A Method of Calibrating Centimetric Radiometers Using a Standard Noise Source

In order to compare radio-astronomical measurements of power flux observed on different occasions at different wavelengths, special attention must be paid to methods of calibration. A method is described which is suitable for a centimetric radiometer measuring antenna temperature over a range of 0 to 1000°K or more with an accuracy of about 1°K. The power received by the radiometer is compared with that from a CV1881 argon discharge tube fed through a precision attenuator. An additional fixed amount of power is added to that of the radiometer to ensure that the effective temperature is above that of the room. The intensity of solar radiation at λ = 10.5 cm was measured by this method during the eclipse of June 30, 1954. The scale of the chart recording the radiometer output was effectively increased by adjusting the attenuator in steps each time maximum deflection was attained corresponding to about 20°K change of antenna temperature. Finally, to measure the brightness temperature of the uneclipsed sun, the received power from the sun was compared with that from a known external noise source consisting of a horn radiator fed by a CV1881 argon discharge tube.