BASEBAND

    [ALMA\] BASEBAND i frequency [sideband]

    The  ALMA  correlator  is composed of four quadrants, each of them being
    able to process 2 GHz (x 2 polarization) of the receiver output. This is
    called a baseband, and this 2 GHz slice can be placed at any position in
    the receiver bandwidth. The BASEBAND command is used to define the  i-th
    baseband, by selecting the frequency of its center. This can be done ei-
    ther in the RF or the IF domains
      - if the frequency is < 1000, it is interpreted as a rest frequency
        in GHz.
      - if the frequency is > 4000, it is interprested as an intermediate
        frequency in MHz; a second parameter giving the sideband (LSB/USB)
        is then necessary.

    Example: Receiver band 7 is tuned at 220 GHz LSB (with command
    FREQUENCY). It outputs 4-8 GHz
    signals in USB (corresponding to 234 to 238 GHz) and LSB (218 to 222
    GHz). Baseband 1 can e.g. be placed at IF = 6.2 GHz in LSB, which
    corresponds to 220.8 GHz. The commands "BASEBAND 1 220.8" and
    "BASEBAND 1 6200 LSB" are therefore equivalent.

    Entering "BASEBAND i" with no further arguments calls an interactive
    mode in which the baseband is defined with the cursor on the plot
    produced by the FREQUENCY command. Clicking in the plot defines the
    frequency/sideband of the center of the baseband. Basebands are
    automatically shifted to be fully included within the IF band.

    The command "BASEBAND" alone enters a loop to interatively
    define all four basebands (it is equivalent to FOR I 1 TO 4;
    BASE I; NEXT).