A New System Noise Measurement Method Using a 2-bit Analog-To-Digital Converter

TL;DR

This paper introduces a novel method to measure system noise temperature using a 2-bit ADC, eliminating the need for traditional power meters and demonstrating high accuracy through telescope experiments.

Contribution

The paper presents a new technique leveraging 2-bit ADC digitization statistics to measure system noise temperature without additional power measurement devices.

Findings

Linearity in power-variance relation exceeds 99% within 10 dB range

Measured $T_{sys}$ agrees within 1.8% of conventional methods

Method is unaffected by bias voltage variations within tested range

Abstract

We propose a new method to measure the system noise temperature, $T_{\rm sys}$, using a 2-bit analog-to-digital converter (ADC). The statistics of the digitized signal in a four-level quantization brings us information about the bias voltage and the variance, which reflects the power of the input signal. Comparison of the variances in {\it hot} and {\it sky} circumstances yields $T_{\rm sys}$ without a power meter. We performed test experiments using the Kagoshima 6-m radio telescope and a 2-bit ADC to verify this method. Linearity in the power-variance relation was better than 99% within the dynamic range of 10 dB. Digitally measured $T_{\rm sys}$ coincided with that of conventional measurement with a power meter in 1.8-% difference or less for elevations of $10^{\circ} - 88^{\circ}$. No significant impact was found by the bias voltages within the range between -3.7 and +12.8% with respect to the threshold voltage. The proposed method is available for existing interferometers that have a multi-level ADC, and release us from troubles caused by power meters.