[evlatests] EVLA Misbehavior Last Night

[Rick Perley]

    A 30 minute observation was taken last night at X-band, continuum 
mode, of ten calibrator sources.   Integration time of 1.67 seconds.

    Nine EVLA antennas were up and fringing, mostly quite well.  But ...

    1) Antenna 24 is seriously misbehaving.  The A and C IFs have 
perhaps a dozen abrupt drops in amplitude, by about 30%.  The drops are 
simultaneous in both IFs, but are always 'single' -- the next 1.67 
second record is at the proper level.  The B and D IF behavior shows the 
same drops (simultaneously with the A and C), *** and in addition*** 
have major and long-lasting changes in amplitude -- by a factor of two.  
The phase behavior of this antenna is terrible -- large (> 50 degree) 
jumps, probably coincident in time with the amplitude jumps.  The phase 
jumps are never 'single' -- the jump in phase is retained for tens of 
seconds until another jump -- which rarely returns to the same phase.

    2)  I had a fairly long slew between two sources -- a change in 
azimuth of 70 degrees, and a lowering of elevation from 71 to 35 
degrees.  Subsequent sources were also at a low elevation.  When the 
antennas arrived the source, notable changes in phase had occured on some:

    * Antenna 14 phase decreased by 100 degrees (all IFs)
    * Antenna 16 phase increased by 20 degrees. 
    * Antenna 21 phase increased by 100 degrees. 
   
    All others (except 24, for which no measurement could be made), 
showed no discernible change. 

    Question to RT phase experts, and temperature-elevation experts:  
Are these changes compatible with expected sensitivities?  (Note that 
antennas 13, 14, 18, and 24 are stated to have RT phase installed and 
working).