate supply of magnetic tape. This is comparable to the cost of existing large radio telescopes and arrays. An array that used a geostationary communication satellite to transmit the data to a real-time correlator would cost $30 million to $50 million more, but this is still within the price range of other space astronomy projects. It is thus feasible to construct at reasonable cost an intercontinental very long baseline array which has sub-milliarcsecond resolution. This would complement the Very Large Array now being constructed (4), which is much more sensitive to objects of low surface brightness. This next step would permit the study of the universe with unprecedented angular resolution.     

Precision Geodesy via Radio Interferometry

Very-long-baseline interferometry experiments, involving observations of extragalactic radio sources, were performed in 1969 to determine the vector separations between antenna sites in Massachusetts and West Virginia. The 845.130-kilometer baseline was estimated from two separate experiments. The results agreed with each other to within 2 meters in all three components and with a special geodetic survey to within 2 meters in length; the differences in baseline direction as determined by the survey and by interferometry corresponded to discrepancies of about 5 meters. The experiments also yielded positions for nine extragalactic radio sources, most to within 1 arc second, and allowed the hydrogen maser clocks at the two sites to be synchronized a posteriori with an uncertainty of only a few nanoseconds.     

农业机械收音机模块设计

以STC12C5624AD单片机为主控芯片,设计出农业机械收音机模块;利用I2C总线通信,控制收音芯片TEF6606的相对应的寄存器实现3种频段的数字立体声收音功能,并实现自动存台,手动存台,自动搜台以及手动搜台功能。该收音机抗振性强,操作简单,适合安装于农业机械。     

2.4GHz无线信号在苹果园中的衰减模型

为解决苹果园中无线传感器网络的规划和部署问题,研究2.4GHz无线信道在苹果园中的传播特性。在山东省肥城市普通的苹果园进行实地试验。选取对信号传播影响最大的一列果树,发射天线固定在两棵树之间发射信号,分别测量6个高度18个位置点的接收信号强度和丢包率。回归分析结果表明:无论发射天线多高,不同水平高度上的接收信号强度衰减均符合对数路径损耗模型,拟合的决定系数为0.927~0.987。发射天线高度不变时,衰减系数n值能用接收天线高度的二次函数曲线拟合,拟合的决定系数为0.71~0.89;模型参数A和接收天线高度符合线性关系,拟合的RMSE为0.2~1.2。建立以发射天线高度、接收天线高度和传播距离为参数的衰减模型并进行验证试验,结果表明:RMSE为2~5,94%的R2值大于0.9,预测模型能较好的估算收发天线高度不同时的信号强度损耗。     

渔用声纳电子示位标防盗技术研究

针对我国金枪鱼捕捞渔船上的无线电示位标装备现状,特别是为了防止盗取设备强占渔场的现象发生,对带有预警防盗功能的声纳示位标技术展开研究与试验,系统将渔用声纳与卫星电子浮标整体集成,利用水声数据采集技术与卫星数据通信技术,通过水下拾音器采集柴油机噪声的音频信息,该系统集成了卫星定位、声纳探测、无线电与卫星通讯,并开发出了嵌入式防盗设备,系统实现了示位标常规功能的同时增加了有效的预警防盗功能。可以提高我国金枪鱼鱼群探测信息化水平并保证设备的安全性。初步试验结果显示试验选用的渔民标准配备的挂机螺旋桨启动时的频率值稳定在8.5 kHz左右,且空蚀效应明显,在海洋噪声普遍高于10.3 kHz的环境下,嵌入式防盗系统在50~100 m范围内可准确实现设备的预警防盗,且抗干扰能力强,相比于其它防盗方式更为实时有效。     

实现以RFID卡仿真磁卡的模块设计

设计一种能从射频识别(RFID)卡读取数据,而后又仿真磁卡格式输出的模块,借助这种模块,能在不改变原有应用系统的基础上,将系统的磁卡替换为RFID卡.本文介绍的模块选择H4001作为替代磁卡的RFID卡,模块本身则主要由天线、非接触式射频卡读写基站芯片U2270B和单片机AT89C2051构成.在介绍应用电路的同时,分析了RFID卡、磁卡的相关编码格式,提出实现RFID卡信息读取、磁卡仿真输出的方法和步骤,并给出了相应的程序流程图.     

Pioneer 6: Measurement of Transient Faraday Rotation Phenomena Observed during Solar Occultation

Pioneer 6, which was launched into orbit around the sun on 16 December 1965, was occulted by the sun in the last half of November 1968. During the period in which the spacecraft was occulted by the solar corona, the S-band telemetry carrier underwent Faraday rotation as a result of this anisotropic plasma. The NASA-Jet Propulsion Laboratory 210-foot (64-meter) antenna of the Deep Space Network at Barstow, California, which was equipped with an automatic polarization tracking system, was used to measure this effect. Three large-scale transient phenomena were observed. The measurement of these phenomena indicated that Faraday rotation on the order of 40 degrees occurred. The duration of each phenomenon was approximately 2 hours. These phenomena appear to be correlated with observations of solar radio bursts with wavelengths in the dekametric region.     

轻型遥控人工林集材索道遥控器的研究与应用

本文主要论述了以数字锁相频率合成技术为基础的轻型遥控人工林集材索道无线电遥控器的工作原理及其在集材生产中的应用．     

基于 RFID 的茶叶物流追溯系统

利用Coogle公司开发的GoogleMaps,构建了一套基于射频识别技术（RFID）的茶叶物流追溯系统,确保茶叶在生产、加工、销售过程中实物流与信息流的“无缝”对接．消费者可通过浏览器直观地获得所购茶叶的相关信息．     

浅议TD-SCDMA技术及应用

作为第三代移动通信(3G)三大主流技术之一的TD-SCDMA标准,是由中国第一次提出并在无线传输技术(RTT)的基础上与国际合作完成的,标志着拥有中国自主知识产权移动通信标准的诞生。综述了TD-SCDMA使用的智能天线、软件无线电、接力切换等国际领先技术,并指出了存在的问题和解决途径。     

数字化防伪溯源技术在农资监管中的应用

农资是现代农业发展的物质基础,农资质量的有效监管是农民持续增收的重要保障。文章在阐述中国农资市场发展现状的基础上,提出了农资防伪溯源的关键技术——数字化防伪技术。从物联网技术角度出发,阐述了以无线射频识别技术和条形码技术为代表的数字化防伪溯源技术的工作原理及其在农资监管领域的应用。通过对数字防伪技术与传统防伪技术的功能特性进行比较,分析了国内农资防伪技术的未来发展趋势,提出了促进国内农资数字化防伪溯源技术发展的对策和建议。     

基于STC89C58RD-I-芯片的无线多点温度采集系统设计

用新一代STC89C58RD＋单片机、射频芯片nRF401和单总线数字温度传感器DS18820构建无线多点温度采集系统。该系统硬件电路简单,响应速度快,性能稳定,无线通讯距离可达500—800m。     

Planetary radio astronomy observations from voyager 1 near saturn

The Voyager 1 planetary radio astronomy experiment detected two distinct kinds of radio emissions from Saturn. The first, Saturn kilometric radiation, is strongly polarized, bursty, tightly correlated with Saturn's rotation, and exhibits complex dynamic spectral features somewhat reminiscent of those in Jupiter's radio emission. It appears in radio frequencies below about 1.2 megahertz. The second kind of radio emission, Saturn electrostatic discharge, is unpolarized, extremely impulsive, loosely correlated with Saturn's rotation, and very broadband, appearing throughout the observing range of the experiment (20.4 kilohertz to 40.2 megahertz). Its sources appear to lie in the planetary rings.     

Quasi-stellar objects: possible local origin

Many difficulties face the conventional interpretation of the red shift of quasars as a Hubble shift, with associated immense distances. These objects are not of galactic size or nature, and are not associated with galaxies or clusters of galaxies. The continuing energy source for such enormous powers for a period of 10(6) to 10(7) years has not been clearly revealed. The absence of the expected absorption for the Lyman-alpha spectral line of hydrogen is a new difficulty. Because of the relativistic limit on the diameter which can produce rapid fluctuations of light output, there may not be enough surface to radiate the required light.A similar and perhaps more serious difficulty exists for the fluctuating radio output. Calculations given here for synchrotron radiation self-absorption lead to a reasonably accurate formula for the angular diameter of a radio source. For the quasar 3C 273B these relations indicate a conflict with the usually assumed distance. However, the discrepancy may be explained in terms of strong variation of radio diameter with frequency. For CTA 102 the conflict is more serious, and could be explained -for cosmological distance-only by rejecting the data of Sholomitskii. These difficulties are removed by the hypothesis that the observed quasars were ejected from a gravitational collapse at the center of our own galaxy, which may have occurred roughly 5 million years ago. The resultant distances, of the order of a million lightyears, reduce the energy problem by a factor of 10(6) or 10(7). On this basis the optical diameter would be less than a light-hour, about the size of the earth's orbit. A rotating mass of a few thousand solar masses with this diameter would account for the unusual line width, could easily produce the required radiated energy, and could readily account for observed short fluctuation periods and variations in spectrum. It is suggested that the radio output may be produced by high-speed passage of the quasar through intergalactic gas. This would probably correspond to a radio size of a few light-years or less, in agreement with the fluctuations. Since the radio power would be considerably less than that of radio galaxies, it is suggested that radio galaxies may have ejected groups of quasars. This would explain the peculiarly distant locations of the radio sources for many such galaxies. The objections to this model that have been raised are apparently not fatal. In particular, the receding hydrogen cloud discovered by Koehler to be in the line of sight to 3C 273 is more plausibly interpreted as having been ejected from our own galaxy, in the manner observed for other galaxies, than as being associated with the Virgo cluster of galaxies. The latter interpretation, which would place 3C 273 further away, is in conflict with Lyman-alpha absorption data for 3C 9 and other quasars. Thus the local model seems to give a reasonable explanation not only of quasars but also of radio galaxies, bothv of which seem largely to defy explanation on other grounds. Whether or not this model is valid, it is clear that an understanding of quasars will radically change our understanding of the universe.     

Voyager planetary radio astronomy at neptune

Detection of very intense short radio bursts from Neptune was possible as early as 30 days before closest approach and at least 22 days after closest approach. The bursts lay at frequencies in the range 100 to 1300 kilohertz, were narrowband and strongly polarized, and presumably originated in southern polar regions ofthe planet. Episodes of smooth emissions in the frequency range from 20 to 865 kilohertz were detected during an interval of at least 10 days around closest approach. The bursts and the smooth emissions can be described in terms of rotation in a period of 16.11 +/- 0.05 hours. The bursts came at regular intervals throughout the encounter, including episodes both before and after closest approach. The smooth emissions showed a half-cycle phase shift between the five episodes before and after closest approach. This experiment detected the foreshock of Neptune's magnetosphere and the impacts of dust at the times of ring-plane crossings and also near the time of closest approach. Finally, there is no evidence for Neptunian electrostatic discharges.     

Callisto: disk temperature at 3.71-centimeter wavelength

We observed the radio emission of Callisto with a three-element interferometer at the time of the 1973 opposition of Jupiter. Special care was taken to remove the residual, unresolved contribution from Jupiter itself in the antenna side lobes. The resulting disk temperature at a wavelength of 3.71 centimeters, assuming a radius of 2500+/-75 kilometers for Callisto, was 101 degrees +/-25 degrees K. This temperature is much more consistent with emission from a simple dielectric sphere than the considerably higher temnperatures that have been reported for wavelengths of 3.5 and 8.2 millimeters.     

Advance of Study on Design Methods of Hydraulic System of Radio Remote Control of Construction Machinery

The working principle of radio remote controlling of construction machinery should be that signals of the radio wave from the transmitter obtained in the receiver were controlled and then changed into electronic analog or digital signals which can be used to drive different actuators and mechanisms of the vehicle. The vehicle could be acted by following the controlling instructions sent by the operator. The best operation mode of construction machinery is suitable not only to manual operating but also to remote controlling in the same vehicle. The design methods of the hydraulic system used for the radio remote controlling of construction machinery are discussed. The design methods of hydraulic circuits for the actuators controlled by solenoid on-off type valves ,hydro-electronic multi-way proportional valves,closed loop proportional servo driver or threeway proportional reducing valves are discussed in detail (with real example). The design methods of the power shift transmission of electro-hydraulic controlling,the devices of braking and the directional streering are discussed in this paper.     

The upgraded arecibo observatory

Arecibo Observatory's giant spherical reflector antenna has undergone a massive upgrading over the past 3 years. The surface of the reflector has been replaced with aluminum panels to obtain an accuracy of 3.2 mm r.m.s. over the reflector surface. The superstructure has been stabilized and modified to permit operation at S-band frequencies. A high-power S-band radar transmitter has been added to the existing UHF system. These additions and improvements provide the observatory with new and promising research capabilities in the fields of radio and radar astronomy.     

数字孪生系统在农业生产中的应用探讨

数字孪生技术与农业的深度融合将为农业数字化转型升级提供新动能。农业数字孪生系统基于农业生产系统所产生的数据流，通过实时态势感知、超实时虚拟推演和全程交互反馈，有效实现对作物生产系统的智慧管控。系统分析了作物生产系统及其认知方法的发展历程，明确了农业数字孪生系统产生的背景、概念、内涵、基本组成及其技术优势，提出我国农业数字孪生系统的应用方向和发展路径，为推进我国作物生产智能化提供参考。