[evlatests] Pointing

[Rick Perley]

    The EVLA Checkup done today employed referenced pointing at all 
bands except L-band.  Some curiosities were noted ...
    For C, X, and K bands, I used only 'primary' referenced pointing, at 
the frequency of observations.  (That is, rather than following the 
standard procedure of using X-band pointing to peak up any given band, I 
used observations at the required band directly.)  For Q-band, I did a 
primary reference pointing at K-band, then 'tweaked' it via secondary 
pointing at Q-band. 

    1) The most curious is that antenna 16, despite giving good fringes 
of normal amplitude on all IFs and bands, failed all pointing solutions 
at all bands.    How can this be? 

    2) Antennas 18 and 20 have *humongous* pointing errors -- easily 
explaining the lack of good fringes from them at X-band and above: 
      
             Antenna 18:  The C-band pointing shows offsets of 1.5 and 
-2.5 arcminutes in Elevation and Azimuth, respectively.  Unsurprisingly, 
referenced pointing failed at X, K and Q bands on this antenna. 

             Antenna 20:  Both C-band and X-band pointing shows offsets 
of 1.8 and 1.2 arcminutes in El and Az.   Unsurprisingly, referenced 
pointing failed at K and Q bands. 

    Both of these antennas were moved recently, but I did not think such 
large errors would result.  (Ken, Barry -- is this normal?) 

    Antennas 1, 2, 7, and 27 have also been moved recently -- all have 
modest (< 1 arcminute) pointing errors.  A pointing run this evening 
would be beneficial.  Because of the large errors in 18 and 20, I 
recommend the pointing be done at C-band.