[evlatests] One phenomenon explained ...

[Rick Perley]

An addendum to the previous post:

In examining the DFTIM 'waterfall' plots carefully, I think I can 
explain the apparent 'bad data' for the moon for the 'speedy' antennas.

I notice that the reflected circularly polarized signal is visible, at 
the normal strength, for the 40 seconds of data preceding the apparent 
arrival of the 16 new ACU antennas.  For these 40 seconds, only the 
'speedy' antennas are claimed to be on source.  What I thought was 
evidence of bad data for these 40 seconds -- easily visible at the 
bottom of the attached screenshot, is actually just higher noise, as 
there were only nine antennas on source at the time.

The attached screenshot shows just the first scan -- this is the V 
vector sum, with frequency on the horizontal axis, time on the 
vertical.  The bright circularly polarized reflection is easily seen 
throughout.  The bottom 40 seconds shows notable noisier residuals -- 
which I originally thought represented bad data, but which is now 
interpreted to be just the higher noise due to the reduced number of 
antennas contributing to the vector sum. The evidence is the continuance 
of the V signal.  For the (flagged, therefore not visible) data prior to 
the bottom row, this V signal is not present.

The sudden transition to better data is easily seen, 40 seconds up from 
the bottom row, and is caused by the amazingly simultaneous arrival of 
all the other antennas (or, perhaps more likely, the on-line flagging 
deciding this was a good time to declare things normal).

So I think the only 'mystery' is how 16 'new ACU' antennas can arrive at 
the target source, after so long a journey (nearly 180 degrees of 
azimuth rotation) at exactly the same time.

Rick
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