[daip] question about multi-freq data

[Eric Greisen]

Hiroko Shinnaga writes:

 >   I have a question about dealing with multi-frequency data.
 > I have a multi-freq (two frequencies) data in my disk.
 > 
 >    The cookbook says that each frequency must be calibrated
 > separately.   I'd like to know How I can calibrate them
 > separately.  Should I have to have two separate files for each
 > calibration?  Or one can calibrate those two frequency data
 > separately by setting the parameter "FREQID" of vlacalib
 > using just one CH0 file?
 >    The cookbook also says that when reading with such
 > multiple data, one can use fillm and set cparm(7)=-1.
 > However, since I had downloaded the data file via ftp, I didn't
 > need to use 'fillm'.  To deal with multi-frequency data,
 > is it necessary to use 'fillm' to create two files for each
 > frequency or can I just go ahead calibrate each frequency
 > using one CH0 file which includes both frequencies?
 > 

   When you say you have two frequencies, what exactly do you mean?

The traditional VLA data set has 2 IFs which are usually at two
similar but different frequencies.  The traditional VLBA data set has
several of these IFs.  If you mean FREQIDs, as shown by LISTR 'SCAN'
mode, then the easiest thing to do is to use UVCOP to write two data
sets each containing only one of the FRQIDs.  This simplifies the rest
of the reductions.

I worry a bit about your reference to CH0 file.  Is this a
spectral-line data set and are your separate FREQIDs actually very
close in frequency, differing only because of Earth rotation and minor
velocity offsets?  If so, then they should have been loaded as only
one FREQID and FILLM was run incorrectly by whoever ran FILLM for you.
It is essential for users asking the analysts to run FILLM so that
they may use ftp (rather than paying for tapes) to provide the
analysts with all necessary FILLM parameters.  They are not scientists
and do not know the contents of your experiment.

Eric Greisen