Data obtained in November showed a significant dependence of the phase as a function of elevation, resulting in artefacts in the images. This effect is proportional to the frequency and was not significant at 3mm. It is caused by the non-intersection of the Azimuth and Elevation axes; a complete analysis of 22 sessions of baseline measurements carried on in 1995 and early 1996 allowed us to determine the most accurate values for this parameter: on antennas 2,3,4 respectively, antenna 1 being taken as the reference.
Since all projects have been affected, a command procedure has been set up to compensate the phase errors introduced by this effect. It has to be applied to the original data before performing the phase calibration.
Several temporary problems with the real-time calibration software are also automatically fixed by the same command procedure.