Abstract
A radiometer based on a new, modified null method is described. An additional, power-invariable noise signal is fed into the antenna channel from a generator in pulses of variable duration. A formula is derived that linearly relates this duration to the signal from the antenna, in which the noise temperatures of the semiconductor noise generator and the matched load act as two reference values. The radiometer has an unconventional measuring channel after the square-law detector. An instrument with the proposed scheme at a wavelength of 18 cm is described that is designed for operation in the field and optimization of remote studies of the natural environment. Its fluctuational sensitivity threshold is 0.03 K for an output-filter bandwidth of 1 Hz. The absolute measurement error is not more than 1 K for a maximum input signal and an ambient-temperature variation of from −25 to +35°C. The response nonlinearity is not over ±0.25 K for input noise temperatures of 75–315 K.
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