[evlatests] VLA/EVLA phases (data from 10/05/06)

[Juan Uson]

Dear All,

I had 6 hours for holography at L and C bands on 60733 at 00:00:00  
LST.  I spent the first 77 minutes on 3C84 at X band in standard mode  
with dump times of 10 sec, 5 sec 3.33 sec and 1.67 sec to test the  
new controller.  All data were taken with the same correlator mode  
(standard continuum with 2 IF pairs and 50 MHz bandwidth).  I have  
not had a chance to look at the holography data yet.  I describe here  
only behavior seen in the on-source (calibration) scans on 3C84.

In order to clarify things, I first calibrated on a single scan at  
each frequency with sufficient flagging at beginning and end to have  
no end effects and using scan averages.  I applied this calibration  
to all the data so that anything that follows can be easily seen as  
departures of phases from zero and changes in amplitudes from unity.

I then removed all flags and re-calibrated using the respective dump  
times for solution interval, i.e. no time averaging whatsoever.  The  
usual beginning-of-scan problems are seen as well as an occasional  
end-of-scan.  Some phase jumps on EVLA antennas which occur on a time  
scale of less than one dump (i.e. less than 1.67 sec) and result in  
all EVLA antennas jumping in phase by the same amount (but different  
at each band) and are accompanied by a hiccup in the amplitude  
solution (showing that it is the EVLA that jumps, not the VLA).   
These jumps happen in the middle of a scan.

I also see some of the phase jumps in VLA antennas that Rick reports  
in his last note.  For example ~ 60 degrees for IF 2, antenna 3 when  
returning to L band after some time at C band.  Only a few antenna- 
IFs showed this.  However, I only changed bands, not correlator  
settings (as in Rick's tests).

In addition, the phase noise is too high (given the theoretical SNR)  
and not random (as seen in some of the plots, particularly in the R-L  
phase differences).
However, I only see this non-randomness clearly with dump times of  
3.33 sec and 1.67 sec (the only one used at L and C bands).  The last  
plot enclosed shows this at X band where the dump times were 10 sec,  
5 sec, 3.33 sec and 1.67 sec (the last two scans).

The enclosed plots show some of this behavior.  Some correspond to  
the full time, some show only one scan for clarity in showing trends.

Cheers,

Juan

Encl.:  PostScript plots:

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