Precision Broad-Band RE-Switched Radiometer for the Megahertz and Lower Gigahertz Range with IF Attenuator

A broad-band coaxial RF-switched radiometer with IF attenuator used for the comparison of unknown noise sources with a hot thermal noise standard is described. The total relative systematic 1σ uncertainty, theoretically and experimentally obtained during calibration of a typical noise source by means of this radiometer, is given. Compared with the total relative systematic uncertainty of the most precise RF-switched RF attenuation radiometer which cannot be realized for megahertz frequencies, and for low gigahertz frequencies in narrow-band systems only, the total relative systematic 1σ uncertainty of the broad-band IF attenuation radiometer is increased by less than 0.01 dB.