A measurement of the angular power spectrum of the anisotropy in the cosmic microwave background

We report on a measurement of the angular power spectrum of the anisotropy in the cosmic microwave background (CMB). The anisotropy is measured in 23 different multipole bands from l = 54 (approximate to 3 degrees) to l = 404 (approximate to 0 degrees.45) and in six frequency bands from 26 to 46 GHz over three observing seasons. The measurements are consistent from year to year. The frequency spectral index of the fluctuations (measured at low l) is consistent with that of the CMB and inconsistent with either dust or Galactic free-free emission. Furthermore, the observations of the MSAM1-92 experiment (Cheng et al. 1994) are repeated and confirmed. The angular spectrum shows a distinct rise from delta T-l drop [l(2l + 1)[\a(l)(m)\(2)]/4 pi](1/2) = 49(-5)(+8) mu K at l = 87 to delta T-l = 85(-8)(+10) mu K at l = 237. These values do not include an overall +/-14% (l sigma) calibration uncertainty. The analysis and possible systematic errors are discussed.