[evlatests] Subreflector motion errors

[Rick Perley]

     From the multi-band observation taken last Friday (17B-053), a 
small number of subreflector motion failures were found.  The failures 
were only at X and Ku bands (with one single exception). Both focus and 
rotation failures were noted.  The details are::

     1) The observations cycled through the bands in the following way 
for each source.  There were four sources.

          Ku -> K -> Ka -> Q -> X.

         For all, enough time was allocated to ensure the antennas were 
on source for all observations.

     2) Observations durations varied from 1 -- 2 minutes at X band to 
up to six minutes at Q.

     The failures noted were:

         a) at X-band:

                               * ea15 failed to rotate the subreflector 
to the correct position on three scans (out of 26). For one of these, 
the subreflector reached the correct position 1.5 minutes late.  This is 
not a case of a slow motion -- the phases clearly show the motion 
started 12 seconds before the subreflector reached the correct position.

                              * ea03 failed to change the focus on three 
scans (not the same as the ea15 failures) from the Q-band position.  For 
one of these, the subreflector did reach the correct focus point one 
minute after the scan began.  Again, this is not a case of a slow motion 
-- the phases clearly show the motion started six seconds before the 
correct position was reached.

                             * ea11 failed to rotate the subreflector on 
one scan (not the same as the preceding failures).

         b) at Ku-band:

                             * ea05, 10, 11 and 25 all failed to rotate 
the subreflector on one out of 26 scans.  The failures were all on 
different scans.

                              * ea05 also failed to change the focus 
position (from X-band) on two scans (neither the same as the preceding 
failures).  For one of these, the subreflector reached the correct 
position one minute late, and again, the phases show the motion started 
5 seconds prior to reaching the correction position.

         c) At Q-band:

                             * a single failure:  ea05 failed to rotate 
to the correct position.

     At K and Ka bands, no subreflector motion failures were found.

     A more exhaustive test (testing all band combinations) is probably 
warranted, and has been proposed.  Such a test would also test the 
recent changes made to ea10's T303.