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The Large-Aperture Experiment to Detect the Dark Age (LEDA) was designed todetect the predicted O(100)mK sky-averaged absorption of the Cosmic MicrowaveBackground by Hydrogen in the neutral pre- and intergalactic medium just afterthe cosmological Dark Age. The spectral signature would be associated withemergence of a diffuse Ly$\alpha$ background from starlight during 'CosmicDawn'. Recently, Bowman et al. (2018) have reported detection of this predictedabsorption feature, with an unexpectedly large amplitude of 530 mK, centered at78 MHz. Verification of this result by an independent experiment, such as LEDA,is pressing. In this paper, we detail design and characterization of the LEDAradiometer systems, and a first-generation pipeline that instantiates a signalpath model. Sited at the Owens Valley Radio Observatory Long Wavelength Array,LEDA systems include the station correlator, five well-separated redundant dualpolarization radiometers and backend electronics. The radiometers deliver a30-85MHz band (16<z<34) and operate as part of the larger interferometricarray, for purposes ultimately of in situ calibration. Here, we report on theLEDA system design, calibration approach, and progress in characterization asof January 2016. The LEDA systems are currently being modified to improveperformance near 78 MHz in order to verify the purported absorption feature.

Design and characterization of the Large-Aperture Experiment to Detect the Dark Age (LEDA) radiometer systems