[evlatests] The Mystery of ea20's panels -- an hypothesis

[Rick Perley]

     The panels for ea20 were adjusted last March, using a K-band 
adjustment template.  Subsequent holography showed that although the 
surface had changed, there was no overall improvement.  So clearly, 
something went wrong.

     An attached figure (20-25-OLD-NEW-DIF.pdf) shows the effect. The 
top row shows the surface -- at Ku-band -- as it was in Dec 2014 (top 
left), and is now (top middle).  The difference is in the top right -- 
this in effect shows the changes made last March.

     The bottom row is a 'control' -- this is ea25, with the same 
sequence.  The difference map (lower right) shows essentially only 
noise, at a couple hundred microns.

     ( Note:  the left hand column has much higher resolution than the 
middle -- the resolution element is about half the size).

     The second attachment (2CHANGES.pdf) compares the template with the 
changes that have been measured:

     Top Panel:  The difference (at Ku-band) between the Dec 2014 and 
March 2017 holography runs.  This shows the changes that were actually 
implemented.

     Bottom Panel:  The template that was utilized to calculate the 
panel changes.  This shows the changes that were requested. (Data are 
from K-band, October 2011).

     The question is:  What transformation of the bottom panel results 
in the top panel?  The most obvious (to me) is that there is a 
reflection about the vertical axis -- changes meant for the left side 
were implemented on the right.  The comparison is not perfect, but is 
pretty good.

     Another possibility is a rotation by 90 degrees.

     The proposed panel displacement test should be definitive.

     Rick

-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2CHANGES.pdf
Type: application/pdf
Size: 93638 bytes
Desc: not available
URL: <http://listmgr.nrao.edu/pipermail/evlatests/attachments/20170317/29abe9b1/attachment-0002.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20-25-OLD-NEW-DIF.pdf
Type: application/pdf
Size: 151013 bytes
Desc: not available
URL: <http://listmgr.nrao.edu/pipermail/evlatests/attachments/20170317/29abe9b1/attachment-0003.pdf>