PURPOSE:To attain to reduce a wt., an outer dimension and power consumption, by supplying the output of a sky horn and that of a standard noise source to each channel in common. CONSTITUTION:A first broad-band change-over switch 11, a second broad-band change-over switch 12 and a broad-band standard noise source 13 etc. are provided and, further, a comparing noise source 6, a second change-over switch 8 and a receiver 10 etc. are provided. For example, in the case of a channel A, because the noise source 13 is common to each channel, antenna temp. TA can be calculated according to formula (wherein T1 is the temp. of the antenna 1 from a sky horn, V1 is the output of the receiver 10 at the time of noise temp. T1, T3 is the output noise temp. of the noise source 13 made common to each channel and V3 is the output of the receiver 10 at the time of temp. T3 and the relations of T1TAT3 and V1VV3 are formed). By this method the standard noise source and first and third change-over switches necessary for each channel heretofore become unnecessary and the reduction of power consumption can be attained.
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