Gino Tuccari

Recent Progress in the VLBI2010 Development

From October 2003 to September 2005, the International VLBI Service for Geodesy and Astrometry (IVS) examined current and future requirements for geodetic VLBI, including all components from antennas to analysis. IVS Working Group 3 “VLBI 2010”, which was tasked with this effort, concluded with recommendations for a new generation of VLBI systems. These recommendations were based on the goals of achieving 1 mm measurement accuracy on global baselines, performing continuous measurements for time series of station positions and Earth orientation parameters, and reaching a turnaround time from measurement to initial geodetic results of less than 24 h. To realize these recommendations and goals, along with the need for low cost of construction and operation, requires a complete examination of all aspects of geodetic VLBI including equipment, processes, and observational strategies. Hence, in October 2005, the IVS VLBI2010 Committee (V2C) commenced work on defining the VLBI2010 system specifications. In this paper we give a summary of the recent progress of the VLBI2010 project

INTERNATIONAL LOW-FREQUENCY VERY-LONG-BASELINE INTERFEROMETRY NETWORK PROJECT MILESTONES

The low-frequency very-long-baseline interferometry network (LFVN) project was started in 1996, having the purpose to arrange the international very-long-baseline interferometry (VLBI) cooperation with participation of former Soviet Union radio telescopes. Currently there are three directions of LFVN development: a Mk 2 subsystem at 92 cm wavelength for solar research, an international S2 ad hoc array at 18 cm for active Galactic nuclei and OH-maser survey, and VLBI radar at 6 cm for investigation of Solar System bodies. 14 VLBI experiments were carried out using various combinations of radio telescopes in Canada, China, England, India, Italy, Japan, Latvia, Poland, Russia, South Africa, Ukraine and USA. The five sessions were processed by the Jet Propulsion Laboratory (California Institute of Technology) Block II and Dominion Radio Astrophysics Laboratory Penticton correlators. The Russian Mk 2 correlator in Nizhny Novgorod is under development. The paper describes the main project milestones, results ob...

The DBBC environment for millimeter radioastronomy

The Digital Base Band Converter project developed in the last decade produced a general architecture and a class of boards, firmware and software, giving the possibility to build a general purpose back-end system for VLBI or single-dish observational activities. Such approach suggests the realization of a digital radio system, i.e. a receiver with conversion not realized with analogue techniques, maintaining only amplification stages in the analogue domain. This solution can be applied until a maximum around 16 GHz, the present limit for the instantaneous input band in the latest version of the DBBC project, while in the millimeter frequency range this maximum limit of 0.5-2 GHz of the previous versions allows the intermediate frequency to be processed in the digital domain. A description of the elements developed in the DBBC project is presented, with their use in different environments. The architecture is composed of a PC controlled mainframe, and of different modules that can be combined in a very flexible way in order to realize different instruments. The instrument can be expanded or retrofitted to meet increasing observational demands. Available modules include ADC converters, processing boards, physical interfaces (VSI and 10G Ethernet). Several applications have already been implemented and used in radioastronomic observations: a DDC (Direct Digital Conversion) for VLBI observations, a Polyphase Digital Filter Bank, and a Multiband Scansion Spectrometer. Other applications are currently studied for additional functionalities like a spectropolarimeter, a linear-to-circular polarization converter, a RFI-mitigation tool, and a phase-reference holographic tool-kit.

VLBI at APEX: First Fringes

We have equipped the APEX telescope for 1 mm VLBI and obtained first fringes on 3C 279 at 229 GHz in May 2012 with SMA (Hawaii) and SMTO (Arizona). The fringe spacing achieved was 29 microarcseconds, adequate to directly observe strong-field general-relativistic effects around the black hole in the Galactic center by resolving the expected diameter of the shadow of the event horizon in Sgr A* of ∼ 40 microarseconds. I present on behalf of the collaboration the unusual aspects of this high-altitude VLBI installation, and the prospects for upcoming observations with a global array at the highest resolution.