数字化码同步器 DBS530 性能分析

介绍美国洛克希德马丁（ＬＯＣＫＨＥＥＤＭＡＲＴＩＮ）公司生产的数字化码同步器ＤＢＳ５３０的工作原理及电路组成，对其输入自动增益控制、直流基线恢复、相位误差提取及码元判决、环路滤波、频率合成等电路进行了较为详尽的分析，最后给出样机的误码性能测试数据。结果表明，ＤＢＳ５３０的实现方法是值得借鉴的，它为国内高码率数字化码同步器的研制又提供了一条可供选择的新途径。     

Coordinated optical and Yohkoh observations of 26 June 1992 flare loops

Optical spectra of large flare loops were detected by the Ondejov Multichannel Flare Spectrograph (MFS) during coordinated observations with MSDP at Pic du Midi (H) and the soft X-ray telescope (SXT) on Yohkoh. The CCD video images taken by the MFS slit-jaw camera document the time-development of the flare loops as seen through the H filter. Preliminary analysis of the MSDP images shows the intensity structure of the cool flare loops and their velocity fields. From the spectra we can clearly see the intensity variations along the cool loops. SXT images show the structure of hot X-ray loops similar to that of cool loops. Special attention is devoted to the bright tops, simultaneously observed in X-rays, H and other optical lines. Based on a preliminary analysis of the optical spectra, we speculate about possible mechanisms leading to an observed bright emission at the tops of cool loops. We suggest that direct soft X-ray irradiation of cool loops at their tops could be, at least partly, responsible for such a strong brightening.     

A high dynamics algorithm based on steepest ascent method for GNSS receiver

High dynamic conditions impose critical challenges on Global Navigation Satellite System (GNSS) receivers, leading to large tracking errors or even loss of tracking. Current methods that intend to improve receivers’ adaptability for high dynamics require either complicated structures or prior statistical information of noises. This paper proposes a high dynamics algorithm based on steepest ascent method that can circumvent the deficiencies of existing methods. First, the relationship between the error of carrier tracking and the maximum of Fast Fourier Transform (FFT) outputs is established, and a performance function based on the steepest ascent method is designed. It can keep stable in high dynamics. Second, a new carrier-tracking loop is constructed by deploying the performance function. When the variation of GPS receiver acceleration ranges from 10 g to 100 g, compared with the PLL that either loses lock or keeps tracking accuracy less than 33.89 Hz, the experimental results show that the proposed method can not only keep tracking, but also achieve tracking accuracy more than 2.77 Hz.     

Microwave Diagnostics of Dynamic Processes and Oscillations in Groups of Solar Coronal Magnetic Loops

Low-frequency (LF) modulations of the solar microwave radiation (37 GHz) recorded at the Metsähovi Radio Observatory, are analyzed. Since the intensity of solar microwave radiation, produced by the electron gyrosynchrotron mechanism, is dependent on a value of the background magnetic field [Dulk, G. A.: 1985, Ann. Rev. Astron. Astrophys. 23, 169–224], slow variations of the magnetic field associated with disturbances of the electric current in a radiating source, can modulate the intensity of the microwave radiation. The observed multi-track features of the LF spectra are interpreted as a signature of a complex multi-loop structure of the radiating source. Application of the equivalent electric circuit models of interacting loops allows to explain and reproduce the main dynamical features of the observed LF modulation dynamic spectra.     

Experimental investigation of shock-buffet criteria on a pitching airfoil

An experimental investigation of the shock-buffet phenomenon subject to unsteady pitching supercritical airfoil around its quarter chord has been conducted in a transonic wind tunnel. The model was equipped with pressure taps connected to the fast response pressuretransducers. Measurements were conducted at different free-stream Mach number from 0.61 to0.76. The principle goal of this investigation was to experimentally discuss the shock-buffet criterion over a SC(2)-0410 supercritical pitching ...