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This paper reviews the National Bureau of Standards (NBS) preision noise measurements program for antenna systems which have been made using Cassiopeia A and the moon. The Earth Terminal Measurement System (ETMS) was developed by NBS to make measurements of figure of merit (G/T), and the noise equivalent flux (NEF). The accuracy of the noise measurements are, typically, between 5 and 15 percent for systems with antenna gains between 51 and 65 dB and frequencies between 1 and 10 GHz. Key wordsÂ¿antenna gain; antenna half-power beamwidth; atmospheric loss; Cassiopeia A; earth terminal measurement system; figure of merit; moon; noise equivalent flux; noise measurement; radio stars; satellite communication.