BEAM_STEP

      BEAM_STEP   Integer

    Number of channels per synthesized beam plane.

    Default is 0, meaning only 1 beam plane for all channels.  N (>0)  indicates
    N consecutive channels will share the same dirty beam.

    A  value  of -1 can be used to compute the number of channels per beam plane
    that ensures that the angular scale does not deviate more than a fraction of
    the map cell at the map  edge.  This  fraction  is  controlled  by  variable
    MAP_PRECIS (default 0.1)