[evlatests] Progress on WIDAR Imaging Woes

[George Moellenbrock]

Gang-

>    I believe that these characteristics are sufficient to explain all
> the imaging characteristics that we have seen, at all bands.

Bold claim!  See below re freq-dep effects....

> What has
> not yet been discovered is how this problem is generated.  George has
> confirmed that CASA sees the same effects.  He has already shown that by
> removing all data from these two antennas, the images are vastly
> improved, and background sources are properly showing up.

Yes, we have ruled out the path through UVFITS and the details
of Rick's processing (relative to mine) as potential culprits.

Also, returning to the 0217 + blank field dataset I reported on earlier,
I've found that excluding antennas 25 and 28 in the calibration and
imaging yields considerably better on-source images of 0217, i.e.,
the dynamic range for a 64 MHz bw continuum image is now
approaching 6000:1 (cf ~500:1?), and I begin to see some of the
background sources.  The blank field is imaging better, too, with
at least 1 additional weak source turning up more coherently than before
(and the one I reported on before is stronger).  (Note, however, that
this field remains limited by poor short timescale phase calibration.)

It is not yet clear that the frequency-dependent effects I noted
previously have entirely gone away....

-George