[evlatests] VLA image -- and an interesting clue ...

[Barry G. Clark]

This is all very strange.  Can this be duplicated in CASA?
I suppose it is possible, though extremely unlikely, that
something could be going wrong with the application of delay
and bandpass corrections as channels are added together.  We
are running short of straws to grasp at here.

>     I calibrated the VLA data, taken simultaneously with the WIDAR
> test
> data.
>
>     The images are very nice, with loads of the expected background
> sources.
>
>     I then returned to the WIDAR images, specifically the set of
> 'noise'
> images (blank field).  There are three, made with 1, 10, and 100 MHz
> BW
> each.
>
>     The peak background source in the 1 MHz wide field is 11.2 mJy
>     The same object in the 10 MHz field is now only 7.1 mJy
>     The same object in the 100 MHz field is now essentially invisible,
> at 1.2 mJy!
>
>     The VLA dataset shows this background source at 17  mJy.
>
>     For the VLA correlator dataset and the WIDAR 100 MHz dataset, the
> expected thermal noise limits should be about the same  -- and they
> are,
> at 0.15 mJy.
>
>     From this, I'm guessing that the act of coherently summing over
> the
> bandpass is actually destroying the signal (but not the noise).
> Something is backwards?
>
>
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