A data acquisition system for very-long-baseline interferometers

A data-acquisition system designed for very-long-baseline interferometers is connected to the outputs of cryoelectronic radio astronomy receivers, selects signals in specified frequency bands, and converts them into digital data flows for their recording or transmission through telecommunication channels. The system has two inputs and may contain from two to eight base-band converters with an intermediate frequency tuning range of 100-1000 MHz with a 10-kHz step. These converters transform input signals into video frequencies (up to 16 MHz) and separate signals of the upper and lower side bands with an image rejection of >23 dB. The distortions and loss in the phase coherence of the received noise signals are minimized thanks to the equalizing of the amplitude and phase responses of the amplifiers and selectors, and the good spectral characteristics of the local oscillators of the base-band converters. The data-acquisition system is controlled by a PC or the Mark IV Field System program (now used internationally in the pursuit of radio interferometry), which is installed in the radio telescope's central computer using an RS-232 interface. The prototype of such a system is used as standard equipment for conducting observations on the Svetloye-Zelenchukskaya radio interferometer. The first lot of such systems for the development of a network of radio interferometers has been produced.