206 research outputs found
A Digital Calibration Source for 21cm Cosmology Telescopes
Foreground mitigation is critical to all next-generation radio
interferometers that target cosmology using the redshifted neutral hydrogen 21
cm emission line. Attempts to remove this foreground emission have led to new
analysis techniques as well as new developments in hardware specifically
dedicated to instrument beam and gain calibration, including stabilized signal
injection into the interferometric array and drone-based platforms for beam
mapping. The radio calibration sources currently used in the literature are
broad-band incoherent sources that can only be detected as excess power and
with no direct sensitivity to phase information. In this paper, we describe a
digital radio source which uses Global Positioning Satellite (GPS) derived time
stamps to form a deterministic signal that can be broadcast from an aerial
platform. A copy of this source can be deployed locally at the instrument
correlator such that the received signal from the aerial platform can be
correlated with the local copy, and the resulting correlation can be measured
in both amplitude and phase for each interferometric element. We define the
requirements for such a source, describe an initial implementation and
verification of this source using commercial Software Defined Radio boards, and
present beam map slices from antenna range measurements using the commercial
boards. We found that the commercial board did not meet all requirements, so we
also suggest future directions using a more sophisticated chipset.Comment: 13 pages, 5 figures, published in Journal of Astronomical
Instrumentatio
The GMRT Search for Reionization
We present an overview for the reionization search at GMRT. The forecast
sensitivities are promising for an early detection. RFI mitigation has been
successful. Several hundred hours of telescope time have already been invested
in this ongoing effort, and analysis of the data is in progress.Comment: 7 pages, invited talk at Arecibo conference "The Evolution of
Galaxies through the Neutral Hydrogen Window
A GPU-based Correlator X-engine Implemented on the CHIME Pathfinder
We present the design and implementation of a custom GPU-based compute
cluster that provides the correlation X-engine of the CHIME Pathfinder radio
telescope. It is among the largest such systems in operation, correlating
32,896 baselines (256 inputs) over 400MHz of radio bandwidth. Making heavy use
of consumer-grade parts and a custom software stack, the system was developed
at a small fraction of the cost of comparable installations. Unlike existing
GPU backends, this system is built around OpenCL kernels running on
consumer-level AMD GPUs, taking advantage of low-cost hardware and leveraging
packed integer operations to double algorithmic efficiency. The system achieves
the required 105TOPS in a 10kW power envelope, making it among the most
power-efficient X-engines in use today.Comment: 6 pages, 5 figures. Accepted by IEEE ASAP 201
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