A measurement of the angular power spectrum of the cosmic microwave background from l=100 to 400

We report on a measurement of the angular spectrum of the cosmic microwave background (CMB) between l approximate to 100 and I approximate to 400 made at 144 GHz from Cerro Toco in the Chilean altiplano. When the new data are combined with previous data at 30 and 40 GHz taken with the same instrumen t observing the same section of sky, we find (1) a rise in the angular spec trum to a maximum with delta T-l approximate to 85 mu K at l approximate to 200 and a fall at I > 300, thereby localizing the peak near I approximate to 200, and (2) that the anisotropy at I approximate to 200 has the spectru m of the CMB.