The impact of automation on NBS noise temperature measurements

The accuracy of calibrating a thermal noise source using the National Bureau of Standards´ automated radiometer and cryogenic primary noise standards is typically ±2 percent, compared with ±3 percent for corresponding services that used manual radiometers and hot primary standards. Using the automated radiometer, a noise source can typically be calibrated at three frequencies in the time a manual radiometer requires to calibrate one. The automated radiometer contains a six-port reflectometer, and noise sources with reflection coefficients as great as 0.3 can be tolerated without significantly affecting the calibration accuracy. This makes it practical to use a single broad-band, coaxial noise standard from 0.03 to 14 GHz. The six-port reflectometer also makes it possible to calibrate sources with connectors different from those of the primary standard´s with almost no additional accuracy degradation.