The way mm-VLBI works is that telescopes across the world which can
operate at high frequencies (short wavelengths) are combined. The
signal of each mm-telescope is recorded on a tape which is later
shipped to a central location - the correlator - where the tapes are
played back. The recorded waves interfere with each other in the
correlator and from the interference pattern one can reconstruct the
structure of the observed source. This sounds complicated, and indeed
it is. The huge benefit of this technique is that the combined
telescopes have the resolution of one single antenna the size of the
earth. The map below shows a number of mm-telescope sites in the world
(with the "European" antennas in red and "American" antennas in
black).
(Figure: Millimeter-telescopes which participate in mm-VLBI observations, e.g. of the Galactic Center)
