A New System Noise Measuring Method Using a 2-Bit Analog-to-Digital Converter

摘要

We propose a new measuring method for the system noise temperature, T_(sys), using a 2-bit analog-to-digital converter (ADC). Statistics of the digitized signal in a four-level quantization gives us information about the bias voltage and the variance, which reflects the power of the input signal. A comparison of the variances in hot and sky circumstances yields T_(sys) without a power meter. We performed experimental tests using the Kagoshima 6 m radio telescope and a 2-bit ADC. The linearity in the power–variance relation was better than 99% within the dynamic range of 10 dB. Digitally measured T_(sys) was in agreement with that of a conventional measurement with a power meter, although the temperatures differed by 1.8%, or less, for elevations of 10o–88o. No significant impact was found by the bias voltages within a range of -3.7% to +12.8% with respect to the threshold voltage. The proposed method is available for existing interferometers that have a multilevel ADC, and release us from troubles caused by power meters.