OCTAD-S: Digital Fast Fourier Transform Spectrometers by FPGA

TL;DR

The paper presents OCTAD-S, a flexible digital FFT spectrometer built with FPGA and ADC modules, capable of high-speed, dead-time-free spectral analysis up to 8 GHz, demonstrated through laboratory and solar observation tests.

Contribution

It introduces a modular FPGA-based FFT spectrometer with high sampling rates and wide dynamic range, enabling versatile and stable radio frequency spectral measurements.

Findings

Achieved dead-time-free spectral recording every 8 ms.

Demonstrated stable spectroscopy with wide dynamic range.

Successfully tested with solar radio burst observations.

Abstract

We have developed a digital fast Fourier transform (FFT) spectrometer made of an analog-to-digital converter (ADC) and a field-programmable gate array (FPGA). The base instrument has independent ADC and FPGA modules, which allow us to implement different spectrometers in a relatively easy manner. Two types of spectrometers have been instrumented, one with 4.096 GS/s sampling speed and 2048 frequency channels and the other with 2.048 GS/s sampling speed and 32768 frequency channels. The signal processing in these spectrometers has no dead time and the accumulated spectra are recorded in external media every 8 ms. A direct sampling spectroscopy up to 8 GHz is achieved by a microwave track-and-hold circuit, which can reduce the analog receiver in front of the spectrometer. Highly stable spectroscopy with a wide dynamic range was demonstrated in a series of laboratory experiments and test observations of solar radio bursts.