Spectral Line Registration Backend Based on USRP X300 Software Defined Radio

This paper presents implementation of spectrometer based on off-the-shelf software defined radio (SDR) Ettus Research USRP X300 equipped with TwinRX daughterboard. Parallelized software, employing Fast Fourier Transform (FFT), is developed which allows two channel spectrum processing in real time with bandwidths up to 50MHz per channel, sample resolution of 14 bits and FFT lengths up to 32k points. Measured Allan stability time of the spectrometer is at least 750 sin laboratory environment. Software has network server-type interface that allows to conveniently integrate the spectrometer in radio telescope observation control and monitoring system with versatility of SDR allowing to implement various observation modes, for example, total power detection functionality with high frequency selectivity, which allows to carry continuum amplitude calibration in presence of near-by radio frequency interference. Presented spectrometer has been successfully integrated and used at RT-32 and RT-16 radio telescopes of Ventspils International Radio Astronomy Centre.