共查询到17条相似文献，搜索用时 109 毫秒
1.
2.
3.
4.
纪志浩 《中国科学院上海天文台年刊》1989,(10):183-188
在射电干涉仪中，单边带系统和双边带系统都有广泛的作用。本主要讨论了单、双边带系统中相关器输出中的条纹相位与本振相位、延迟、仪器相位的关系。特别对多资频率变换系统的相位关系作了论述。并指出了它们的优缺点。 相似文献
5.
6.
7.
针对同波束干涉测量中差分相位时延模型验证、解算结果周跳检测与校正问题进行分析。给出了相位闭合和差分相位时延闭合计算原理与方法,并以SELENE任务中解算的差分相位时延数据为算例进行分析,差分相位时延闭合计算结果小于几皮秒。验证了差分相位时延基于同一波前的模型,可用于对差分相位时延中周跳问题进行检测,可对数据波动情况进行监视,为数据后处理提供依据。在实际应用中,该方法可随着数据处理过程的推进同步进行,因此,十分有利于同波束干涉测量方法的实时实施,并应用于卫星导航。 相似文献
8.
9.
10.
11.
12.
13.
14.
This paper describes the design, tests and preliminary results of a real-time parallel signal processor built to aid a wide
variety of pulsar observations. The signal processor reduces the distortions caused by the effects of dispersion, Faraday
rotation, doppler acceleration and parallactic angle variations, at a sustained data rate of 32 Msamples/sec. It also folds
the pulses coherently over the period and integrates adjacent samples in time and frequency to enhance the signal-to-noise
ratio. The resulting data are recorded for further off-line analysis of the characteristics of pulsars and the intervening
medium. The signal processing for analysis of pulsar signals is quite complex, imposing the need for a high computational
throughput, typically of the order of a Giga operations per second (GOPS). Conventionally, the high computational demand restricts
the flexibility to handle only a few types of pulsar observations. This instrument is designed to handle a wide variety of
Pulsar observations with the Giant Metre Wave Radio Telescope (GMRT), and is flexible enough to be used in many other high-speed,
signal processing applications. The technology used includes field-programmable-gate-array(FPGA) based data/code routing interfaces,
PC-AT based control, diagnostics and data acquisition, digital signal processor (DSP) chip based parallel processing nodes
and C language based control software and DSP-assembly programs for signal processing. The architecture and the software implementation
of the parallel processor are fine-tuned to realize about 60 MOPS per DSP node and a multiple-instruction-multiple-data (MIMD)
capability. 相似文献
15.
16.
Saurabh Singh Ravi Subrahmanyan N. Udaya Shankar Mayuri Sathyanarayana Rao B. S. Girish A. Raghunathan R. Somashekar K. S. Srivani 《Experimental Astronomy》2018,45(2):269-314
The global 21-cm signal from Cosmic Dawn (CD) and the Epoch of Reionization (EoR), at redshifts \(z \sim 6-30\), probes the nature of first sources of radiation as well as physics of the Inter-Galactic Medium (IGM). Given that the signal is predicted to be extremely weak, of wide fractional bandwidth, and lies in a frequency range that is dominated by Galactic and Extragalactic foregrounds as well as Radio Frequency Interference, detection of the signal is a daunting task. Critical to the experiment is the manner in which the sky signal is represented through the instrument. It is of utmost importance to design a system whose spectral bandpass and additive spurious signals can be well calibrated and any calibration residual does not mimic the signal. Shaped Antenna measurement of the background RAdio Spectrum (SARAS) is an ongoing experiment that aims to detect the global 21-cm signal. Here we present the design philosophy of the SARAS 2 system and discuss its performance and limitations based on laboratory and field measurements. Laboratory tests with the antenna replaced with a variety of terminations, including a network model for the antenna impedance, show that the gain calibration and modeling of internal additive signals leave no residuals with Fourier amplitudes exceeding 2 mK, or residual Gaussians of 25 MHz width with amplitudes exceeding 2 mK. Thus, even accounting for reflection and radiation efficiency losses in the antenna, the SARAS 2 system is capable of detection of complex 21-cm profiles at the level predicted by currently favoured models for thermal baryon evolution. 相似文献