[evlatests] Testing the 'subreflector rotation trick'

[Rick Perley]

    Ken and I tested Barry's implementation of the 'subreflector 
rotation trick'. 

    The following sequence of observations was set up, all at K-band:

    1) Regular observation of the source.
    2) Determine referenced pointing offsets.
    3) Observe source with offset pointing corrections applied.
    4) Determine referenced pointing offsets, with corrections applied 
(to check if they are really on).
    5) Observe source with offsets applied.
    6) Turn on the 'subreflector rotation trick' via an escaper command:
//  \subarray.setRotate(1)
       which followed the first source card that we wanted to try this 
on.  According to my understanding, this applies the 'trick' to this, 
and all subsequent cards (and not to any of the preceding cards). 
    7) Observe source with offsets, and rotation, applied.
    8) Determine referenced pointing offsets, with corrections 
determined from #2 applied.
    9) Observe source with offsets, and rotation, applied.

    Three difference sources were observed: 

    3C84, at elevation 82 degrees
    0423-013, at elevation 54 degrees
    0403-360, at elevation 20 degrees.

    Results:

    Cofirmation that the 'trick' is being correctly applied would be to 
see a distinct rise in correlated amplitude (especially for the low 
elevation source) between observations 5 and 7. 
    In fact, for no antenna, and for no source, was *any* change in 
amplitude seen between these scans.  Indeed, the only change in 
amplitude seen was between the observations 1 and 3 -- before and after 
the initial referenced pointing determination. 
    Thus, the data are consistent with no application of the 
subreflector rotation occurring. 

    Did I mis-type the escaper command?
    Does that command apply itself to all scans, independent of the 
location of the escaper?