A digital signal conversion system for astronomy radio interferometers with small antennas

Results of designing a digital signal conversion system for radio interferometers with small-diameter (up to 12 m) antennas are presented. The system contains four digital signal conversion channels with 500-MHz bandwidths. The output data stream rate in the VDIF format is 2048 Mbit/s per channel, and the cumulative output data flow is 8192 Mbit/s. The observation data flows arrive at the signal recording buffer unit and can be transmitted from there via a 10G Ethernet interface to a correlator in near-real time.     

A digital radio interferometric data acquisition system

Results of designing a P1002M 16-channel digital radio interferometric signal conversion complex, which records data with a rate of up to 2048 Mbit/s in the VSI-H format, are presented. The frequency band varies from 100 to 1000 MHz. The bandwidths vary from 0.5 to 32.0 MHz. The P1002M system is compatible with analog data acquisition systems installed on radio telescopes of the Kvazar-KVO complex. The manufactured P1002M prototype is intended for installing on a PT-70 radio telescope (town of Ussuriisk).     

A digital signal converter for radio astronomical systems

A digital signal converter operating in a video frequency band (up to 32 MHz) and intended for radio astronomical equipment is based on an LTC2288 analog-to-digital converter and an XC4VSX25 field programmed gate array. A two-band base band converter improving parameters of the radio interferometric terminal, a two-channel spectrometer minimizing times of observation of radio-frequency sources in spectral lines, and a radiometer for recording signals in a continuum operating under the action of radio interference have been designed using the converter. The advantages of this equipment are confirmed by results of tests at the Svetloe radio astronomical observatory.     

A Data Acquisition System for Very-Long-Baseline Interferometers

A data-acquisition system designed for very-long-baseline interferometers is connected to the outputs of cryoelectronic radio astronomy receivers, selects signals in specified frequency bands, and converts them into digital data flows for their recording or transmission through telecommunication channels. The system has two inputs and may contain from two to eight base-band converters with an intermediate frequency tuning range of 100–1000 MHz with a 10-kHz step. These converters transform input signals into video frequencies (up to 16 MHz) and separate signals of the upper and lower side bands with an image rejection of >23 dB. The distortions and loss in the phase coherence of the received noise signals are minimized thanks to the equalizing of the amplitude and phase responses of the amplifiers and selectors, and the good spectral characteristics of the local oscillators of the base-band converters. The data-acquisition system is controlled by a PC or the Mark IV Field System program (now used internationally in the pursuit of radio interferometry), which is installed in the radio telescope's central computer using an RS-232 interface. The prototype of such a system is used as standard equipment for conducting observations on the Svetloye–Zelenchukskaya radio interferometer. The first lot of such systems for the development of a network of radio interferometers has been produced.     

射电天文中大型望远镜阵列研究

射电干涉技术的提高以及大型射电望远镜阵列的出现为射电天文观测提供了很高的空间分辨率和灵敏度,极大地推动了天文学的发展.文中简要回顾了射电望远镜的发展历程,重点介绍了国内外著名的大型射电望远镜阵列及其在射电观测领域的重要作用,并分析了射电望远镜阵列的布阵方式以及单元望远镜中天线馈源的型式.     

A portable instrument for automatic detection and classification of telecommunication signals

In this paper, a new portable instrument for the analysis of telecommunication signals is proposed, which is able to: (i) observe a wideband in which even multiple signals can be present at different carrier frequencies; (ii) divide the observed wideband in smaller sub-bands and detect the presence of a signal in each sub-band; and (iii) recognize the modulation type of the detected signals, among the most common digital schemes, without requiring any knowledge about their parameters.The proposed instrument, completed with the signal-dependant measurement routines, represents a considerable advancement of the research among the instruments for telecommunication systems, as it is capable of working autonomously on unknown signals. Such feature avoids both the intervention of a skilled operator in setting up the measurement task, and make it ready to be used in the next generation telecommunication scenarios, where a more flexible use of the radio spectrum and a dynamic allocation of users are foreseen. The hardware architecture is based on a PXI data acquisition system and a laptop PC processing unit while the control software has been developed in LabVIEW. The paper proposal has been validated using actual signals in several scenarios emulating real world communications.     

Impact of plasma noise on a direct thrust measurement system

In order to evaluate the accuracy and sensitivity of a pendulum-type thrust measurement system, a linear variable differential transformer (LVDT) and a laser optical displacement sensor have been used simultaneously to determine the displacement resulting from an applied thrust. The LVDT sensor uses an analog interface, whereas the laser sensor uses a digital interface to communicate the displacement readings to the data acquisition equipment. The data collected by both sensors show good agreement for static mass calibrations and validation with a cold gas thruster. However, the data obtained using the LVDT deviate significantly from that of the laser sensor when operating two varieties of plasma thrusters: a radio frequency (RF) driven plasma thruster, and a DC powered plasma thruster. Results establish that even with appropriate shielding and signal filtering the LVDT sensor is subject to plasma noise and radio frequency interactions which result in anomalous thrust readings. Experimental data show that the thrust determined using the LVDT system in a direct current plasma environment and a RF discharge is approximately a factor of three higher than the thrust values obtained using a laser sensor system for the operating conditions investigated. These findings are of significance to the electric propulsion community as LVDT sensors are often utilized in thrust measurement systems and accurate thrust measurement and the reproducibility of thrust data is key to analyzing thruster performance. Methods are proposed to evaluate system susceptibility to plasma noise and an effective filtering scheme presented for DC discharges.     

A Data Stream Converter for a Radio Telescope with a Wideband-Signal Digital Recording System

A data-stream converter makes it possible to connect a radio telescope with wideband (512 MHz) signal-recording channels to active very-long-baseline interferometers using multichannel recording systems for narrowband (16 or 8 MHz) signals. A digital converter based on a field programmed gate array (FPGA) selects and formats up to 16 narrowband signals.     

Controller-area-network bus control and monitor system for a radio astronomy interferometer

We describe the design and implementation of a controller-area-network bus (CANbus) monitor and control system for a millimeter wave interferometer. The Combined Array for Research in Millimeter-wave Astronomy (CARMA) is a 15-antenna connected-element interferometer for astronomical imaging, created by the merger of two university observatories. Its new control system relies on a central computer supervising a variety of subsystem computers, many of which control distributed intelligent nodes over CANbus. Subsystems are located in the control building and in individual antennas and communicate with the central computer via Ethernet. Each of the CAN modules has a very specific function, such as reading an antenna encoder or tuning an oscillator. Hardware for the modules was based on a core design including a commercial CANbus-enabled single-board computer and some standard circuitry for interfacing to peripherals. Hardware elements were added or changed as necessary for the specific module types. Similarly, a base set of embedded code was implemented for essential common functions such as CAN message handling and time keeping and extended to implement the required functionality for the different hardware. Using a standard CAN messaging protocol designed to fit the requirements of CARMA and a well-defined interface to the high-level software allowed separate development of high-level code and embedded code with minimal integration problems. Over 30 module types have been implemented and successfully deployed in CARMA, which is now delivering excellent new science data.     

A waveform digitizer-based automatic modulation classifier for a flexible spectrum management

The paper presents the development and validation of an automatic digital modulation classifier based on a waveform digitizer architecture. The proposed automatic digital modulation classifier can be used for signal recognition in the next generation telecommunication systems, characterized by a flexible and dynamic management of the radio spectrum. It has been implemented on a PC architecture, connected with two different types of waveform digitizers. The experimental validation has been carried out by means of actual telecommunication signals, even in presence of narrowband and wideband interference.     

模拟主用户攻击情况下的压缩宽带频谱感知

由于ADC采样速率的限制,特别是在恶意用户试图模拟主用户(PU)以阻止次用户(SU)接入空闲授权频谱的情况下,使得认知无线电网络(CRN)中的宽带频谱感知技术面临着极大的技术挑战。针对这些问题,本文提出一种基于随机矩阵理论的压缩宽带频谱感知方法(RMT-CWSS)。RMT-CWSS算法利用随机矩阵理论直接对压缩观测数据进行处理,无需重构出原信号即可实现对宽带频谱进行感知。同时,为了减轻次用户在数据获取和频谱感知过程中的开销,本文提出一种基于传感器节点(SN)辅助感知的合作频谱感知架构。理论分析与仿真结果表明,在存在恶意用户模拟主用户进行攻击的情况下,与传统的基于RMT的宽带频谱感知方法相比,该算法具有复杂度更低、感知性能更好、更稳定等优点。     

A correlator for the quasar VLBI network

A correlator corresponding to the modern requirements for processing very long baseline interferometer (VLBI) observation data has been developed at the Institute of Applied Astronomy, Russian Academy of Sciences (IAA RAS) for the Quasar VLBI network. The correlator can process data flows of up to 1 GB/s from each station. The maximum numbers of simultaneously processed stations and baselines are 6 and 15, respectively. The correlator is equipped with Mark5B playback systems, thus allowing quasi-real time VLBI session processing. The XF processing algorithm is implemented in the hardware-software correlator. Hardware is used to calculate cross-correlation functions and extract calibration signals of the picosecond-pulse generators of stations. At present, the correlator is used to process all VLBI observations of the Quasar network performed according to national programs.     

Surface electrode switching of a 16-electrode wireless EIT system using RF-based digital data transmission scheme with 8 channel encoder/decoder ICs

A Radio Frequency (RF) based digital data transmission scheme with 8 channel encoder/decoder ICs is proposed for surface electrode switching of a 16-electrode wireless Electrical Impedance Tomography (EIT) system. A RF based wireless digital data transmission module (WDDTM) is developed and the electrode switching of a EIT system is studied by analyzing the boundary data collected and the resistivity images of practical phantoms. An analog multiplexers based electrode switching module (ESM) is developed with analog multiplexers and switched with parallel digital data transmitted by a wireless transmitter/receiver (T_x/R_x) module working with radio frequency technology. Parallel digital bits are generated using NI USB 6251 card working in LabVIEW platform and sent to transmission module to transmit the digital data to the receiver end. The transmitter/receiver module developed is properly interfaced with the personal computer (PC) and practical phantoms through the ESM and USB based DAQ system respectively. It is observed that the digital bits required for multiplexer operation are sequentially generated by the digital output (D/O) ports of the DAQ card. Parallel to serial and serial to parallel conversion of digital data are suitably done by encoder and decoder ICs. Wireless digital data transmission module successfully transmitted and received the parallel data required for switching the current and voltage electrodes wirelessly. 1 mA, 50 kHz sinusoidal constant current is injected at the phantom boundary using common ground current injection protocol and the boundary potentials developed at the voltage electrodes are measured. Resistivity images of the practical phantoms are reconstructed from boundary data using EIDORS. Boundary data and the resistivity images reconstructed from the surface potentials are studied to assess the wireless digital data transmission system. Boundary data profiles of the practical phantom with different configurations show that the multiplexers are operating in the required sequence for common ground current injection protocol. The voltage peaks obtained at the proper positions in the boundary data profiles proved the sequential operation of multiplexers and successful wireless transmission of digital bits. Reconstructed images and their image parameters proved that the boundary data are successfully acquired by the DAQ system which in turn again indicates a sequential and proper operation of multiplexers as well as the successful wireless transmission of digital bits. Hence the developed RF based wireless digital data transmission module (WDDTM) is found suitable for transmitting digital bits required for electrode switching in wireless EIT data acquisition system.     

A novel approach for realization of primary vibration calibration standard by homodyne laser interferometer in frequency range of 0.1 Hz to 20 kHz

The paper discusses the primary vibration calibration standard of NPL, India capable of calibrating the reference accelerometers in frequency range from 0.1 Hz to 20 kHz as per ISO 16063-11. The excitation subsystem produces constant vibration at a specified amplitude and frequency, while the measurement system uses NI interface for measuring the quadrature output. The acceleration level and voltage level at the calibration frequency f is determined by applying a Discrete Fourier Transform to the voltage and displacement signals, and then examining the spectral component at frequency f. A PC-based data acquisition system acquires the accelerometer voltage signal and analog quadrature interferometer photodetector signal pair as well as a digital quadrature pair whereby the software processes the demodulated photodetector signals to reconstruct the armature displacement. The validation of the calibration results for standard reference accelerometers with manufacturer results and uncertainty in calibration in entire frequency range 0.1 Hz to 20 kHz is reported in the present work.     

基于LORA无线通信的数字开关量数据传输

针对钢铁企业现有设备分散、环境恶劣、综合布线复杂等开关数字量采集困难问题,同时为解决因电磁干扰等外界不可控因素导致无线数据传输中数据丢包实际问题,提出基于LORA无线通信可靠握手协议的数字开关量数据传输。采用光电耦合及电路滤波技术提高开关量采集准确性;以SX1278无线电路作为数据传输载体提高点布设传输灵活性;采用可靠握手协议提高数据传输可靠性。实验证明,该设计具有高可靠性与点布设灵活性特性。     

An equivalent time temperature mapping system with a 320 x 256 pixels full-frame 100 kHz sampling rate

In this paper we describe a novel temperature mapping system based on a standard infrared camera with 50 Hz frame rate for the measurement of ultrafast temperature transients which, in principle, demand for a much faster acquisition rate. In particular, we base our system on the widely used equivalent time sampling concept which can be adapted to the temperature acquisition system, thanks to a very fast and sensitive camera sensor: an InSb sensor, which allows a reduced integration time of 10 micros, and a custom digital synchronization circuit. The latter has been realized by the usage of a fully programmable digital circuit, which generates all the signals needed for the synchronization of the IR camera, of the experiment, and a personal computer needed for data acquisition and storage. We show, with experiments, how this system is capable of detecting temperature transients with an equivalent bandwidth of 100 kHz full frame, far beyond the capabilities of the fastest available IR cameras.     

Construction of an Inexpensive Subnanosecond Fluoriheter Using a Microcomputer

ABSTRACT

We describe a simple construction of a data acquisition system using an APPLE 11+ Microcomputer. The system uses a commercially available plug-in Interface board containing an analog/digital converter, a digital/analog converter, and a user dedicated 6522 Versatile Interface Adaptor (VIA). The microcomputer controls the time base and digitizes the vertical output of a sampling oscilloscope through the Interface card. Software has been developed for the data acquisition and manipulation. The system was applied to the determination of subnanosecond fluorescence lifetimes. It is pointed out that the system can be very versatile as a data acquisition and manipulation system despite its lower cost.     

Construction of a new unclipped digital correlator for quasielastic light scattering

An unclipped digital correlator that we have built has been described. Our digital correlator can be easily incorporated (with only a moderate cost) in an established light scattering laboratory equipped with a computer.     

天文光干涉技术

望远镜技术和光干涉技术的结合是提高望远镜分辨率的方法之一。介绍了天文光干涉的原理和实现恒星光干涉主要的几个关键技术,星光采集的定天镜系统、光程补偿的延迟线系统、光束平行性调整的星光方向矫正系统和计算机全自动控制系统,简要介绍光学综合孔径干涉成像技术、天文光干涉的研究状况和天文光干涉技术的发展方向。     

一种方位及俯仰可调控制平台的实现

微波接收机是射电望远镜中专门用于接收射电信号的设备,而强度校准的目的是将接收到的射电信号响应等效地转换为天文意义上的流量密度。由于毫米波校准还易受到大气吸收作用,因此对大气不透明度的测试尤为重要。文中通过搭建机械转动平台及其控制系统,可以精确实现7 mm 波段常温接收机在目标方位下进 行0°~ 90°俯仰扫描观测。通过控制软件并行记录在不同仰角下的接收机输出功率,结合大气辐射转移方程,采用非线性最小二乘拟合的方式,最终得到当前方位7 mm 波段实时的大气不透明度值,很好地实现了精确控制及自动测试功能。