[evlatests] Failure to tune, continued ...

[Rick Perley]

    I ran another L-band polarization experiment last night.   In this 
experiment, 11 different tunings in spectral line at 12 MHz BW 
alternated with a continuum observation at 50 MHz.   There were many 
failures to tune, with some interesting -- and I hope revealing -- 
patterns. 
   
    The 11 different spectral line observations were taken in mode ' 
PB', from 1100 to 1990 MHz.  Each was one minute long.  The 50 MHz-wide 
continuum observation, also one minute long, was made at the standard 
frequencies (1465 and 1385 MHz), and followed the 1990 MHz 
observation.   The entire observation extended for 5.5 hours (01:00 
through 06:30, IAT). 

    The following remarkable 'failures to tune' occurred **in the 
continuum data**.  I haven't reviewed the spectral line data yet. 

    1) Antenna 14A and C stopped producing fringes one hour into the 
run, and never recovered.  This failure was flagged by the system.  14B 
and 14D continued on, without any problems. 

    2) Three EVLA antennas either failed to produce fringes for some 
scans, or were late to provide fringes.  This occurred ***only on IFs A 
and C***.  The affected antennas were 1, 18, and 26.  Of these, antenna 
1 was easily the worst (it was late to start fringing on 5 of the 32 
scans).  None of these failures were flagged. 

    3) The EVLA and VLA were incoherent with each other on one scan 
(03:21:45 through 03:22;38, IAT) -- on IFs A and C only. 

    Note that there were no failures -- of any kind -- in IFs B and D.  
The data (other than the persistent first-record problem) were perfect 
in every way. 

    I'll review the 11 spectral line tunings next (all taken in IFs B 
and D only), to see if there are more curious characteristics to report.