[evlatests] SY table values

[Michael Rupen]

In Rick's test, the correlator receives new configurations as follows:

X -> L: configuration change
L -> S -> Clo -> Chi: no configuration change
Chi -> X: configuration change

So as expected the only correlator configuration changes are those
corresponding to sideband changes (i.e., to/from X band), where
Rick sees the largest discrepancies.

           Michael

>    Bill Cotton modified the 'BDF2AIPS' program to prevent SY table
> values being recorded when there are no valid visibility data.  This is
> very effective in removing nearly all (and perhaps all) of the
> outrageous PSum and PDif values which so cluttered the editing process
> associated with reviewing these tables, prior to their application.
>
>    Perusal of the SY table values in the original database (the one
> filled without Bill's update) shows the nature of the problem:
>
>    I looked at a sequence of observations that changed the band in the
> following sequence:  L -> X -> CLo -> CHi -> S -> L, noting changes in
> the values of PDif and PSum at each of the transitions points.  Note
> that the SY table is recorded at 1-second intervals, while the
> visibility data were averaged in the CBE to 5 seconds.  This difference
> may be important.
>
>    A) From L to X:  The SY table for the L-band data showed no change
> after the last valid visibility record.  Indeed, the SY table values
> continued on for 11 seconds past the actual end of the scan.  The
> following X-band file contains 8  records (1 second each) preceding the
> first valid visibility data, the first of which is  greatly discrepant
> form the following values.  The other 7 values show a smooth transition
> in PSum, presumably associated with subreflector rotation, and no change
> in PDif.
>    B)  From X to C-Lo.  There are two SY table records following the
> last X-band visibility record, and both are outrageous by any criterion
> -- with PSum and PDif 10 to 100 times too high.  There are about 12 SY
> table entries in the C-Lo band file which precede the first valid
> visibility record, the first two of which are greatly discrepant, and
> the rest showing some sort of smooth change, but with a 'jump' to a new
> value at the same time as the first valid visibility.
>    C) From C-Lo to C-Hi.  No change in sideband is expected here.
> There are about 4 records in the SY table of C-Lo beyond the end of the
> scan, but no abrupt change in either PDif or PSum.  The C-Hi database
> has two records preceding the first valid visibility -- these are not
> extreme, although clearly incorrect.
>    D)  From C-Hi to S.  There are two SY records in C-Hi after the end
> of the visibility data, the last of which easily qualifies as
> 'outrageous', with a values of Psum about 1% of the correct value.  The
> S-band dataset (curiously!) shows no SY data in advance of the first
> visibility.  However, the first eight values are clearly very incorrect
> -- a factor of up to ten wrong.  These were not removed by Bill's
> updated filler, as the visibilites were non-zero-integer.  However,
> these visibilities are clearly wrong, and were flagged out by the
> on-line system.
>    E)  From S to L:  SY tables values in the S band database were
> present 2 seconds past the end of the visibilities, but only the last
> one of these was unusual, and only by a small value.  There were only
> two SY tables values in the L-band database in advance of visibility
> data, the first of which was very discrepant in PSum.
>
>    Summary:  The largest discrepancies accompany change of subband.
> But all frequency changes are accompanied by erroneous values in the SY
> tables.
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