High Performance Power Spectrum Analysis Using a FPGA Based Reconfigurable Computing Platform

Power-spectrum analysis is an important tool providing critical information about a signal. The range of applications includes communication-systems to DNA-sequencing. If there is interference present on a transmitted signal, it could be due to a natural cause or superimposed forcefully. In the latter case, its early detection and analysis becomes important. In such situations having a small observation window, a quick look at power-spectrum can reveal a great deal of information, including frequency and source of interference. In this paper, we present our design of a FPGA based reconfigurable platform for high performance power-spectrum analysis. This allows for the real-time data-acquisition and processing of samples of the incoming signal in a small time frame. The processing consists of computation of power, its average and peak, over a set of input values. This platform sustains simultaneous data streams on each of the four input channels.Comment: 5 pages, 3 figures. Published in the Proceedings of the IEEE International conference on Reconfigurable Computing and FPGAs (ReConFig 2006). Article also available at http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4100006&isnumber=409995

A new method of deconvolution and its application to lunar occultations

A new method of deconvolution is described which uses our prior knowledge about the solution to derive some of the information obscured in the data because of the smoothing nature of convolution and the presence of noise. It uses a regularized least-squares criterion of agreement with the data, according to which the computed solution will lead to a minimum variance of noise and also be smooth in the sense of minimum variance of its second-differences. In addition, the present optimum deconvolution method (ODM) also constrains this solution to satisfy our prior knowledge about it by using a combination of a new algorithm for incorporating bounds on the solution like positivity, and the Lagrange multiplier method for equality-constraints. The new algoritham is a rapidly converging sequence of iterations for minimizing a weighted sum of squares of the deviation of the solution from the specified bounds. For the sake of illustration, ODM is compare with the conventional method of Scheuer for deconvolving the lunar occultation data to derive the brightness distribution of a radio source. The required occultation data have been obtained both from computer stimulations and from the observations of occultation with the Ooty radio telescope. A comparison of the restorations using the two methods indicates that a) ODM can be effectively applied even in very noisy situations; b) it leads to superresolution, implying an improvement in resolution by about a factor of two over the conventional method; and c) ODM provides a "clean" output leaving all the effects of noise to the residuals. A practical procedure has also been discussed for obtaining the effective resolution and restoring errors from an analysis of the residuals, perticularly their variance and power spectrum

On the interpretation of the observed angular-size-flux-density relation for extragalactic radio sources

The interpretation of the observed relation between median angular sizes (θm) of extragalactic radio sources and flux density at 408 MHz has been examined. The predicted θm-S relations based on well-observed strong sources in parent samples selected at 178 and 1400 MHz, and existing models of the evolving radio luminosity function can be made to fit the observed relation only by invoking cosmological evolution in linear sizes even for the q0 = 0 universe. Predictions based on a parent sample at 2.7 GHz are shown to overestimate the contribution of steep-spectrum, compact (SSC) sources in low-frequency samples unless the downward curvature in the spectra of such sources is taken into account. When approximate corrections are made for this effect, predictions based on the 2.7 GHz parent sample cannot obviate the need for linear size evolution as claimed in the literature

MSH 05-22 - a giant radio source in the Southern sky

During a program of mapping a complete sample of extended radio sources with the Molonglo Observatory Synthesis Telescope (MOST), the source MSH 05-22 (0503-286) was discovered to be a giant radio source. Our map at 843 MHz clearly suggests the association of the observed radio emission, extending over 42 arcmin, with a 15.5 mag D-galaxy. The galaxy redshift of z = 0.0384 leads to a projected linear extent of 2.6 Mpc (H0 = 50 kms-1Mpc-1), making this the largest known radio source in the southern sky

The Molonglo Reference Catalog 1-Jy radio source survey IV. Optical spectroscopy of a complete quasar sample

Optical spectroscopic data are presented here for quasars from the Molonglo Quasar Sample (MQS), which forms part of a complete survey of 1-Jy radio sources from the Molonglo Reference Catalogue. The combination of low-frequency selection and complete identifications means that the MQS is relatively free from the orientation biases which affect most other quasar samples. To date, the sample includes 105 quasars and 6 BL Lac objects, 106 of which have now been confirmed spectroscopically. This paper presents a homogenous set of low-resolution optical spectra for 79 MQS quasars, the majority of which have been obtained at the Anglo-Australian Telescope. Full observational details are given and redshifts, continuum and emission-line data tabulated for all confirmed quasars.Comment: 40 pages, ApJS in pres