[evlatests] Antennas 13 and 25

[Rick Perley]

    The curious amplitude 'square wave', of duration ~70 seconds, and 
amplitude 25%, which I reported as being seen on antenna 13, IF 'D' at 
L-band, is occurring at C and X bands also.  (I haven't checked K or Q 
yet).  In all cases, the effect is not seen in Tsys.  It cannot be due 
to any subreflector issue. 

    At X-band, I had two scans on the source, between which was a 
referenced pointing scan. 
    For the first scan, both antennas 13 and 25 gave very weak fringes 
-- barely discernible.  The data were flagged. 
    For the second scan, both antennas 'came to life' -- but with 
fringes only half the expected amplitudes.  The statistical weights were 
low by a factor of four -- as expected if (for example) if antenna was 
mispointed to the half power point. 
    The referenced pointing scan (in between) failed completely for 
antenna 25, and gave a large offset of many arcminutes for antenna 13.  
We are fairly sure that the subreflector is misbehaving on antenna 13.  
It may also be giving trouble for antenna 25.   

    Otherwise, C and X bands look quite good on all the other antennas.