[evlatests] WIDAR baselines, and time offsets

[Bryan Butler]

Ken Sowinski wrote, On 7/7/09 10:07:
> 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

agreed.  it's the sign of the phase, not the sign of the imaginary part, 
that's at issue (and is what the "sign convention" here refers to).  i'm 
wondering how the CBE could get that sign wrong...

> 
>>    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.
> 

in fact, one would expect it to be 34 sec currently, since that's what 
the current dAT (leap seconds) is.  does this mean we've got a lurking 
definition of what the leap seconds are somewhere in the software that 
hasn't been updated in 2 years?  it'd be nice to know if this really is 
exactly 32 seconds instead of 34...