A 33-GHz interferometer for cosmic microwave background observations on Tenerife

We describe a new high-sensitivity experiment for observing cosmic microwav e background (CMB) anisotropies. The instrument is a two-element interferom eter operating at 33 GHz with a similar to 3 GHz bandwidth. It is installed on the high and dry Teide Observatory site on Tenerife where successful be am-switching observations have been made at this frequency. Two realization s of the interferometer have been tested with element separations of 11.9 l ambda and 16.7 lambda. The resulting angular resolution of similar to 2 deg rees was chosen to explore the amplitude of CMB structure on the large angu lar scale side of the Doppler (acoustic) peak. It is found that observation s are unaffected by water vapour for more than 70 per cent of the time when the sensitivity is limited by the receiver noise alone. Observations over several months are expected to give an rms noise level of similar to 10-20 mu K covering similar to 100 resolution elements. Preliminary results show stable operation of the interferometer with the detection of discrete radio sources as well as the Galactic plane at Dec. = +41 degrees and -29 degree s.