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A two element interferometer prototype for the Canadian Hydrogen Intensity Mapping Experiment Davis, Gregory


The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will measure the distribution of neutral hydrogen in the universe to constrain dark energy models. A two element radio interferometer operating between 425 and 850 MHz was built at the Dominion Radio Astrophysical Observatory as a CHIME technology prototype. The system temperature is approximately 80 K midband, of which almost 40 K is caused by feed loss and ground spill. A band defining filter used in the receiver allows the signal to be alias sampled at 850 MHz and unfolded to 425-850 MHz. Delayed crosstalk between channels in the interferometer causes prominent spectral ripple with 3.8 MHz period in the cross correlations. Further baseline spectral ripple with 41 MHz period is caused by standing waves between the reflector and the feed ground plane. Sky maps between declinations 52° < δ < 73° over the full frequency band were made using a single dish. The accuracy of the maps is limited predominantly by gain fluctuation in the receiver caused by temperature, 1/f amplifier gain variation, and radio frequency interference. Principal component analysis is demonstrated as a foreground removal technique.

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