[evlatests] WIDAR baselines, and time offsets

[Rick Perley]

    1)  My error on the 'conjugation'.   Both real and imaginaries have 
their signs reversed to get an apparent 180 rotation. 

    2) It's 33 seconds, not 32.  The VLA data have a 1.67 second 
granularity, the WIDAR data are at 1.0 seconds. 

Bryan Butler wrote:
>
>
> 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...