[evlatests] ea01 tilt mystery

[Ken Sowinski]

There has been a mysterious change in tilt for ea01 this month.
I document what is known in the hope that someone can explain
what is happening.  the evidence points to something happening
to the antenna on November 4.  Most likely it is unrelated to
the subreflector because it is expressed as a change in tilt,
rather than collimations.  Does anyone remember any work done
to ea01 on that day that can affect its tilt by more than an 
arc-minute?

Chronolgy:
Sep 17  ea01 was moved from W16 to W09.  A tilt error was measured
         and applied to the pad.
Sep 23  Another pointing run confirmed and refined the previous tilt
         measurement.

Several pointing runs from Sep 23 to early morning Nov 04 confirmed
correct pointing terms, including tilt, for ea01.

Nov 11  A large tilt error was noticed for ea01 during a collimation
         run.  Collimation errors were small at all bands.
Nov 27  An X band pointing run confirmed tilt errors for ea01.

Additional Information
>From weekly focus checks, is is clear that the high frequency
performance of the antenna deteriorated between Nov 04 and Nov 12.
Examination of pointing results in November suggest that ea01
got worse between Nov 03 and the end of the day on Nov 04.  Nov 04
was a maintenance day.

The tilts for W09 and EA01 in the parameters database have not 
changed, nor has the PADAZ term for W09.