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 multifunctional digital converter for radio-astronomy signals with a bandwidth of up to 512 MHz

A multifunctional digital signal converter is described, which is used as a channel for the digital conversion and formatting of radio-interferometric signals with bandwidths of up to 512 MHz. The converter allows changes in its function by only a change in the control program, which is administered by the radio-telescope computer. The multifunctional computer can be used for radiometric and spectral measurements and for tests of the receiving–amplifying equipment of the radio telescope.     

一种简易逻辑分析仪的设计

为减低成本,本文介绍了一种基于MCS-51系列单片机和普通示波器组成的简易逻辑分析仪。它采用D/A转换器产生16级输入信号的门限电压,输入信号通过单片机中进行采集、存储、处理,再通过D/A分时输出,同时多踪显示在示波器上。     

Electrometric direct current I/V converter with wide bandwidth

A principle of operation and electrical characteristics of a high frequency current-to-voltage (I/V) converter are presented. The I/V converter measures the electric current with selectable gains of 10(5), 10(4), and 10(3) V/A in the frequency range from DC to 500 kHz, 1.2 MHz, and 2.4 MHz, respectively. These properties make this I/V converter suitable for wide range of applications such as tuning forks, torsion oscillators, ultrasound transducers measurements, detection of the piezoelectric transducers used in STM techniques, etc., in low temperature physics. The influence of the input impedance of a I/V converter on the precision of alternating current measurements is also discussed.     

基于CAV424的电容式液位检测系统

介绍一种基于CAV424的电容式液位检测系统。根据电容式液位传感器的工作原理,传感器两个极板间的电容值会随液位的改变而改变,系统利用电容/电压转换芯片CAV424将电容值转化为电压值输出,然后使用16位高精度∑-△模数转换器AD7705再将电压值转换为数字信号,交由单片机对数据做进一步的处理,如数码管显示及电流输出。电流输出部分由12位串行数模转换器AD7943和4~20mA的电压/电流转换器组成。系统具有RS-485远传接口。     

数模转换过程中的频谱失真及其校正方法

建立了D／A转换器的数学模型，分析了D／A转换器将数字信号转换为模拟信号时产生的频谱失真，导出了频率补偿网络的传递函数，利用频率采样法设计了FUR型频率补偿数字滤波器，给出了校正实例。     

Examples of image processing using a computer controlled SEM

Several examples of the use of digital image processing on SEM images are presented. The emphasis is on image enhancement as opposed to pattern recognition. Examples given include non-linear histogram modification, noise filtering, and frame by frame subtraction. Image processing is done on digitally stored images obtained from a modified SEM. The SEM has been modified to allow minicomputer control of the electron/CRT beam position and blanking. Digitization of the sample signals, such as secondary electron, backscattered electron, and absorbed current is done using a 5 MHz voltage to frequency converter and a 100 KHz timer/sealer combination. Software for image storage and manipulation is also described.     

An 80-MHz, 14-bit bandpass mash sigma–delta/pipeline A/D converter with 5 MHz bandwidth for third generation mobile communication systems

In this paper a bandpass MASH (multi-stage noise shaping) sigma-delta (ΣΔ) modulator is presented. A SNR (signal to noise ratio) of at least 85 dB (equivalent to a resolution of 14 bits) has been achieved over a 5 MHz band around an intermediate frequency (IF) of 20 MHz using a clock frequency of 80 MHz. This performance is obtained using a sixth order bandpass ΣΔ modulator followed by a 10 bit pipeline converter. The proposed circuit has been extensively simulated, both at behavioral and at circuit level, and results are reported.     

An introduction to the mixed-layer probe

The paper describes a free-falling mixed-layer (ML) probe to measure depth, temperature, conductivity, horizontal water velocity gradient (shear) and solar radiation. Measurement effects introduced by the probe tilt and orientation are resolved using a flux-gate compass and a two-axis inclinometer. Sampling of all channels is carried out 50 times/s and the probe drop speed is 1 m/s. Raw data are acquired at depth intervals of 0.02 m and post-processed to give averaged values over 0.10 m scales. The probe is designed to resolve horizontal shears with vertical scales between 0.10 and 2 m. A 4 MHz Z-80A microprocessor with 4 kbytes of memory, together with an arithmetic processor chip, constitute the control and data processing section of the ML probe. A 12-bit analogue-to-digital converter and multiplexer provide the ability to digitise outputs from up to 16 analogue sensors, while four 50 MHz counters allow sensors with frequency outputs to be used. Power is supplied to the probe via a 100 m cable which also contains the data communication lines operating at 38 400 bits/s. A feature of the ML probe is the integration of custom and commercial electronic circuitry and sensors to provide the best characteristics at optimum cost.     

基于液态电极差动电容的电子水平仪

设计了一种以液态电极差动电容作为倾角传感器的电子水平仪.选用新型电容数字转换器(CDC)芯片AD7746,直接将传感器的电容信号转换成数字量,通过I2C总线交由PIC16F72处理,通过LCD直观显示倾斜角度.     

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.     

Digital synchronous detector with a generator of a slowly varying signal

A synchronous detector based on a counter, memory device (RAM or ROM), and multiplicating digital-to-analog converter is described. At a ±25-V acceptable input signal, the output bias drift referred to the input is less than 30 μV, input bias suppression is 56 dB, and harmonic (the third and higher ones) suppression is no lower than 33 dB. The device can be used as a two-channel generator of arbitrarily shaped signals (from ultralow frequencies to 15 kHz).     

基于DSP的宽动态范围莫尔条纹计数与精密细分技术

为莫尔条纹的计数与细分提供了一种基于DSP(数字信号处理器)的高速软件解决方案。它能有效的解决传统系统中计数电路与细分功能不能无缝匹配的问题,提高测量的准确性。由于采用了高速信号处理和闪烁采样技术,采用该方案的系统能处理宽动态范围的莫尔条纹信号。提供的实例能对从直流到1MHz的莫尔条纹信号进行计数与细分,对于1μm光学分辨率的光栅测长系统来说,其相应的最高测量速度为1000mm/s,细分步长可以达到nm级。     

旋转机械故障窄带信号的循环平稳特征分析

阐述了窄带叠加正弦调幅信号的循环平稳特征,指出了窄带叠加正弦调幅信号与其对应的确定性正弦调幅信号循环矩相比,循环频率不变,仅将确定性幅值变成了随机幅值,幅值的大小和相位发生了变化;并以旋转机械中使用最为广泛的轴承故障的诊断为例,对机械故障的窄带信号循环平稳特征进行了分析;使用傅氏级数及相关分析理论,给出了周期冲击信号循环自相关函数数学表达式,得到了故障存在于内外环和滚动体上的二阶循环频率大小;最后通过实例分析证明了理论的正确性。     

Modular design of a long-term portable recorder for physiological signals

A portable biomedical signal recorder is valuable for the detection of acute symptoms. By the use of an ambulatory recorder, investigators and clinicians have more opportunity to analyze paroxysmal or sudden symptoms from the long-duration recorded signals. We propose a modular recorder that contains a motherboard, modules, and an isolated RS-232 interface. The modules have been modified to measure electrogastrogram (EGG), electrocardiogram (ECG), and electroencephalogram (EEG) signals. The compact motherboard includes a microcontroller with a built-in A/D converter, secure digital (SD) memory card, and the driven-right-leg (DRL) circuit. The power consumption of the proposed recorder is less than 2 mA (6 mW). It can continuously record a lead-II ECG signal with a 10-bit resolution for 3.9 days. As a result, the design is suitable for the purpose of long-term portable recording.     

A Digital Analyzer for a 3-mm-Band Radiospectrometer

The digital analyzer is a part of a multichannel modulation-type radiometric detector intended for studying radiation lines of impurity gases in the Earth's atmosphere in a frequency range of 96–110 GHz. The signal passing through one of the radiospectrometer's analog filtering channels is digitized at an intermediate frequency of 30 MHz. A digital filtering algorithm based on the quadrature conversion is described. Software implementing this algorithm was developed. The structure of the input system and the interface between the analog-to-digital converter and the control computer are described. A distinct feature of the interface is its 32-Kbyte buffer memory. The test results are presented.     

Note: a flexible light emitting diode-based broadband transient-absorption spectrometer

This Note presents a simple and flexible ns-to-ms transient absorption spectrometer based on pulsed light emitting diode (LED) technology that can be incorporated into existing ultrafast transient absorption spectrometers or operate as a stand-alone instrument with fixed-wavelength laser sources. The LED probe pulses from this instrument exhibit excellent stability (～0.5%) and are capable of producing high signal-to-noise long-time (>100 ns) transient absorption signals either in a broadband multiplexed (spanning 250 nm) or in tunable narrowband (20 ns) operation. The utility of the instrument is demonstrated by measuring the photoinduced ns-to-ms photodynamics of the red/green absorbing fourth GMP phosphodiesterase/adenylyl cyclase/FhlA domain of the NpR6012 locus of the nitrogen-fixing cyanobacterium Nostoc punctiforme.     

A Controller for the Study of Fast Processes

A controller has been developed that forms a sequence of rectangular RF pulses, performs a fast synchronous (synchronized with the pulse sequence) analog-to-digital (AD) conversion of the electric signals, writes digital data in to the RAM, and transmits these data to the ISA (IBM PC) bus. The program control of the position and duration of the formed pulses (with a step of 20 ns), as well as of the carrier frequency of RF pulses (up to 25 MHz with a step of 0.01 Hz), is ensured. The fast parameters of the AD conversion are the following: the digit capacity is eight bit and the sampling frequency is 50 MHz.     

An adaptive γ-ray spectrometer with a high event processing rate

A fast γ-ray spectrometer adaptable to the scintillator type is described. This spectrometer is capable of processing a γ-ray energy spectrum (with a resolution of <4% in the energy range from 20 keV to 10 MeV) in a sequence of time intervals in the real-time mode at a counting rate of up to 10⁶ cps. Digitization of the detector signals by a 14-bit ADC with a sampling rate of 64 MHz and real-time data stream processing are used to separate overlapping events and correctly generate energy spectra.     

一种基于多相结构的VLBI数字基带转换器设计

介绍了深空测控系统中VLBI数字基带转换器的原理及其未来发展方向,详细研究了基于多相结构滤波器组算法和频点可调带宽可变技术.本文基于VLBI2010计划的设想和未来我国深空探测任务的需要,参照国外相关设备的指标,将多相结构全频域接收并行处理的优势和数字本振+高效滤波结构的频带选取灵活的特点相结合,提出更有利于以软件无线...