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Using the Cosmic Background Imager (CBI), a 13-element interferometer array operating in the 26–36 GHz frequency band, we have observed 40 deg 2 of sky in three pairs of fields, each∼ 145′× 165′, using overlapping pointings (mosaicking). We present images and power spectra of the cosmic microwave background radiation in these mosaic fields. We remove ground radiation and other low-level contaminating signals by differencing matched observations of the fields in each pair. The primary foreground contamination is due to point sources (radio galaxies and quasars). We have subtracted the strongest sources from the data using higher resolution measurements, and we have projected out the response to other sources of known position in the power spectrum analysis. The images show features on scales∼ 6 &arcmin;–15 &arcmin;, corresponding to masses∼(5–80)× 10 14 M⊙ at the surface of last …