[daip] Possible problem with FRING

[Lincoln Greenhill]

Hi Amy,

We run FRING twice, once for obtain a manual phase cal and once to obtain
a multi-band solution.  We rely on the first run to remove difference in
slope (phs vs freq) from band to band.  I do not know what the POSSM
plots show for any particular CL table in this case, but I wanted you to
know that our plan is not different from the S.O.P. for the VLBA.

I'll leave the specifics to Alice w/r to whether there are anomalies
in this particular processing.

> phase cals.  Also if you want to apply a multi-band delay after
> that then APARM(5)=1 should probably be used since that will
> put the multi-band delay in the part of the SN table that
> will be applied (the single band delay column, the multi-band
> delay column is never applied).  In other words, if you use
> APARM(5)=2 you never actually apply a multi-band delay.  So
> our main question is why you use APARM(5)=2?

We normally use APARM(5)=2 because historically, it seemed to give us
better results, i.e., better solutions (less scatter). And past
documentation has supported the use of APARM(5)=2.  It is possible that
our thinking is swayed by our past close work with Haystack, for whose
software and definitions the multi-band delays are nonphysical in absolute
value.  For NRAO hardware/software, it seems to me that the possible slow
time variation in the phase offsets between the IFs will contaminate the
multi-band delay value but not the single band delay number.  This is
particularly important for dual polarization observing.

Regards,

Lincoln