21 cm observations: calibration, strategies, observables
  This chapter aims to provide a review of the basics of 21 cm interferometric
observations and its methodologies. A summary of the main concepts of radio
interferometry and their connection with the 21 cm observables - power spectra
and images - is presented. I then provide a review of interferometric
calibration and its interplay with foreground separation, including the current
open challenges in calibration of 21 cm observations. Finally, a review of 21
cm instrument designs in the light of calibration choices and observing
strategies follows.
