The Cosmic Anisotropy Telescope (CAT) has operated extremely successfully, producing the first image of CMB fluctuations on intermediate angular scales (Scott et al. 1996). Observations of the CAT1 field at 13.5, 15.5 and 16.5 GHz have given measurements of the CMB angular power spectrum on the smallest scales so far obtained, with important cosmological implications (see Sections 1.1.1 and 1.1.4).
Technically, the operation of the CAT has given us invaluable experience in the problems and realities of short-baseline interferometry, which have had a major impact on the design of the Very Small Array, currently under construction. There have been no major modifications to the CAT system in the past two years. A technical problem has been a gradual settling of the mechanical structure which necessitated the re-calibration of the pointing.
We have invested considerable effort in the problem of extracting the best cosmological results from interferometer data; following on from the work of Hobson et al.(1995) on estimation of Gaussian power spectra, we can now make estimates of the power in the CMB in given spectral windows without any assumptions as to the form of the power spectrum, and in the presence of contaminating Galactic signals of unknown spectral index. This is part of a broader programme of developing general analysis techniques for CMB data (see Section 1.1.4).