[evlatests] More odditites

[Rick Perley]

    Closer inspection of the data taken this morning has shown some 
other effects worthy of note:

    1) Antenna 19's phase on IFs B and C has two states, separated by 
about 120 degrees.  The states change every 5 seconds, with B and C 
exactly out of phase.  (i.e. -- when B's phase drops, C's phase rises).  
The change in state is nearly instantaneous.  IF 'A' does not show this 
effect.  IF 'D' was flagged out due to the correlator problem. 

    2) All the EVLA antennas' amplitudes are fluctuating up and down on 
a very rapid timescale, between two different amplitude states, 
separated by about 2%. 

    3) There are strong phase winds (more than 10 degrees/minute) on 
some antennas (both EVLA and VLA), notable especially at L-band on 
antennas 17, 22, and 24 -- all of which I see are at the end of the West 
arm.  Could perhaps be ionospheric in origin -- we'll need another test 
to be sure. 

    4) At X-band (and perhaps at others, I only checked X-band 
carefully), the detailed phase behavior is very odd.  For example, 
antenna 23 has a 20-degree parabolic phase shape, repeating once every 
10 seconds.  (In other words, a plot of phase vs. time shows a series of 
little parabolas, oriented with the focus down, with amplitude of 20 
degrees and a period of exactly ten seconds).  Upon closer review, we 
see similar patterns for the *EVLA* antennas whose positions are near 
the ends of the arms.  Antennas 17, 18, 21, and 23 are especially 
notable here.  These are at W64, E72, N64, and E56, respectively.  The 
inner EVLA antennas do not show this effect.  The IFs have all their 
parabolas oriented identically, for any given antenna. 

    All of the above, under 'Modcomp control'.