[evlatests] No Referenced pointing for VLA antennas

[Rick Perley]

    I ran a K and Q band check, using the last 30 minutes of software 
time.  The goals were to see how well these bands are operating, and to 
check whether referenced pointing is working. 

    Observations were made in continuum, on 3C286, which was near 
transit.  Two observations at K-band, and one at Q-band, were made.  
Referenced pointing -- done at K-band -- was done for each of the three 
observations.  Following the determination, a short scan with the 
correction applied, and another with no correction applied, were made to 
see if the expected improvement in visibility amplitudes were seen. 

    The referenced pointing solutions were printed out -- all working 
antennas gave good solutions, with the exception of 15, 11, 21, and 
23.   Anttennas 15 and 21 gave solutions, but the amplitudes were rather 
low, usually indicative of a problem.  The other two were non-functioning. 

    Major Result:

    ***  The solutions are not being applied, or not being applied 
correctly, to the VLA antennas.  In most cases, VLA antenna amplitudes 
were the same with and without the referenced pointing solutions being 
applied.  Furthermore, for those VLA antennas with large pointing 
errors, the amplitude solutions showed the types of temporal modulation 
expected when the source is on the side of the team.   
    One can make a case that the VLA antennas are being corrected when 
the offset to be applied is small.  But when large (0.5 arcminutes or 
so), it is clear that the applied correction (if any) is not right. 
          By contrast, the EVLA antennas showed in every case the 
amplitude gain expected with application of the pointing corrections. 

    This behavior was seen both at K and Q bands. 

    Minor Results:

    1)  Antenna 14 clearly has something wrong with its pointing model.  
K-band referenced pointing worked well when applied to K-band 
observation, but actually worsened the amplitude at Q-band, when applied. 

    2) Antenna 18, in IF#1, is showing significant phase jumps within a 
scan.  The jump is 50 degrees or so, and is the same in the two 
polarizations (A and C).  IF#2 is not affected.  The behavior is the 
same at both K and Q bands. 

    3) Most of the VLA antennas showed a significant visibility drop for 
the last 5 seconds of the run (at K-band).  None of the EVLA antennas 
showed this. 

    4) Antenna 14 was slow to stabilize its phase at the beginning of 
the run.  Only this antenna showed such an effect.  I had to remove 
about two minutes' worth of data. 

    5) A 'dummy' initial scan was put in, to see if the initialization 
troubles occasionally reported showed up.  The first scan was in fact a 
good one (other than antenna 14, as noted above).