We report the results of an effort to measure the low frequency portion of the spectrum of the Cosmic Microwave Background Radiation ( CMB ) , using a balloon-borne instrument called ARCADE ( Absolute Radiometer for Cosmology , Astrophysics , and Diffuse Emission ) .
These measurements are to search for deviations from a thermal spectrum that are expected to exist in the CMB due to various processes in the early universe .

The radiometric temperature was measured at 10 and 30 GHz using a cryogenic open-aperture instrument with no emissive windows .
An external blackbody calibrator provides an in situ reference .
A linear model is used to compare the radiometer output to a set of thermometers on the instrument .
The unmodeled residuals are less than 50 mK peak-to-peak with a weighted RMS of 6 mK .
Small corrections are made for the residual emission from the flight train , atmosphere , and foreground Galactic emission .
The measured radiometric temperature of the CMB is 2.721 \pm . 010 K at 10 GHz and 2.694 \pm 0.032 K at 30 GHz .