The calibration horn antenna

The construction and history of the calibration horn antenna, a large standard-gain horn at the National Radio Astronomy Observatory, Green Bank, West Virginia, are discussed. Construction of the horn began in 1958. Its purpose was to make absolute measurements by observing a strong source directly with a standard-gain horn antenna. The discussion covers: the antenna design; fabricating and erecting the horn; early electronics and first results; thermal calibrations and corrections to the data; data collection and reduction related work done with the Bell Telephone Laboratories horn; measurements in 1968-78; observations at 820 MHz; comparison with the EB map; radio source Cas A flux density at 820 MHz; and interferometric measurements. The observations are summarized and discussed.<>