[daip] RE FRING problem.

[Craig Walker]

I have some new evidence on the fring problem that I reported last
week.  Amy said that the problem had something to do with confusion
between 4 and 8 IF's - there are really 4 but in some buffer operations, 
FRING is acting like there are 8.

The file came out of the correlator thinking it had 8 
single-polarization IFs.  I ran FXPOL on it, changing it to 4 dual 
polarization IFs.

LISTR 'SCAN' listing indicates 8 under source information and 4 under 
frequency table information.

Later I ran CLCOR to move the phase center to the northwest lobe of 
Cygnus A.  That made the fringe rates on the detected baseline worse.
So I wanted to run CLCOR to go to the southeast lobe.  But by now the SU 
table had the northwest lobe position.  Putting in opposite shifts did 
not have quite the right effect (3 mas difference), presumably because 
the declincations used in the cos(dec) calculations for RA were 
different in the two cases (something to think about).  Anyway, in the 
end, I deleted the SU table and copied one from another file that was on 
disk from the same observations.  But I just now determined that that 
file had not been through FXPOL.  So the copied SU table thinks that 
there are 8 IFs.  That probably explains the source of the confusion 
about the number of IFs.

Given CLCOR's behavior, it is not too unlikely that other people will be 
copying SU tables around.  So I suggest that FRING (other programs?) 
keep an eye out for such inconsistencies.

Meanwhile, I am messing with my disks, including taking the one with the
offending file home.  I tried to make an identical copy of the data set 
on my disk 1 with UVCOP.  But UVCOP is not like unix cp.  It fixed the 
SU table.  So the problem did not recur.  So I deleted the SU table and 
copied the one from the offending file on disk 6.  Indeed, now FRING 
misbehaves (rates of E-20).  So you can now test the problem with the 
file on eolus disk 1 user 262 catno 4.

Cheers,

Craig



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     R. Craig Walker            Array Operations Center
     cwalker at nrao.edu           National Radio Astronomy Observatory
     Phone  505 835 7247        P. O. Box O
     Fax    505 835 7027        Socorro NM 87801   USA
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