Bandpass calibration of a wideband spectrometer using coherent pulse injection

TL;DR

This paper introduces a simple time domain method using coherent pulse injection for accurate bandpass calibration of wideband spectrometers, demonstrated with a digital setup and applied at a radio telescope.

Contribution

It presents a novel variation of impulse response calibration using pulse trains and demonstrates its effectiveness with a digital system at a radio telescope.

Findings

Effective broadband response determination up to 1 GHz

Coherent pulse train improves calibration precision

Successful application at Parkes radio telescope

Abstract

We present a relatively simple time domain method for determining the bandpass response of a system by injecting a nanosecond pulse and capturing the system voltage output. A pulse of sub-nanosecond duration contains all frequency components with nearly constant amplitude up to 1 GHz. Hence, this method can accurately determine the system bandpass response to a broadband signal. In a novel variation on this impulse response method, a train of pulses is coherently accumulated providing precision calibration with a simple system. The basic concept is demonstrated using a pulse generator-accumulator setup realised in a Bedlam board which is a high speed digital signal processing unit. The same system was used at the Parkes radio telescope between 2-13 October 2013 and we demonstrate its powerful diagnostic capability. We also present some initial test data from this experiment.