[evlatests] WIDAR baselines, and time offsets

[Ken Sowinski]

On Tue, 7 Jul 2009, Rick Perley wrote:

>    All coordinates have the same signs between the two arrays.   So,
> unless I am seriously misunderstanding something, it appears that we are
> inverting the signs of the visibilities (i.e., taking the complex
> conjugate).

conjugation does not, in general,  change the phase by 180 degrees

>    While making the comparisons noted above, I noticed that the two
> databases are not precisely identical in their time axes.  Michael R.
> noted some time delay between the arrays while the data were taken.  I
> can confirm this, based on the index files of the two (supposedly)
> parallel sets:  The VLA dataset is 32 seconds behind the WIDAR dataset.
> In other words, all scans in the VLA dataset start and stop 32 seconds
> later than those in the WIDAR dataset.

I would expect 33 seconds.  Data from the VLA correlator is
labelled in IAT, while data from Widar seems to be labelled
in UTC.  I hope that the sign of IAT-UTC is consistent with
what you describe.