SPWINDOW

    [ALMA\] SPWINDOW ispw width frequency [/BASEBAND i]
            [/POLAR p] [USE u] [/RESET]

    This  command  is used to define a spectral window in the i-th baseband.
    The /BASEBAND option is mandatory, unless a a PLOT BASEBAND command  has
    been run, in which case the plotted baseband is selected.

    The parameters of the spectral window are then defined as follows:
      - 'ispw' is the correlator window number (each baseband has its
        own list) -- Currently, it can only be equal to 1 (one spectral
        window per baseband).
      - 'width' is the bandwidth in MHz: 31.25, 62.5, 125, 250, 500,
        1000, or 2000. NB: for simplicity, the software accepts and
        corrects 32, 60, 64, 120, 128, 256.
      - 'frequency' is the center frequency (in MHz) of the window in the IF
        domain, as displayed in the plot produced by PLOT BASE.
      - The /POLAR option is used to define how many polarization products
        must be computed (1,2, or 4). Default is 1.
      - The /USE option defines which fraction of the correlator is to
        be used. This modifies the number of output channels, and therefore
        the spectral resolution. Default is 100. Valid values are 3.125%,
        6.25%, 12.5%, 25%, 50%, and 100%. Entries < 1 are accepted (e.g. 0.5
        instead of 50).
    Depending on all these input parameters, the software checks whether one
    or several correlator modes are available (not all combinations are pos-
    sible).  Obvioulsy, defining several windows on one baseband is possible
    only if each window uses < 100% of the correlator resources.

    The command "SPWINDOW ispw" with no additional parameters calls  an  in-
    teractive mode in which the spectral window can be defined with the cur-
    sor:
      - Left hand click defines the central frequency.
      - +/- increases/decreases the bandwidth
      - < and > shifts the position of the unit by 5 MHz
      - P changes the number of polarization products (1-2-4)
      - U and I decrease/increase the fraction of the correlator to
        be used for that spectral window.
      - E is used to Exit this mode
    The plot is updated after each action.