Development of real-time VLBI and measurements of scintillation.

An accurate real-time VLBI system with 47 km baseline connected by a terrestrial microwave link is discussed. The theoretical aspects of the data reduction are addressed, including maximum-likelihood estimates of observables, cross-spectral function, cross-spectral function and fringe stopping, multilevel fringe stopping in the time domain, minimum redundant bandwidth synthesis, and sensitivity of delay time. Calculations of delay time and fringe rate are considered. The 4-GHz band system is described, including the antenna and receiver, frequency converter and frequency standard, formatter, microwave link, real-time correlator, time synchronization, and minicomputer and data acquisition software. Measurements of delay time, phase variation, phase scintillation, and visibility scintillation due to solar wind are discussed.