A 10.24-GHz-wide digital spectrometer array system for LMT-FINER: system design and laboratory performance verification

TL;DR

This paper introduces a novel 10.24-GHz-wide digital spectrometer array system designed for the LMT-FINER telescope, demonstrating laboratory performance suitable for wide-band spectroscopy of high-redshift galaxies.

Contribution

It presents a new digital spectrometer system with wide bandwidth, digital sideband separation, and high dynamic range, optimized for astronomical observations of early galaxies.

Findings

Achieved sideband rejection up to 25 dB.

Demonstrated an Allan time of at least 100 seconds.

Showed capability for instant wide-band spectroscopy.

Abstract

For efficient spectroscopic redshift identification of early galaxies in the northern hemisphere, we aim to combine the Large Millimeter Telescope (LMT) with a wide-band heterodyne receiver, FINER, which will cover radio frequencies of 120--360 GHz and offer a 3--21 GHz intermediate frequency (IF) per sideband and polarization. To take full advantage of such wide IFs, we present a novel 10.24-GHz-wide digital spectrometer, DRS4 (Elecs Industry Co., Ltd.). It incorporates 20.48 Gsps samplers with an FPGA-based digital signal processing module. To mitigate the noise contamination from the image sideband, it is equipped with a digital sideband separation function to improve the sideband rejection up to 25 dB. Laboratory performance evaluations show that it exhibits an Allan time of at least ~100 s and a total power dynamic range of at least 7 dB. These results demonstrate its capability of instantaneously wide-band spectroscopy toward high-redshift galaxies with position-switching observations.