Transmission Characteristics of an FM Signal Through a Hard Limiting Repeater

The response of an FM detector to an FM signal which is passed through a hard limiting repeater together with additive Gaussian noise is described. A general expression of the output SNR is derived that enables the determination of the threshold behavior. To clarify the feature of a transmission characteristic, a comparison with a linear repeater is also made. The output SNR is found to be larger than that of the linear system for all practical values of input CNR's.     

无束缚系统效应时人体弹射过载耐力的测定

本工作采用电子振荡线路模型对人体弹射过载耐力进行研究。人体是弹性体,他受到弹射力作用后的运动规律与电子振荡线路的电流运动相似,都可用相同的微分方程表达,只要它们的固有频率和阻尼比相同,电子模型即可代替人体进行实验。电子模型主要参数为带宽0～100多Hz,主固有频率10.5Hz,阻尼比0.3。将模拟的弹射信号输入到模型中去,即可得输出信号,它的波幅即代表作用在人体上的过载值,然后根据人体脊椎骨耐压强度,即可获得输入波形与耐力之间的关系。通过一系列实验,求得输入不同波形时人体的耐力数据和耐力曲线。     

Wave resistance of rough plane channel walls in the supersonic flow

We propose a method that makes it possible to obtain in the framework of linear approximation the exact formulas for the wave resistance of the channel walls with an arbitrary plane pattern in the first and subsequent interference zones. It is shown by a particular example of the sinusoidal pattern that the pressure wave interference may lead to the positive or negative resistance resonance.     

一种有效的消波装置

对无限长渠道中小振幅入射波通过两块间距为ｌ,透水性能不同的多孔透水板的反射和透射进行了研究。应用分离变量法得到了反射波和透射波的波形。结果表明,当ｌ为入射波半波长的倍数时,反射波和透射波振幅最大,消波效果差,最佳消波率为５０％。当ｌ为入射波１／４波长加半波长的倍数时,反射波和透射波振幅最小,消波效果好,最佳消波率大于５０％。此外,还得到了无反射波的条件。     

基于Laguerre函数的高压力非线性传感器补偿研究

针对高压力传感器线性化输出的结果不准确的现象,研究了具有针对性的Duffing非线性系统。用传感器的输出数据作为补偿器的输入,传感器的输入数据作为补偿器的输出,进行基于Laguerre函数的非线性动态补偿器的设计研究。该方法无需知道传感器的非线性阶数,对于外界干扰有较强的抑制作用,对于时延对象也具有一定的优势。利用该补偿器对传感器进行动态补偿,将补偿结果与阶跃响应输出进行对比,结果表明该非线性模型补偿的有效性。     

Output of a Balanced Frequency Discriminator Driven by a Sine Wave and Gaussian Noise

The output of a realizable balanced frequency discriminator is calculated for an input consisting of a sine wave plus Gaussian noise. Explicit autocorrelation and power spectra are found for one practical embodiment of the discriminator for various input carrier-to-noise ratios, with the carrier tuned to center frequency and also off-center. The formulas also permit the calculation of the output for the case of a spectrum of noise slowly swept through the discriminator. Although qualitatively similar to results previously obtained with an ideal discriminator, substantial differences are also found. Measurements are made that closely verified the theoretical results. No limiting is assumed.     

EMD滤波在捷联惯导晃动基座初始对准中的应用

为了实现晃动基座情况下光纤捷联惯性导航系统的高精度初始对准,提出了一种基于经验模态分解(EMD)法去噪的抗干扰初始对准算法。该算法在凝固惯性系下进行姿态更新,以反映载体在晃动干扰下的姿态变化,从而消除角运动干扰的影响;并针对EMD法的不足对其进行改进,然后对加速度计的输出进行去噪,以消除线运动干扰的影响。结果表明:改进后的EMD法具有良好的去噪效果,基于EMD法去噪的抗干扰初始对准算法具有角运动和线运动的干扰抑制能力,能够实现晃动基座下的高精度抗干扰初始对准。     

Mean Power Estimation with a Recursive Filter

Power estimates from smoothed detector outputs of stationary signals are analyzed for linear, square law, and logarithmic receiverdetectors. Smoothing is accomplished with a first-order recursive digital filter. lnput amplitude is assumed to be Rayleigh distributed and detector output samples independent. Expansion of results to other distributions is indicated.     

斩控式机场助航灯光恒流调光源的研制

提出了一种PWM斩控式机场助航灯恒流调光源设计方案。应用PWM控制的AC／AC降压变换器,对负载电压进行调节,从而获得高质量和稳定的正弦负载电流。1kVA样机实验结果表明,采用该方案所设计的恒流调光源在输入电压波动和负载变化时均可以实现稳定的正弦负载电流,能够满足民用机场行业标准中对助航灯恒流调光电源的技术要求。     

Fast converging adaptive processor or a structured covariance matrix

The use of adaptive linear techniques to solve signal processing problems is needed particularly when the interference environment external to the signal processor (such as for a radar or communication system) is not known a priori. Due to this lack of knowledge of an external environment, adaptive techniques require a certain amount of data to cancel the external interference. The number of statistically independent samples per input sensor required so that the performance of the adaptive processor is close (nominally within 3 dB) to the optimum is called the convergence measure of effectiveness (MOE) of the processor. The minimization of the convergence MOE is important since in many environments the external interference changes rapidly with time. Although there are heuristic techniques in the literature that provide fast convergence for particular problems, there is currently not a general solution for arbitrary interference that is derived via classical theory. A maximum likelihood (ML) solution (under the assumption that the input interference is Gaussian) is derived here for a structured covariance matrix that has the form of the identity matrix plus an unknown positive semi-definite Hermitian (PSDH) matrix. This covariance matrix form is often valid in realistic interference scenarios for radar and communication systems. Using this ML estimate, simulation results are given that show that the convergence is much faster than the often-used sample matrix inversion method. In addition, the ML solution for a structured covariance matrix that has the aforementioned form where the scale factor on the identity matrix is arbitrarily lower-bounded, is derived. Finally, an efficient implementation is presented.     

A PDF multitarget tracker

A probability density function (pdf) based approach to the multitarget tracking problem is presented. The input data are obtained by measurements over time from a front-end detector. The desired output is the number of targets present and the parameters of each target. The same approach has previously been used for time delay detection and tracking problems and is adapted to this problem This approach is an alternative to the traditional approach of “association” and “tracking” on the measurements     

A Closely Regulated TWT Converter

The design concept for the traveling wave tube amplifier converter for possible use in the Thermoelectric Outer Planet Spacecraft (TOPS) is presented. An unusual combination of semiconductors and magnetics were utilized to achieve very stable voltage regulation on a number of separate outputs to satisfy the requirements of a high-power traveling wave tube (TWT), and at the same time operate at an efficiency of better than 90 percent from a 30-volt source. The circuitry consists of an output filter, an auxiliary Jensen oscillator driving a high-reactance transformer to provide current limiting to the heater, a variable time delay, a main Jensen oscillator driving the power transformer with a maximum step-up ratio of 120 to 1, and series transistorized post regulators to provide precise voltage adjustment and low output impedance. This paper discusses the design of the high-reactance transformer and the high step-up ratio transformer, as well as the high-voltage series regulators that are limited in range and operate at the top of the unregulated output voltage. Test data is presented, and details of current transients caused by charging the filter circuits, input current ripple, and output voltage ripples are considered. The circuit provides better than 0.5 percent regulation against load change, input voltage change, and over-operating temperature range of from -20 to + 80°C, with output ripple voltage of less than 2 volts peak-to-peak on top of the 3600-Vdc output. The measured efficiency was typically 87 percent. and recommendations are included to improve this to in excess of 90 percent.     

Spatial adaptive subspace detection in OTH radar

The work presented here addresses the problem of target detection against spatially structured interference composed of jamming plus noise, where for practical reasons, the received target wavefront may also deviate from the traditional plane wave model. This detection problem arises in over-the-horizon (OTH) radar systems where spatially distributed targets often compete for detection against directional interference that is spread over the entire range-Doppler search space. Conventional detection processing schemes are compared with a recently proposed adaptive subspace detector (ASD) that takes both the spatial structure of the interference and the possibility of target wavefront distortions into account. Experimental array data recorded by the Jindalee sky-wave and Iluka surface-wave OTH radar systems, located in central and northern Australia respectively, is used to evaluate detection performance.     

Phase Analysis in Multiple-Sensor Receivers with High Signal-to-Noise Ratio

The ideal phase detector characteristic is analyzed for estimating the phase difference between two stochastic input signals. This can essentially be described as a correlation process formed by multiplying the two input signals and extracting the phase. High signal-to-noise ratio conditions are assumed to linearize the system with respect to the noise. The effects of the nonlinearity on the signal are handled in terms of a series expansion and by using low-pass filtering on the receiver output. The mean square error of the system is calculated for some typical parameters.     

Signal-to-Noise Ratio of Arbitrary Power-Series Nonlinear Amplifier

A general analysis of the effect of an arbitrary power-series nonlinear amplifier followed by a coherent mixing device on signal-to-noise ratio (SNR) is performed. An expression is derived for the improvement factor which is defined as the logarithm of the ratio of the output SNR to the input SNR. This expression is applicable to the coherent amplitude detector and phase locked loop as well as noncoherent amplifier by appropriate selections of the detection angle. Moreover, the improvement factor can be obtained for noise with an arbitrary amplitude distribution. To demonstrate the applicability of this analysis, the improvement factors of the nonlinear amplifiers such as a power-law amplifier and a power-series amplifier with positive and negative discriminations are numerically calculated for the cases where the input noise amplitude distributions are Rician and triangular.     

Sonar Array Detection of Gaussian Signals in Gaussian Noise of Unknown Power

A statistical test is postulated for detecting, with an M-element hydrophone array, a Gaussian signal in spatially independent Gaussian noise of unknown power. The test is an extension of the uniformly-most-powerful (UMP) unbiased test for a two-element array. The output signal-to-noise ratio of the test is calculated and, for a large number of independent space-time samples, is shown to be no better than a mean-level detector (MLD). Receiver operating characteristic curves (ROC) for the MLD are computed and compared to the ROC curves for the optimum (Bayes) parametric detector. The input signal-to-noise power ratios required to provide a detection probability of 0.5 differ by less than 0.2 dB for a fifty-element array with wide variation in false-alarm probability and time-bandwidth product. This result suggests that both the extended bivariate UMP unbiased test and the MLD perform close to the unknown UMP unbiased test for independence of a multivariate Gaussian distribution.     

Variance Analysis of the Angle Output Voltage for an Amplitude Monopulse Receiver

The amplitude-comparison monopulse receiver utilizes two overlapping antenna patterns to determine the angle of arrival of an incoming RF signal for use in a direction-finding application. The thermal noise introduced by the receiver distorts the signal, causing an error in determining the exact angle of arrival of the signal. The analysis derives an expression for the deviation of the angle output voltage, or the angular error, due to receiver noise as a function of 1) the angle of arrival and 2) the signal-to-noise ratios of the two channels of the receiver. A receiver using a square-law detector and one using a linear detector are analyzed.     

Phase-Locked Loop Behavior near Threshold

The phase-locked loop behavior is analyzed following the quasilinearization Booton's method. When the loop is locked on an unmodulated input signal with a static phase error, the phase detector nonlinearity produces an interaction between the static phase error and the voltage-controlled-oscillator (VCO) noise phase fluctuations. Formulas allowing one to compute the static phase error increase and the VCO phase variance increase are derived. When the input signal is phase modulated, there is an interaction between the static phase error, the VCO noise phase fluctuations, and the input signal phase modulation. Formulas are obtained that allow one to compute the loop loss of performances (static phase error increase and VCO phase variance increase) and the coherent phase demodulator output signal-to-noise ratio decrease. Finally, a slight modification to Booton's procedure is proposed, leading to results in better agreement with experimental data.     

总体最小二乘法在NGMIMU静态解耦中的应用

无陀螺惯导系统的线性耦合是一种严重影响测量精度的系统误差。根据无陀螺惯导系统的耦合特性和总体最小二乘法 (TLS)的性质提出了一种全新的线性解耦算法 ,该算法在解算耦合系数时同时考虑了加速度计的输出误差和标定信号的输入误差 ,得到耦合系数的TLS解对输入值和输出值同时具有范数最小 ,然后用求得的耦合系数对加速度计输出进行重构 ,从而实现解耦。仿真结果表明经该算法解耦后的角速度测量值解耦误差率在 8%以下 ,解耦效果较好 ,验证了该算法的有效性。