  We present sensitivity forecasts for the PAST 21cm reionization observations
and compare these with the measured sensitivity of a prototype array. We
discuss the likely epoch-of-reionization structures and the redshifts that can
be observed, and conclude that a 10,000 antenna PAST will be able to image
ionized structures with its 1 million pixel map at 6<z<20. The angular scales
of the images to be produced span from 5 arc minutes to 10 degrees. The effect
of potential foreground contaminants are analyzed. All known extra-terrestial
foregrounds have power law continuum spectra, and can be modeled and cleanly
separated. We present results of observations using the prototype, which verify
the estimated sensitivities and provide data on astronomical foregrounds. The
same sample allows real-world measurement of man-made interference, of meteor
scatter propagation, and of ionospheric variation. These data are also used to
verify our large angle map making algorithms.
