[evlatests] Problems with referenced pointing?

[Rick Perley]

     I had a long X-band observation in the evening of August 11.  As 
the target source is large (2 arcminutes), I ran referenced pointing 
hourly, at X-band, using a very nearby calibrator (J2007+4029) -- very 
strong (2.5 Jy), very clean.

     The results are bizarre.  Attached is a voltage gain plot for ea13 
-- most other antennas show similar results.  The two plots are for RCP 
and LCP.

     Large steps in gain are seen, all of them coincident with the 
referenced pointing times.  I observed the calibrator before and after 
the referenced pointing -- and the steps coincide in every case.  The 
largest step is a 6% change in amplitude -- 12% in power.  That's ~ 1 
arcminute change in position at 10 GHz.

     Did the antennas really do this?  The referenced pointing data say 
no.  For the large step at 05:30 IAT, the change in antenna position, as 
given in the referenced pointing data, was a mere 6 arcseconds.

     The weather was relatively benign -- 5 m/s typical wind.  The 
elevation was quite high -- nearly 80 degrees.  However, the other steps 
seen earlier are all at moderate elevation.  It should be noted that the 
jumps are upwards at 3:30 and 4:30 IAT -- this means the application of 
the solutions *worsened* the antenna positioning.

     Something is not right here.
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