Interferometry and Synthesis in Radio Astronomy

Thompson, Alexander; Moran, J. M.; Swenson, George W.

doi:10.1002/9783527617845

Cited by 951 publications

(562 citation statements)

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“…The switching period for each group is different and is a fraction of the time period for which the data is integrated. This implies that the crosstalk signal will get averaged to zero as they will be correlated positively and negatively during either half of the integration period [18]. This switching sequence is subsequently removed at the output of the sampler (using the same Walsh function), thereby also eliminating any errors due to possible DC offsets in the A/D convertors.…”

Section: Walsh Switchingmentioning

confidence: 99%

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The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph

Ramesh

Rajan

Sastry³

2006

Exp Astron

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A low frequency (40-150 MHz) radioheliograph for observations of the solar corona is in operation for the last few years at the Gauribidanur radio observatory, about 100 km north of Bangalore. The array has 32 antenna groups and a 1-bit digital correlator system consisting of 1024 channels is used as the back-end receiver. This paper describes the latter and results of the associated system tests.

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Section: Walsh Switchingmentioning

confidence: 99%

“…The necessary delay is implemented under the control of a computer up to a maximum of ≈7.5 μs in steps of ∼0.5 μs. For the 2.04 MHz sampling rate, the maximum delay error (≈0.25 μs) causes a coherence loss of about 10% for a 1 MHz bandwidth [18].…”

Section: The 1024 Channel Digital Correlatormentioning

confidence: 99%

The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph

Ramesh

Rajan

Sastry³

2006

Exp Astron

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“…For instance, if there is a 10 • phase drift in a local oscillator at a given site, then the down-converted data will have a 10 • phase drift as well. In addition, there is a phase shift caused by turbulence in the atmosphere (Thompson et al, 2001). If atmospheric phase instabilities are the dominant source of phase noise in the measurements, then this disturbance can be calibrated out by the use of one or more phase calibration sources (Walker, 1999).…”

Section: Introductionmentioning

confidence: 99%

Local Oscillator Distribution Using A Geostationary Satellite

2004

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A satellite communication system suitable for distribution of local oscillator reference signals for a widely spaced microwave array has been developed and tested experimentally. The system uses a round-trip correction method to remove effects of atmospheric fluctuations and radial motion of the satellite. This experiment was carried out using Telstar-5, a commercial Ku-band geostationary satellite. A typical Ku-band satellite has uplink and downlink capacity at 14-14.5 GHz and 11.7-12.2 GHz, respectively. For this initial experiment, both earth stations were located at the same site to facilitate direct comparison of the received signals. The local oscillator reference frequency was chosen to be 300 MHz and was sent as the difference between two Ku-band tones. The residual error after applying the round trip correction has been measured to be better than 3 ps for integration times ranging from 1 to 2000 s. For integration times greater than 500 s, the system outperforms a pair of hydrogen masers with the limitation believed to be ground-based equipment phase stability. The idea of distributing local oscillators using a geostationary satellite is not new; several researchers experimented with this technique in the eighties, but the achieved accuracy was 3 to 100 times worse than the present results. Since then, the cost of both leased satellite bandwidth and the Ku-band ground equipment has dropped substantially and the performance of various components has improved. An important factor is the availability of narrow bands which can be leased on a communications satellite. We lease three 100 kHz bands at approximately one hundredth the cost of a full 36 MHz-wide transponder. Further tests of the system using terminals separated by large distances and comparison tests with two hydrogen masers and radio interferometry of astronomical objects are needed.

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“…The resulting estimates of spatio-temporal and spectral correlations between responses of pairs of elements can be used to recover the desired information on the strength and distribution of radio emission within the common field of view [8] using standard post-processing software. Thus the signal of interest is statistical in nature, resulting from a minute level of mutual coherence arising from weak celestial signals buried in noise.…”

Section: Introductionmentioning

confidence: 99%

A high speed networked signal processing platform for multi-element radio telescopes

Prasad

Subrahmanya

2011

Exp Astron

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A new architecture is presented for a Networked Signal Processing System (NSPS) suitable for handling the real-time signal processing of multielement radio telescopes. In this system, a multi-element radio telescope is viewed as an application of a multi-sensor, data fusion problem which can be decomposed into a general set of computing and network components for which a practical and scalable architecture is enabled by current technology. The need for such a system arose in the context of an ongoing program for reconfiguring the Ooty Radio Telescope (ORT) as a programmable 264-element array, which will enable several new observing capabilities for large scale surveys on this mature telescope. For this application, it is necessary to manage, route and combine large volumes of data whose real-time collation requires large I/O bandwidths to be sustained. Since these are general requirements of many multi-sensor fusion applications, we first describe the basic architecture of the NSPS in terms of a Fusion Tree before elaborating on its application for the ORT. The paper addresses issues relating to high speed distributed data acquisition, Field Programmable Gate Array (FPGA) based peer-topeer networks supporting significant on-the fly processing while routing, and providing a last mile interface to a typical commodity network like Gigabit Ethernet. The system is fundamentally a pair of two co-operative networks, among which one is part of a commodity high performance computer cluster 2 Exp Astron (2011) 31: and the other is based on Commercial-Off The-Shelf (COTS) technology with support from software/firmware components in the public domain.

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Interferometry and Synthesis in Radio Astronomy

Cited by 951 publications

References 0 publications

The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph

The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph

Local Oscillator Distribution Using A Geostationary Satellite

A high speed networked signal processing platform for multi-element radio telescopes

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