The Calibration of a Large Paraboloidal Antenna using a Cryogenic Black-Body Enclosure

The aperture efficiency of the 100-meter radiotelescope has been measured in the prime focus configuration at 5 GHz. Calibration was performed by inserting the feed-horn alternately in two specially designed black-body enclosures, the effective temperatures of which were provided by liquid nitrogen and liquid argon - a difference of 9.94 K. Radio sources of known flux density and brightness temperature were compared with the 9.94 K calibration, resulting in a 1.5 per cent uncertainty in the aperture efficiency. The sources of error are tabulated, and compared with those obtained by replacing the feed horn by waveguide loads.