[evlatests] Superb L-band behavior, and holography update

[Rick Perley]

    A short observation last night at L-band (for holography tests) 
shows fabulous VLA and EVLA behavior.    This was done in continuum, 
with 6 MHz BW, with 0.418 second integration. 

    In particular: 

    1) The curious and very common dropouts that we have been seeing for 
months on antenna va4 are gone! 
    2) The equally curious dropouts on ea11 (L-band only) which were 
always three 0.418sec records long, are also gone! 

    The only fast-scale amplitude and phase effects notable are the 
'short shallow drops', which are of no consequence to astronomy. 

    But -- nothing's perfect.  Two problems remain:

    1) I included, as normal, a 'dummy' first scan.  As is almost always 
the case, the EVLA and VLA had a global phase shift between this first 
scan, and the following scan -- which was identical in all system 
parameters.   There were no other phase problems in the calibration data. 

    2) The first holographic 10-second dwell had a different phase than 
the preceding, and following, 10-second dwell.  This phase offset is 
different for every EVLA antenna -- it is not a 'global' effect in the 
sense of that described above. 

       For Bryan/Walter/Barry/Ken, I offer the following extra information:

       When a holography scan is initiated, there is a 'submode=0' 
observation (ten seconds, usually) during which the antennas are clearly 
moving and getting organized.  Since the offsets are small, in my tests 
the antennas take much less than 10 seconds to get organized, so I can 
see what the system phase is.  The phases of this 10-second duration are 
correct.
       The next 10-second interval has the incorrect phase.  This 
interval is always 10 seconds long, even if I request a 20-second 
duration for each holographic position.   This position is 'submode=1' 
-- the first legitimate holographic observation. 
       The next 10-second interval (submode = 2 if I have 10-second 
dwells, or submode = 1 if I ask for 20 second dwells) has the correct 
phase. 
       All other holographic positions have the correct phase. 

    So far as I can tell from quite exhaustive tests done last week and 
over the weekend, all other aspects of EVLA holography are working 
correctly.