Design and implementation of PFB module with 10G network transmission system in CDAS2

Abstract

Digital baseband converters (DBBC) are among the core equipment in a very long baseline interferometry (VLBI) system, which undertakes missions of data acquisition, analog-to-digital conversion, and frequency selection. In order to enhance the measurement resolution of the Chinese VLBI Network (CVN), a new generation of DBBC named CDAS2 (the second-generation Chinese VLBI data acquisition system) has been developed. CDAS2 uses polyphase filter banks (PFB) and fast Fourier transform to convert signals from intermediate frequency to baseband. A high-speed sampling analog-to-digital converter is adopted to guarantee CDAS2’s broadband observation ability. In order to facilitate the broadband observation ability of CDAS2, a high-speed data transmission system is designed to transmit data from CDAS2 to a data recording server. The data transmission system includes a Mark5B formatter and a 10G network transmission system. We describe the detailed design of PFB and the data transmission system. We installed two CDAS2s in two radio astronomical telescopes of Shanghai Astronomical Observatory to carry out observation experiments for the radio source of 4C39.25. After processing with DiFX, we got interference fringes successfully. Our experiment demonstrates the validity and performance of CDAS2.