In keeping with the discussion of previous sections, we discuss these below in order of increasing angular size. It should be borne in mind that over this range of angular scales many models of galaxy formation predict angular spectra in the temperature fluctuations which are not well approximated by a Gaussian distribution. Thus, over this range of scales the observations must be compared to specific models in order to estimate the expected variance in sky temperature as given by Equation 3. We follow this practice below, but caution the reader that limits and expected values of the sky variance derived by this method cannot readily be compared to theoretically predicted levels of the sky fluctuations. The receivers used SIS mixers to achieve low noise levels operating at 43 GHz with a bandwidth of 500 MHz.
Interferometric observations have a number of advantages over single dish observations.
The most important of these are the elimination to high order of sources of systematic noise which are spread over large angles, such as ground spillover and atmospheric gradients on large angular scales. The observations were carried out in January and February 1987. The output was therefore equivalent to a double switching experiment, with the first level of switching being done by the interferometer at a frequency comparable to the reciprocal of the bandwidth. This double differencing eliminates long term drifts in the signal level caused by instrumental drifts in gain and offset and atmospheric changes. Observations were made almost continuously over a 15-day period.