6 research outputs found
Calibrating CHIME, A New Radio Interferometer to Probe Dark Energy
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit
interferometer currently being built at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral
hydrogen in the frequency range 400 -- 800\,MHz over half of the sky, producing
a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 --
2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that
will yield constraints on the BAO power spectrum and provide a test-bed for our
calibration scheme. I will discuss the CHIME calibration requirements and
describe instrumentation we are developing to meet these requirements
Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder
A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping
Experiment) is currently being commissioned at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical
interferometer designed to measure the large scale neutral hydrogen power
spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used
to measure the baryon acoustic oscillation (BAO) scale across this poorly
probed redshift range where dark energy becomes a significant contributor to
the evolution of the Universe. The instrument revives the cylinder design in
radio astronomy with a wide field survey as a primary goal. Modern low-noise
amplifiers and digital processing remove the necessity for the analog
beamforming that characterized previous designs. The Pathfinder consists of two
cylinders 37\,m long by 20\,m wide oriented north-south for a total collecting
area of 1,500 square meters. The cylinders are stationary with no moving parts,
and form a transit instrument with an instantaneous field of view of
100\,degrees by 1-2\,degrees. Each CHIME Pathfinder cylinder has a
feedline with 64 dual polarization feeds placed every 30\,cm which
Nyquist sample the north-south sky over much of the frequency band. The signals
from each dual-polarization feed are independently amplified, filtered to
400-800\,MHz, and directly sampled at 800\,MSps using 8 bits. The correlator is
an FX design, where the Fourier transform channelization is performed in FPGAs,
which are interfaced to a set of GPUs that compute the correlation matrix. The
CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed
to detect the BAO feature and constrain the distance-redshift relation.Comment: 20 pages, 12 figures. submitted to Proc. SPIE, Astronomical
Telescopes + Instrumentation (2014
Characterization of the John A. Galt telescope for radio holography with CHIME
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will measure the
21 cm emission of astrophysical neutral hydrogen to probe large scale structure
at redshifts z=0.8-2.5. However, detecting the 21 cm signal beneath
substantially brighter foregrounds remains a key challenge. Due to the high
dynamic range between 21 cm and foreground emission, an exquisite calibration
of instrument systematics, notably the telescope beam, is required to
successfully filter out the foregrounds. One technique being used to achieve a
high fidelity measurement of the CHIME beam is radio holography, wherein
signals from each of CHIME's analog inputs are correlated with the signal from
a co-located reference antenna, the 26 m John A. Galt telescope, as the 26 m
Galt telescope tracks a bright point source transiting over CHIME. In this work
we present an analysis of several of the Galt telescope's properties. We employ
driftscan measurements of several bright sources, along with background
estimates derived from the 408 MHz Haslam map, to estimate the Galt system
temperature. To determine the Galt telescope's beam shape, we perform and
analyze a raster scan of the bright radio source Cassiopeia A. Finally, we use
early holographic measurements to measure the Galt telescope's geometry with
respect to CHIME for the holographic analysis of the CHIME and Galt
interferometric data set
Development of a low-noise wide-band phased-array feed
Low-noise phased-array feeds are a new way to expand the field of view of radio telescopes at centimetre wavelengths. First generation engineering demonstrators of this technology have been constructed and tested by several institutes worldwide. The development of second-generation phased-array feeds is now underway. We describe one effort to design and build an astronomy-capable phased-array feed using techniques to reduce front-end noise and increase system bandwidth.Peer reviewed: YesNRC publication: Ye
Base Band Data for Testing Interference Mitigation Algorithms
Digital signal processing is one of many valuable tools for suppressing unwanted signals or interference. Building hardware processing engines seems to be the way to best implement some classes of interference suppression but is, unfortunately, expensive and time consuming, especially if several mitigation techniques need to be compared. Simulations can be useful, but are not a substitute for real data. The CSIRO Australia Telescope National Facility has recently commenced a "software radio telescope" project designed to ll the gap between dedicated hardware processors and pure simulation. In this approach, real telescope data are recorded coherently, then processed o-line. This paper summarises the current contents of a freely available database of base band recorded data that can be used to experiment with signal processing solutions. It includes data from the following systems: single dish multi-feed receiver, single dish with reference antenna, and an array of six 22-meter antennas with and without a reference antenna. Astronomical sources such as OH masers, pulsars and continuum sources subject to interfering signals were recorded. The interfering signals include the US Global Positioning System (GPS) and Russian equivalent GLONASS, television, microwave links, a low Earth orbit (LEO) satellite, various other transmitters, and signals leaking from local telescope systems with fast clocks. Data are available on compact disk for use in general purpose computers, or as an input to laboratory hardware prototypes. Keywords: instrumentation: detectors, interferometers, techniques: interferometric, methods: data analysis