射频部分替代法的衰减测量分析

限制衰减测量量程的因素是大信号测量的非线性以及小信号测量的信噪比，采用射频部分替代法能够在加大信号功率提高信噪比的同时而不引入大信号测量的非线性，是扩展衰减量程的有效方法。本文论述了射频部分替代法，并对不确定度进行了分析。     

串联替代法衰减测量装置的噪声分析

在微波大衰减测量中，噪声是一项主要误差来源。本描述了低中频串联替代法衰减测量装置中噪声误差的分析方法，对中国计量科学研究院新建的宽带衰减基准中噪声引入的误差进行了理论分析和测试，并给出了分析和测试结果。     

新建立的衰减计量国家标准装置

为了满足大衰减量值的溯源，研制成功了新的PAS-1型衰减测量接收机和新的国家标准装置。文中论述了该标准装置的原理及特点，详细分析了它的不确定度。试验表明：该标准装置频带可扩展到18GHz，量程达100dB，在100dB量程的测量不确定度优于0．1dB，置信概率为95％。     

纳伏电压标准装置测量不确定度分析与评定

通过实验与经验分析,考虑零点漂移、环境温度、量程非线性、数据处理、信号衰减、信号传输、频率响应、噪声与干扰等因素的影响,对纳伏电压标准装置进行了测量不确定度分析与评定。给出了实验数据和评定结果,提出了提高纳伏级微弱信号测量准确度的建议。     

谐振梁在高量程加速度传感器非线性测试中的应用

介绍了一种高量程加速度传感器非线性的新测量方法。用谐振梁与振动台系统组成新的谐振系统．这一系统对振动台的振动信号具有放大作用,从而解决了用小量程振动台标定大量程加速度传感器非线性的难题。详述了用谐振梁法测量高量程加速度传感器非线性的实际操作过程,总结了试验过程中的方法和经验,对高量程加速度传感器非线性测量具有实际指导作用。     

利用 T矩阵法实现大衰减量的测量

针对现有衰减校准系统量程小,难以满足步进衰减器等大衰减量计量需求的问题,通过对微波网络理论的分析研究,提出了利用T矩阵法实现大衰减量测量的方案,介绍了微波网络参数的模型,详细介绍了T矩阵法的实现过程,经过实测验证,方案可行,可为大衰减量的计量测试提供一套切实可行的解决方案。     

双通道衰减测量系统的串扰分析

通过对双平衡混频器的分析,推导出双通道衰减测量系统串扰的分析模型,并对双通道衰减测量系统进行了泄漏测试,验证了分析结果。基于分析结果,得出本振通道的隔离度应不小于120 dB的设计,以使在100 dB量程,串扰影响不大于0.01 dB。串扰分析模型对毫米波双通道衰减测量系统的设计以及不确定度评定具有一定的参考价值。     

浅谈低频替代法在毫米波段衰减校准装置中的应用

通过分析传统衰减校准方法的优点,以感应分压器作为衰减校准的主标准器,采用串联低频替代法组成毫米波衰减校准装置,满足迅速发展的毫米波技术对衰减参数计量检定的要求。     

利用低频替代法实现在毫米波段衰减参数的自动测试

本文介绍通过结合多种传统衰减测试方法的优点 ,以感应分压器作为衰减测试的标准 ,采用串联低频替代法组成毫米波衰减自动测试系统 ,满足迅速发展的毫米波技术对衰减参数检定的要求。     

漫谈信号线

音响系统中,音源至前级放大器再到功率放大器之间的连接就是用信号线,它的任务是输送音频模拟信号。与解码器连接的线材称数字线。对信号线的要求是,不失真的输送信号,尽量减小阻力,减小信号衰减,不仅频域要宽,高、中、低频能量也应均衡,屏蔽外来的RF（射频干扰）和EMI（电磁干扰）的性能好。音乐背景宁静、信噪比高,中胜,即信号的传输原汗原味,声音无染色。     

Position sensing for high track density recording

Progress towardhigher digital areal densities is related to the data track position sensing accuracy obtainable in future disk drives. In most systems available, position sensing is done remotely from the data track and subject to different dimensional stability conditions. To obtain higher track densities, position sensing reference information must be moved near the data track. Several techniques are available to embed reference information in the data track. All the techniques described have one of two basic principles of operation. One method uses comparison of reference signal amplitudes and the second method uses arrival time differences of reference signals. The time method is relatively unknown but offers the designer some new alternatives. This paper describes an overview of several methods. Relationships are derived to relate the influence of noise on both basic methods. Linearity, relative hardware simplicity, and track capture range are also discussed. It is our conclusion that the Amplitude or Tri-Bit method offers the greatest hardware simplicity, but is limited by noise and non-linearity at high track densities. The time dependent or Chevron method requires two data channels, but offers a relatively higher noise immunity, better linearity, and higher data capacity.     

基于噪声水平自适应估计的往复压缩机振动信号局部投影降噪方法

局部投影降噪算法在其应用过程中,邻域的选择对降噪效果有较大影响。提出了改进算法以解决传统算法中邻域难以选取的问题。该方法利用小波包分解技术,依据频带能量的差异将原始信号分解为噪声频带和系统信号频带,将噪声频带能量占原始信号能量的比值估计为噪声水平。在一定程度内逐步增加分解层数,直至该噪声水平收敛。根据收敛时的噪声水平估计相空间中相点的邻域半径,此外利用该噪声水平可实现对原始信号的盲信噪比估计。对含噪的Lorenz和Rossler序列进行数值仿真,结果表明该方法的降噪效果优于一些传统方法和基于定量递归分析的局部投影降噪算法。对实测往复压缩机振动信号的降噪研究,进一步表明了该方法的有效性。     

Recognition of unsegmented targets invariant under transformations of intensity

Images taken in noncooperative environments do not always have targets under the same illumination conditions. There is a need for methods to detect targets independently of the illumination. We propose a technique that yields correlation peaks that are invariant under a linear intensity transformation of object intensity. The new locally adaptive contrast-invariant filter accomplishes this by combining three correlations in a nonlinear way. This method is not only intensity invariant but also has good discrimination and resistance to noise. We present simulation results for various intensity transformations with and without random and correlated noise. When the noise is high enough to threaten errors, the method trades off intensity invariance in order to achieve the optimum signal to noise ratio, and the peak to sidelobe ratio in the presence of clutter is always greater than one. In the presence of random disjoint noise, the signal to noise ratio is independent of the target contrast and of the level of the noise.     

自适应分解层数的小波域中值滤波振动信号降噪法

为降低结构健康监测加速度信号中常见的白噪声以及脉冲噪声,提出了中值滤波与小波阈值降噪相结合的方法。分解层数对降噪效果有着重要影响,为取得更好的降噪效果,提出了一种分解层数自适应确定法,并给出了各层阈值的取值方法。数值模拟以及国家游泳中心健康监测系统实测数据分析结果表明,所提出的方法克服了传统阈值降噪法对脉冲噪声拟制效果不理想的缺陷,能同时有效降低白噪声以及脉冲噪声,为模态参数识别等提供更高信噪比的分析数据。     

110 kV变电站噪声污染分析及控制

为掌握110 kV城市变电站的噪声污染水平,对正常运行的某110 kV变电站的主变及站界噪声进行系统测量,并对测试结果进行计算和分析。结果显示110 kV变电站的噪声频谱峰值主要集中在100 Hz～2 000 Hz的范围内,噪声以电磁噪声和冷却系统风机噪声为主;站界噪声测试结果显示大部分测点的昼夜噪声值均严重超标。对变电站噪声的污染特性、频谱特性和衰减规律进行分析研究,借助噪声衰减的理论,提出使变电站站界噪声达标的主要方法,为变电站设计和噪声控制提供参考。     

Discrete-time method for signal-to-noise power ratio measurement

The measurement of signal-to-noise power ratio (SNR) is of fundamental importance in many areas of electrical engineering, such as communications, signal processing, tests and measurements, circuits and systems, etc. In this paper, we propose two algorithms for estimating the signal-to-noise ratio of a noisy sinewave from discrete-time data obtained by sampling the input signal. One algorithm is based on the estimation of the four parameters of the input sinewave. The second algorithm is based on estimating the average noise power by averaging the squared magnitude of the FFT bins attributed to the noise. Both methods show excellent performance. Simulation results indicate that the four-parameter method requires the input SNR to be at least 10 dB and the input signal frequency not exceeding one-third of the sampling frequency. On the other hand, the second approach, the spectrum averaging method, shows a remarkable robustness over a very wide range of normalized frequencies (with respect to the Nyquist frequency) and SNRs (well over 100 dB). This spectrum averaging method should prove to be very useful in a wide range of applications     

基于奇异值分解的信号特征提取方法研究

奇异值反映了信号中有用信号和噪声的能量分布情况,通过奇异值分解可以将隐含在噪声中的特征信号提取出来。本文提出了在强背景噪声中基于奇异值分解的特征提取方法。研究发现,随着信号信噪比的降低,奇异值的分布趋于直线,特征信号难以分离和提取。通过增加奇异值分解阶次,可以使反映噪声能量的奇异值的分布范围扩大,使得噪声的能量相对分散,凸显出了反映有用信号能量的奇异值,从而有利于特征信号的提取。仿真试验和故障分析实例都验证了该方法的可行性。     

基于MUSIC功率谱估计的直升机空中信号分析

针对直升机飞行的辐射噪声特征谱线进行分析,提出一种基于MUSIC算法的直升机声信号处理方法。首先阐述MUSIC谱估计方法,然后针对实测不同机型直升机的飞行辐射噪声数据,分别进行MUSIC算法和传统方法的频谱分析,对得到的结果进行分析比较,数据处理结果表明MUSIC算法能够抑制噪声,明显改善信噪比,并能够更为细致地体现直升机声信号的谐波特性。     

Analytical differentiation of the differential-absorption-lidar data distorted by noise

A method of analytical differentiation is developed for processing differential absorption lidar (DIAL) data. The method is based on simple analytical transformation of the DIAL on and off signal ratio. The derivatives consequently are found for either individual data points or local zones of the measurement range. The method makes possible the separation of local zones of interest and the separate investigation of these. The smoothing level is established by the selected value of the exponent in a transformation formula rather than by the selection of the resolution range. The method does not require the calculation of local signal increments. This reduces significantly the high-frequency noise in the measured concentration. The method is general and can be used for different experimental data, including inelastic (Raman) lidar data. The processing technique is practical and does not require a determination of the solution for a large set of algebraic equations. It is based on the simple repetition of the same type of calculations with different constants. The method can easily be implemented for practical computations.