Gigabit Digital Filter Bank: Digital Backend Subsystem in the VERA Data-Acquisition System
25 Feb 2005-Publications of the Astronomical Society of Japan (Oxford University Press)-Vol. 57, Iss: 1, pp 259-271
TL;DR: The Gigabit Digital Filter Bank (GDFB) as discussed by the authors was developed for the VERA project, which is a project to construct a new Japanese VLBI array dedicated to make a 3D map of our Milky Way Galaxy in terms of high precision astrometry.
Abstract: The VERA terminal is a new data-acquisition system developed for the VERA project, which is a project to construct a new Japanese VLBI array dedicated to make a 3-D map of our Milky Way Galaxy in terms of highprecision astrometry. New technology, a gigabit digital filter, was introduced in the development. The importance and advantages of a digital filter for radio astronomy have been studied as follows: (1) the digital filter can realize a variety of observation modes and maintain compatibility with different data-acquisition systems (Kiuchi et al. 1997 and Iguchi et al. 2000a), (2) the folding noise occurring in the sampling process can be reduced by combination with a higher-order sampling technique (Iguchi, Kawaguchi 2002), (3) and an ideal sharp cut-off bandedge and a flat amplitude/phase responses are approached by using a large number of taps available to use LSI of a large number of logic cells (Iguchi et al. 2000a). We developed the custom Finite Impulse Response filter chips and manufactured the Gigabit Digital Filter Banks (GDFBs) as a digital backend subsystem in the VERA terminal. In this paper, the design and development of the GDFB are presented in detail, and the performances and demonstrations of the developed GDFB are shown.
Citations
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TL;DR: In this paper, the authors developed the smoothed bandpass calibration (SBC) method and the best suitable scan pattern to optimize radio spectroscopic observations, which is applied to the spectrum toward OFF-source blank sky adjacent to a target source direction for the purpose of bandpass correction.
Abstract: We have developed the Smoothed Bandpass Calibration (SBC) method and the best suitable scan pattern to optimize radio spectroscopic observations. Adequate spectral smoothing is applied to the spectrum toward OFF-source blank sky adjacent to a target source direction for the purpose of bandpass correction. Because the smoothing process reduces noise, the integration time for OFF-source scans can be reduced keeping the signal-to-noise ratio. Since the smoothing is not applied to ONsource scans, the spectral resolution for line features is kept. An optimal smoothing window is determined by bandpass flatness evaluated by Spectral Allan Variance (SAV). An efficient scan pattern is designed to the OFF-source scans within the bandpass stability timescale estimated by Time-based Allan Variance (TAV). We have tested the SBC using the digital spectrometer, VESPA, on the VERA Iriki station. For the targeted noise level of 5× 10 as a ratio to the system noise, the optimal smoothing window was 32 – 60 channels (ch) in the whole bandwidth of 1024 ch, and the optimal scan pattern was designed as a sequence of 70-s ON + 10-s OFF scan pairs. The noise level with the SBC was reduced by a factor of 1.74 compared with the conventional method. The total telescope time to achieve the goal with the SBC was 400 s, which was 1 3 of 1200 s required by the conventional way. Improvement in telescope time efficiency with the SBC was calculated as 3×, 2× and 1.3× for single-beam, dual-beam, and on-the-fly (OTF) scans, respectively. The SBC works to optimize scan patterns for observations from now, and also works to improve signal-to-noise ratios of archival data if ONand OFF-source spectra are individually recorded, though the efficiency depends on the spectral stability of the receiving system.
23 citations
TL;DR: In this paper, the authors derived the correlated flux densities of 877 detected sources in three ranges of projected baseline lengths and determined the suitability of given sources as phase calibrators for dual-beam and phase-referencing observations at high frequencies.
Abstract: We observed at 22 GHz with the VLBI array VERA a sample of 1536 sources with correlated flux densities brighter than 200 mJy at 8 GHz. One half of target sources has been detected. The detection limit was around 200 mJy. We derived the correlated flux densities of 877 detected sources in three ranges of projected baseline lengths. The objective of these observations was to determine the suitability of given sources as phase calibrators for dual-beam and phase-referencing observations at high frequencies. Preliminary results indicate that the number of compact extragalactic sources at 22 GHz brighter than a given correlated flux density level is twice less than at 8 GHz.
23 citations
Cites methods from "Gigabit Digital Filter Bank: Digita..."
...The left circular polarization in the 21.97–22.47 GHz band was received, sampled with 2 bit quantization, and filtered using the VERA digital filter (Iguchi et al. 2005) before being recorded onto magnetic tapes....
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21 citations
TL;DR: In this paper, the authors reported the results of multi-epoch observations of Sgr A* with VLBI Exploration of Radio Astrometry (VERA) at 43 GHz, carried out from 2004 to 2008.
Abstract: We report the results of multi-epoch observations of Sgr A* with VLBI Exploration of Radio Astrometry (VERA) at 43 GHz, carried out from 2004 to 2008 We detected a time variation of flux at 11 % level and intrinsic size at 19 % In addition, comparisons with previous Very Long Baseline Array (VLBA) results shows that Sgr A* underwent the flaring event at least longer than 10 days in May 2007 The intrinsic size of Sgr A* remained unchanged within 1 $\sigma$ level from the size before/after the flaring event, indicating that the brightness temperature of Sgr A* was increased The flaring event occurred within 31 d, which is shorter than the refractive time scale Moreover it is difficult to explain the increase in the spectral index at the flaring event by the simple interstellar scattering model Hence, the flaring event is most likely associated with the changes in intrinsic properties of Sgr A* We considered the origin of the brightness temperature variation, and concluded that the flaring event of Sgr A* could be explained by the continuous heating of electrons, such as a standing shock in accretion flow
21 citations
Cites methods from "Gigabit Digital Filter Bank: Digita..."
...Left-hand circular polarization (LHCP) signals were received and sampled with 2-bit quantization, and filtered using the VERA digital filter unit (Iguchi et al. 2005)....
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References
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Book•
01 Jan 1986
TL;DR: In this paper, a theory of interferometry and synthesis imaging analysis of the Interferometer Response Geometric Relationships and Polarimetry Antennas and Arrays Response of the receiving system Design of the Analog Receiving System Digital Signal Processing Very-Long-Baseline Interferometry Calibration and Fourier Transformation of Visibility Data Deconvolution, Adaptive Calibrration, and Applications Interferometers Techniques for Astrometry and Geodesy Propagation Effects Van Cittert-Zernike Theorem, Spatial Coherence, and
Abstract: Preface to the Second Edition Preface to the First Edition Introduction and Historical Review Introductory Theory of Interferometry and Synthesis Imaging Analysis of the Interferometer Response Geometric Relationships and Polarimetry Antennas and Arrays Response of the Receiving System Design of the Analog Receiving System Digital Signal Processing Very-Long-Baseline Interferometry Calibration and Fourier Transformation of Visibility Data Deconvolution, Adaptive Calibration, and Applications Interferometer Techniques for Astrometry and Geodesy Propagation Effects Van Cittert-Zernike Theorem, Spatial Coherence, and Scattering Radio Interference Related Techniques Principal Symbols Author Index Subject Index
2,025 citations
TL;DR: Using the very-long-baseline interferometer, it is found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 ± 0.03 years, which provides a direct detection of a supermassive black hole binary.
Abstract: Supermassive black hole binaries may exist in the centers of active galactic nuclei such as quasars and radio galaxies, and mergers between galaxies may result in the formation of supermassive binaries during the course of galactic evolution. Using the very-long-baseline interferometer, we imaged the radio galaxy 3C 66B at radio frequencies and found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 ± 0.03 years, which provides a direct detection of a supermassive black hole binary.
147 citations
Additional excerpts
...This IF configuration is available and effective in the high-precision astrometric observation toward investigating the motion and position of radio sources; e.g. the detection of the Kepler orbital motion of some emission component close to black holes (Sudou et al. 2003)....
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TL;DR: In this paper, a commercial digital oscilloscope is used as a digitizer for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45m telescope.
Abstract: New digital spectrometers for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45-m telescope are described. A commercial digital oscilloscope is used as a digitizer. The digitizer samples analogue data with 2 bits (4 levels). Data of 512 MHz bandwidth are processed for four beams at the same time. The data-formatting unit demultiplexes 2 bits 8 data in parallel to 32 parallels and sends outputs to LSIs. General purpose LSIs for autocorrelation read the digital data with a clock rate of 32 MHz. Thirty-two LSIs of 32 lags connected in cascades calculate 1024-lag autocorrelation, and output a 1024-channel power spectrum of 512 MHz bandwidth. The bandwidth of 32 MHz is achieved by picking up the data in a rate of 1/16 in the front part of the autocorrelator module. The total performances have been demonstrated by long-term integration of noise signals from receivers and observations of the Galactic star-forming region W51 in CO line.
118 citations
TL;DR: In this article, the SIS 25-BEam Array Receiver System (BEARS) is described, which is a large focal plane array receiver system for the NRO 45 m telescope.
Abstract: A large focal plane array receiver system for the NRO 45 m telescope (SIS 25-BEam Array Receiver System, or BEARS) is described. This new array receiver uses SIS junctions and has 25 elements. It can operate at the frequency range of 82 - 116 GHz. The development of this new system is almost complete. We describe about the whole system in detail, which includes the receiver, the IF systems, the new spectrometers and the remote control systems. We also describe about the performances and the uniformity of the system and show the astronomical result.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
107 citations
"Gigabit Digital Filter Bank: Digita..." refers methods in this paper
...The ADCs were fabricated by improving a digital oscilloscope made by Sony/Tektronix Company (as developed in the BEARS project: Sunada et al. 2000)....
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TL;DR: In this paper, the results of the first dual-beam observations with VERA (VLBI Exploration of Radio Astrometry) were presented, and the results demonstrate the high capability of phase referencing, indicating that it is a promising tool for phase-referencing VLBI astrometry at 10 µas-level accuracy.
Abstract: We present the results of the first dual-beam observations with VERA (VLBI Exploration of Radio Astrometry). The observations of a pair of H2O maser sources, W 49N and OH 43.8−0.1, were carried out on 2002 May 29 and July 23, and fringes of the H2O maser lines at 22GHz were successfully detected. While the residual fringe phases of both sources showed rapid variations over 360 ◦ due to the atmospheric fluctuation, the differential phase between the two sources remained constant for 1 hour with an r.m.s. of 8 ◦ , demonstrating that the atmospheric phase fluctuation was effectively removed by dual-beam phase referencing. An analysis based on the Allan standard deviation reveals that the differential phase is mostly dominated by white phase noise, and the coherence function calculated from the differential phase shows that after phase referencing the fringe visibility can be integrated for an arbitrarily long time. These results demonstrate VERA’s high capability of phase referencing, indicating that it is a promising tool for phase-referencing VLBI astrometry at 10 µas-level accuracy.
67 citations
Additional excerpts
...The results of the first dual-beam observations with our developed VERA GDFB were presented by Honma et al. (2003), demonstrating that the atmospheric phase fluctuation was effectively removed by dual-beam phase referencing....
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