[daip] Re: AIPS question

[Eric Greisen]

Tracy Clarke writes:

 > We are working on GMRT data in India and have run into an odd issue we
 > wanted
 > to ask you about. We are working in 31DEC05 AIPS and the way the GMRT
 > writes their data they have two sidebands, one with a negative frequency
 > increment and one with a positive. They allocate this increment by writing
 > the
 > sideband label in the FQ table as -1 for the file with the negative
 > increment
 > and +1 for the sideband with the positive increment. We have noticed in
 > IMAGR
 > though that this does not work in 31 DEC05 and so IMAGR thinks both data
 > sets
 > have positive increments. I did a quick fix to this by re-writing the
 > channel width in
 > the FQ table to be a negative channel width and so IMAGR now calculates
> things

    Yes - the sideband code is not used so far as I know and the
channel width has been handled badly until recently (i.e 31DEC06) when
the 2 differ.  IMAGR may well get it right but DBCON and SPLAT with
averaging of channels did not.  This is the correct fix and is an
error on the GMRT's part.

 > for the correct frequency. I am worried though about CALIB. It is not clear
 > to me
 > what this will mean for CALIB and I have spent the day trying
 > (unsuccessfully) to
 > do tests to see if CALIB is calculating the channels with the correct
 > negative
 > frequency increment or if it is seeing a positive one. Could you please
 > advise me on
 > how to determine what exactly CALIB is seeing for the frequency increment?

Why do you think CALIB cares?  It is a continuum task.

Eric Greisen