[evlatests] More amazing phenomenology ...

[Ken Sowinski]

On Tue, 14 Jul 2009, Rick Perley wrote:

>    It looks like a slow slippage in phase tracking, which starts at
> zero at the observation's beginning.  Antenna 25 is at N2, while antenna
> 28 is at N8.

The problem with these two antennas is that the data coming out
of the correlator is mislabelled.  Baselines involving ea25 are
reported as from ea28 and vice versa because the station board
station numbers have been misset.  Downstream this can lead to
confusion when u and v are associated with the visibilities.
The delay polynomials are correctly getting to the expected
station boards

This had to have happened only recently so cannot explain all the
problems we have seen, but does explain the recent reports from
Ed, Rick and George about ea25 and ea28 being "different".

The change can be pinned down to having occurred between July 2
and July 8.  On July 2 Michael and I played the game of observing
while breaking one antenna at a time to verify that visibilities
in AIPS are associated with the right antennas; we found no problems
but maybe that data should be reviewed just in case.  On July 8
Kerry wrote describing which station boards were working and listed
ea25 and ea28 in rack 2 wrongly ordered.  On July 9 I observed the
same wrong order in station IDs, but did not realize at the time
that it was wrong.

In summary, the station IDs in those two station boards were probably
wrongly set between July 6 and July 8.  Mapping problems after that
time can be explained by this if the image improves when those two
antennas are flagged.  Mapping problems before that must have other
causes.