Up: PDBI and ALMA languages
[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
- 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).