[daip] [!11045]: AIPS - BB379 - amplitudes very low on EB

[Michael Bietenholz]

Michael Bietenholz updated #11045
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BB379 - amplitudes very low on EB
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           Ticket ID: 11045
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/11045
                Name: Michael Bietenholz
       Email address: mbieten at yorku.ca
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 25 September 2017 06:14 PM
             Updated: 25 September 2017 06:14 PM
           Reply due: 27 September 2017 06:14 PM (2d 0h 0m)
      Resolution due: 21 June 2020 12:00 AM (999d 5h 46m)

HiI'm looking at the data for BB379A (X-band VLBA+EB).  There were no EB Tsys values in the TY table, so I got them from http://www.vlba.nrao.edu/astro/VOBS/astronomy/may17/bb379a.  EB Tsys looked fine (30-60K);  CL-table gains produced by APCAL also looked reasonable (~7 or so ro EB, 20~30 for VLBA antennas).However, when I apply these gains, the visibility amplitudes for EB are very low - see attached UVPLT amp-vs-uvdistance screenshots, which have EB values in red and others on yellow.  The two plots are for two of the calsources - you can see EB is very low on both.  The data were averaged somewhat in freq (16 channels) and time (20secs) to make those plots but I checked the full resolution data and they show the same pattern so it's not due to averaging over some phase-winds.  I also attach a POSSM plot of a minute worth of data during the first 3C345 scan with various baselines to LA (chosen as refant), without any calibration applied.  EB has low amps (although partly expected due to its higher gain),  and for EB both amps and phases are quite variable across IFs, unlike for the VLBA antennas.Do you guys have any idea what might have gone wrong here?

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