Instrumentation
A 1.3-metre primary mirror, along with a smaller secondary and tertiary mirror, was used to focus the microwaves onto the feed horns. The feed horns have spectral bands centred at 150, 240 and 420 GHz with a resolution of 10 arcminutes. A bolometer array consisting of 16 NTD-Ge Thermistors measured the incident radiation.
The detector array was cooled down to 100 mK via a four stage refrigeration process. Liquid nitrogen cooled the outer layer of radiation shielding and He-4 was used to cool the two other layers down to a temperature of 2-3 K. Finally liquid He-3 cooled the array down to operation temperature. The shielding, together with the properties of the feed horns, gave a superb sensitivity of 40 μV/sec^1/2.
Two CCD cameras where used to provide accurate measurements of the telescope's orientation. The first wide-field camera pointed towards Polaris and gave a coarse orientation up to 15 arcminutes. The other camera was mounted in the primary focus and gives an accuracy of 0.5' for stars brighter than 6th magnitude, which in total gives an accurate position tracking of 10' for the telescope and hence of the microwaves.
For pointing the telescope, four motors were used.
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