[daip] problems with RLDLY

[Eric Greisen]

Lister, Matthew L wrote:
> I see that in the new version of AIPS CRSFRING has been replaced with RLDLY. I am not able to get this
> task to correct the phases across the IFs in BL149CZ. The task corrects the slope within the IF, but does not
> correct for the phase offsets _between_ IFs.  This is a VLBA dataset with identical parameters to previous BL149 
> segments that have been reduced successfully with CRSFRING.  
> 
> Plots can be found at
> http://www.physics.purdue.edu/~mlister/LLPLOT.PS
> http://www.physics.purdue.edu/~mlister/LRPLOT.PS
> http://www.physics.purdue.edu/~mlister/LRPLOT_PRE_RLDLY.PS
> The first is the parallel hand POSSM plot pre RLDLY, and the 2nd is the cross hand plot post-RLDLY, 3rd is
> the cross hand before RLDLY was run. 

The presumption I had about this was the following.  If you are going to 
image cross-hands, then you will need to run PCAL and RLDIF.  The latter 
corrects for the R-L phase difference.  Note that RL and LR are not 
supposed to have 0 phase but instead to have a phase related to the 
source polarization - something unknown to RLDLY or CRSFRING for that 
matter.  Note also that CRSFRING remains available although it is a real 
kludge of a procedure.

Eric Greisen