[evlatests] Beam Cuts for ea21 -- notable issue with Horizontal Motion

[Rick Perley]

    We are attempting to characterize the behavior of the antenna motion 
on ea21, prior to its move later this week to the barn for the ACU retrofit.

    To do this, we made four 'holographic' cuts through the main beam, 
along the azimuth and elevation direction.  This was done at L and X 
bands.    A 0.1 second integration was used (to search for rapid 
oscillations), and 10 seconds per pointing.  Each cut is 11 points long, 
and the oversampling is 5X -- essentially we're cutting through the main 
lobe only. 

    Attached are two plots for X-band, for baseline 17 x 21.  Note that 
for the vertical cut, the steps are crisp and rectangular, beyond ~1 
second settling.  However, for the horizontal cut, something else is 
going on, and even after ~10 seconds, there is no clear sense that the 
antenna has stabilized.  This behavior is not unique to 21 -- others 
show the same thing.  The same behavior is seen at L-band, although the 
amplitude excursion is much smaller (as expected). 

    We plan to do 20-second pointings next (to see how long it takes to 
really settled), and to do cuts at K-band, for which the deviations 
should be much larger. 
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