cm contribution to the measured spectrum along with the residuals after a seventh-order polynomial fit is removed from a simulated sky spectrum. This is the method used for the preliminary EDGES measurements. An advantage of this approach for global reionization experiments is that, given sufficient sensitivity, even a null result could still constrain $\dot{\bar{x}}_{HI}(z)$ and, thereby, distinguish between slow and fast reionization scenarios.

Experiment Design {#s_edges_system}
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By focusing (at least initially) on confirming or ruling out a fast reionization scenario, the design of the EDGES system is able to be relatively simple. The primary need is to reduce any instrumental or systematic contributions to the measured power spectrum that vary rapidly with frequency, since these could be confused with a sharp feature in the spectrum due to a fast reionization of the IGM. Such contributions could be due to terrestrial transmitters, reflections of receiver noise or sky noise from nearby objects, undesirable resonances within the electronics or the radio-frequency interference (RFI) enclosures, or spurious signals introduced by the digital sampling system. In this section, we provide an overview of the experimental design and setup, highlighting aspects that are relevant to reducing the effects of both the external and internal 