Definition, realization, and comparison of thermal noise standards

Since the state of the art for noise measurement was described in the 1967 Special Issue of PROCEEDINGS OF THE IEEE, several national standards laboratories outside the U.S. have built up thermal noise standards for the realization of the unit of noise power. Using a design for an above-ambient noise standard made of three distinct parts, a hot thermal noise standard for the waveguide band R 100 has been assembled at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. This primary standard enables the calibration of the excess noise ratio (ENR) of secondary transfer standards with an accuracy of ±0.02 dB. By means of a new broad-band coaxial radiometer this value has been transferred to coaxial systems with almost the same accuracy.