  The VLBI technique can image compact radio sources with resolutions of the
order of the milliarcsecond and can determine astrometrically relative
positions with submilliarcsecond precisions. We determined the angular
separations among the radio sources in the triangle 1803+784/1928+738/2007+777
with submilliarcsecond accuracy from a weighted least squares analysis of the
differential phases. The comparison of the estimated separation of the pair
1928+738/2007+777 with previous such estimates obtained from data at different
epochs allowed us to align the maps of 1928+738 at diferent epochs relative to
those of 2007+777, showing that the jet components of 1928+738 display proper
motions, and suggesting an identification for the position of the core of this
radio source. We have also observed astrometrically the complete S5 polar cap
sample, that among the 13 sources within 20 degrees to the celestial North Pole
includes the above 3. These observations are carried out in the framework of a
long-term astrometric program to determine the absolute kinematics of radio
sources in the S5 complete sample.
