Observations of the microwave background on a scale of 8 deg. I - The observing system

Davies, R. D.; Watson, R. A.; Daintree, E. J.; Hopkins, J.; Lasenby, A. N.; Sanchez-Almeida, J.; Beckman, J. E.; Rebolo, R.
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Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 258, no. 3, p. 605-615.

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A sensitive observing system for observing the cosmic microwave background on an angular scale of 8 deg is described. This angular scale is appropriate for studies of intrinsic fluctuations in the CMB generated by gravitational potential fluctuations (the Sachs-Wolfe effect). The beam-switching system employs low-noise and broadband cryogenically cooled receivers. A major improvement in the stability of the system has resulted from triple-beam operation which removes the effect of atmospheric water vapour and ambient temperature changes to a level of several millikelvin on a single scan. The evaluation and assessment of this system operating at an elevation of 2400 m on Tenerife is described. Results for an RA circle at Dec. = 40 deg are shown; these reach a sensitivity of better than 100 micro-K in an 8.4 deg beam.