measurement is much less complicated to perform than the detection of local perturbations in the redshifted 21 cm background (which will be attempted in the near future by the Mileura Widefield Array \[MWA\], Low Frequency Array \[LOFAR\], Giant Metrewave Radio Telescope \[GMRT\], and Twenty-one Centimeter Array \[21CMA\]). Since the desired signal for the global measurement is the mean brightness temperature due to redshifted 21 cm emission (or absorption) over the entire sky, there is no need for high angular resolution or imaging. A single antenna tuned to the appropriate frequencies could reach the required sensitivity ($\sim25$ mK) within only one hour of integration time, assuming a reasonable spectral resolution of $\sim1$ MHz (equivalent to $\Delta
z\approx0.1$ at $z\approx8$). There is a fundamental complication with such an experiment, however, arising from the global nature of the signal. Since the expected redshifted 21 cm emission fills the entire sky, there is no ability to perform comparison switching between the target field and a blank field. The problem this causes is two-fold. First, it is difficult to separate the contribution to the measured spectrum due to the redshifted signal from that of any other all-sky emission, including Galactic synchrotron and free-free radiation, the 