Interferometric Observations with a Baseline of 127 Kilometres--I

Abstract

This is the first of two papers describing observations made on 46 radio sources smaller than one second of arc with a long baseline interferometer using a radio link. The frequencies used were 1422 MHz, 2694 MHz, and 4998 MHz, giving baseline lengths of $$0.6 \times 10^{6} \lambda, 1.1 \times 10^{6} \lambda \,\text{and} 2.1 \times 10^{6} \lambda$$ respectively. Twenty-three of the sources were observed fully at one or more of the three observing frequencies. In this paper the normalization and calibration procedures are described and the results are given on those sources whose fringe visibilities showed no significant variation with hour angle. Upper limits to the angular diameters of these sources, or their unresolved components, have been calculated using a circular Gaussian model. Fringe visibilities are also given for the sources which were observed only briefly at either 1422 MHz or 2694 MHz.