[evlatests] X-Band status, Modcomp-free, 26 June

[Rick Perley]

    After appropriate flagging was (manually) done on the observations 
referred to in the prior note, I find:

    1) Antennas 14, 19, and 21 are dead at all IFs.  It is noteworthy 
that none of these were flagged by the system. 
   
    2) Antenna 13A and 13B are very weak.  Antenna 13D is dead.   The 
amplitudes of all three 'working' channels are not behaving normally, 
with oscillations and 'clunks' occurring on many timescales. 

    3) Antenna 16C has three different levels, at 0.0, -1.6, and -3.8 dB 
in power.  There is a fairly clear periodicity in the pattern of drops 
-- 1.2 second period.   The 'zero' level defined above is itself below 
what would be considered normal, by about -3 dB. 

    4) Antenna 18A is fixed at a high (erroneous) level, with exactly 
180 degrees of phase on all baselines. 

    5) Antenna 16B has extremely unstable gains, varying by ~50% or 
more.    These are clearly related to large claimed changes in Tsys, 
seen in the tables. 

    6) Antenna 26 has three small 'short shallow drops' on IFs A and C 
only. 

    Overall, phases look pretty good, other than steady winds likely 
related to large baseline errors.  There are a multiplicity of small 
clunks and slopes, which I have come to understand are due to the VLA's 
phase and delay compensation system.  All of these are of 5 degree 
amplitude or less. 
    Some VLA antennas have steady phase winds.  For this observation, 
nearly all of these are on the west arm (6, 8, 4, 5, and 22).  The rate 
increases more or less with baseline length.  It is curious to me that 
this is not seen on the east arm, except for antenna 15.  In particular, 
antennas 3 and 20 (at E64 and E48, respectively) have nice steady 
phases.  It is possible we hit the stationary point (which happens once 
per day) by accident in this observation, but what's the probability ?   
Either that, or a fortuitous atmospheric wedge positioned itself just 
right ...  Similarly, all north arm phases are flat, except for minor 
slopes for antennas 7 and 26 (which are of opposite sign).