[evlatests] Slow Pointing Wobbles

[Rick Perley]

     I promise this is the last piece of 'JVLA Spam' for a while ...

     Analysis of the gains provided by the extensive observations of 
3C273 reveal some other disturbing behavior -- slow wobbles.

     In short -- *all* antennas display this phenomenon at one time or 
another.  At the higher frequencies (K, Ka, Q bands), the gain solutions 
commonly undulate with a typically 4 minute period.  For most antennas, 
the amplitude is small -- perhaps 2% in voltage.  At 30 GHz, this will 
be seen with a ~15 arcsecond pointing offset from center.  (If there is 
a pointing error, the observed effect will be seen with a much smaller 
offset).

     For most antennas, the effect 'comes and goes' -- it is seen on 
some scans, and not on others.  Although 15 arcseconds may seem small, 
it is significant for high-frequency observations of objects with 
angular scale similar to the antenna primary beam.

     For two antennas, the effect is *much much* larger.  I include two 
plots, showing them.  The amplitudes are very much larger -- indicating 
offsets of an arcminute or more.

     Is this an encoder issue?

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