The Experiment to Detect the Global EoR Signature (EDGES) is a pioneering NSF-funded ground-based effort to measure the sky-average 21-cm radiation from neutral hydrogen in the intergalactic medium (IGM) at redshifts 27 > z > 6. These redshifts correspond to the period of formation of the first stars, galaxies, and black holes, as well as their reionization of the IGM. For the 21-cm radiation, these redshifts are accessed by measuring in the radio frequency range 50-200 MHz.Photo of the EDGES instrument

EDGES represents a pathfinder for the Moon-orbiting DARE mission, as well as for the Moon-based low-frequency cosmology radio telescopes under study by NESS. 

EDGES has conducted measurements since 2007, and is located at the Murchison Radioastronomy Observatory in the desert of Western Australia to take advantage of its low levels of artificial radio-frequency interference (RFI). 

Along with RFI, one of the most significant challenges in this measurement corresponds to distinguishing the very weak 21-cm signal (< 500 mK) from the strong diffuse foregrounds, which are between hundreds and thousands of Kelvin. These foregrounds impose the requirement of instrumental calibration at the level of about 1 part in 10,000, in order to reach enough sensitivity for detection. The current EDGES sensitivity is comparable to this requirement, which has enabled EDGES to place the tightest constraints to date on the global 21-cm signal from the early Universe. See news and a recent publication.