The High-Z All-Sky Spectrum Experiment

The Cosmic Dawn (z~30 to z~10) is the observationally elusive time period in the history of the universe when the first stars ignited and started filling the universe with their light, thereby changing the intergalactic medium (IGM) around them. The UV light from the first stars left an imprint on the 21-cm cosmological signal, which could be detected observationally as a dip in the global 21-cm temperature brightness spectrum. The death of the first stars also effected the 21-cm signal by heating up the gas in the IGM, leading to a rise in the 21-cm temperature brightness temperature. The exact location and shape of the cosmic signal caused by the dip and rise of the 21-cm temperature brightness during this time period is still uncertain, due to

insufficient observational data. Although the EDGES team has reported a potential detection of this cosmological signal, their detection has not be confirmed. Other

groups with vastly different observational systems need to measure the signal for the cosmological community to be convinced of the detection. Our group has developed the High-Z system to measure this cosmological signal

from the period of the Cosmic Dawn. The High-Z system measures the global average of the 21-cm temperature brightness spectrum but is very different from the systems

used by other 21-cm observational groups. High-Z is the only system to use an unmatched network to measure the 21-cm cosmological signal. In this thesis, I describe

the calibration of the High-Z system and the interesting effects that result from the purposeful impedance mismatch of our system. The large impedance mismatch in our system leads to certain effects being magnified, which might not be otherwise noticed in a matched network. The focus of this thesis is primarily on the absolute calibration of the High-Z

system, along with the development and testing of the different methods for experimentally measuring the noise contribution of the first amplifier in our electronic chain.

The complete characterization of the noise properties of the first amplifier, which is the largest contributor of noise in our system, is crucial to the correct calibration of the High-Z system. In addition to calibration, I cover the deployments of the High-Z system in the field on three separate occasions and develop a data analysis pipeline for processing the data from the field.