Up: PDBI and ALMA languages
[PDBI\]SPECTRAL iunit bandwidth fcent /NARROW 1|2 [/BAND LSB|USB|DSB]
Select the width and position of each spectral unit of the narrow-band
- '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
- Left hand click defines the central freuency and the narrow band
- +/- 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|DSB can be used to define the processing mode of
the selected correlator unit. There is no practical difference between
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 channels
suffer from the Gibbs effect. This mode is therefore not optimized for
spectroscopic studies. Choosing between an SSB or DSB mode is possible
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). De-
fault 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.