SPECTRAL
Keywords: astro

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SPECTRAL

        [PDBI\]SPECTRAL   iunit   bandwidth    fcent    /NARROW    1|2    [/BAND
        LSB|USB|SSB|DSB]

        Select  the  width and position of each spectral unit of the narrow-band
        correlator.
          - 'iunit' is the correlator unit number (1 to 8)
          - 'bandwidth' is the bandwidth in MHz (20, 40, 80, 160, or 320)
          - 'fcent' is the center frequency (in MHz) of the unit in the
             third IF, i.e. the IF at the entry of the narrow-band correlator
             (in the range 100 to 1100 MHz).
        The option /NARROW is mandatory, and is used to select  which  entry  of
        the  correlator  the  unit is connected to. The SPECTRAL command updates
        the current plot by drawing the position and width of the selected  cor-
        relator  unit.  The  list of the current correlator setup, including the
        number of channels and resolution, is printed out.

        Alternatively, the command "SPECTRAL  iunit"  with  no  other  arguments
        calls  the  cursor  and  allows one to define interactively the spectral
        unit:
          - Left hand click defines the central freuency and the narrow band
            unit
          - +/- increases/decreases the bandwidth
          - < and > shifts the position of the unit by 5 MHz
          - E is used to Exit this mode
        The plot is updated after each action.

        Option /BAND LSB|USB|SSB|DSB can be used to define the  processing  mode
        of  the  selected  correlator unit. There is no practical difference be-
        tween LSB and USB tunings. The DSB mode provides twice as many  channels
        than  the LSB or USB modes for the same bandwidth, but the central chan-
        nels suffer from the Gibbs effect. This mode is therefore not  optimized
        for spectroscopic studies. Choosing between an SSB or DSB mode is possi-
        ble only if a bandwidth of 160 or 80 MHz has been selected (320  MHz  is
        only  available  in  DSB mode; 40 and 20 MHz are only available in SSB).
        Default is DSB for 320 MHz wide units, LSB for the other bandwidth.  The
        /BAND  option has no consequences on the plot produced by ASTRO, but af-
        fects the printout (number of channels and  resolution)  and  the  setup
        file produced by the PRINT command.