Signals conversion systems of VLBI “Quasar” network

The paper is devoted to modern signals conversion systems which are used in radio interferometric “Quasar " network. The relations between coordinate-time measurements accuracy and system signal conversion parameters are showed. The structure, basic principles and performance of the regular system R1002M, which is developed in IAA RAS, with data stream 2 Gbit/s are considered. The 16-th channels system R1002M works in intermediate frequency range 0,1-1 GHz, and provides acquisition up to 2 Gbits/s data rate in widespread format VSI-H. Since 2011 the systems R1002M working on “Quasar " network radio telescopes as regular equipment, and are used in all VLBI observations carried out by domestic and foreign programs, including the trajectory measurements of spacecraft. The analysis of the operation results of R1002M are presented for last few years. The positive effect of replacing of foreign systems on the R1002M’s are showed. Its due to the reduction of radio interferometer instrumental sensitivity losses, improvement of linearity and stability of the channels phase characteristics by using digital signal processing. To equip new radio telescopes with small antennas (12-13 m) diameter the new broadband acquisition system (BRAS) was developed. It is designed for accommodation directly on the antenna, which allows to refuse high frequency feeders and transmit digital date streams through optical fiber by 10G Ethernet interface. The system is constructed by a modular design and consists of eight identical digital signal conversion channels, working in intermediate frequency range of 11,5 GHz with 512 MHz bandwidth. It provides formation of information data flow in the VDIF international format with a total data stream up to 16 Gbit/s. The structure, element base, description of the system, comparison with foreign analogues and also the results of development type BRAS testing on existing radio telescopes are given. Tests confirmed the high parameters of the developed system that allows you to significantly increase the sensitivity of the radio interferometer and increase the number of available observations for cosmic radio sources.