[evlatests] ea04 pointing oscillations

[Rick Perley]

     In my science run from last Friday, one antenna -- ea04 -- is 
showing periodic gain oscillations.  This is an 'old ACU' antenna.  The 
oscillations are almost certainly due to pointing. The period is 6 
seconds, and the amplitude indicates cyclic pointing errors of a few 
tens of arcseconds.  It was doing this for all the observations of the 
target source and its nearby calibrator (so, azimuths running from 135 
to 200 degrees, and elevations from 52 to 59 degrees), but not on the 
flux calibrator 3C286 (observed at a lower (82) and higher (245) azimuth.

     I attach a gain plot (so that high values are from off-source 
positions, and the lowest values are when the antenna is on source).  
This is from the flagged data, so the high 'spike' indicates data that 
was not, but should have been, flagged.  The 6-second oscillations are 
seen in all raster points (even when on-source), but are much more 
obvious when the source is on the side of the antenna beam.

     Rick


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