[evlatests] One phenomenon explained ...

[Rick Perley]

Doug:

Thanks for this — very good to know.  
Ea06 and 10 act like the ‘old’ systems.  Are we sure they have, in fact, new ACUs?

Rick

Sent from my iPad

> On Nov 15, 2023, at 7:04 PM, Doug Whiton via evlatests <evlatests at listmgr.nrao.edu> wrote:
> 
> Rick,
> We should expect the antennas with new ACUs to move with precision (within
> several milliseconds).  The biggest mystery for me is why 6 and 10 were
> not behaving as expected.  I'm sure Bruce will want to look into that.  We
> are aware of the fact that the old ACU antennas are running on upper edges
> of the slew speed spec and setting their slew speed is far from precise.
> 
> Doug
> 
> 
>> 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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> 
> -- 
> Doug Whiton
> Hancock VLBA
> National Radio Astronomy Observatory
> 603-525-4332
> 
> 
> 
> 
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