[evlatests] EVLA Tests Meeting

[Vivek Dhawan]

Here is a 'state of play' overview for today's test meeting.
We may not get to all of these, so I thought I'd spam y'all.

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        			 User-centric Checklist

  Fixes put in and tested:

  	Correction for amplitude non-closure from large ~100ns
  		delay errors across single channel (Aips/Eric)

  	F_shift correctly accounted in turning delay into phase
  		(Barry)



  Phase transfer accuracy now:

  	< 60 deg max error, whole sky, at L,S,C,X.

         < 60 deg max error at K, Ka, Q across 35, 25, 15 degrees.

  	 i.e. image position better than 1/6 beam for cal/target
          separation closer than quoted number. This is limited by
          antenna hardware (aside from weather). Correlator model
          errors are unmeasurable now - 5 ps or better on timescales
          of a few minutes to a few hours.



  Image dynamic range, at tracking center.

  	No sweat: 30K:1 or better, L, C, X band
  		  without BLCAL

  	Noise reduction with N_chan: L:not.  C: sorta - see next.

  	Reaching thermal noise
  		I/V image on a few-Jy point source:
                          factor 5 or more @ L
                          Factor ~2 @ C, X.

  		Blank field: within factor 2.

  	Possible causes:

  		Delay rocking - remove with short fringe fit.
                        probably not the major cause.

  		Bandpass stability: few parts in 1000, A&P.
                        slow variation over several minutes
                        self-cals out, I think.

                 Beam squint - not important(?) on point source
                        at phase center, w reasonable pointing.
                        (?Check via Sanjay's software in CASA)

  		D*D terms, unpol source: should partly self-cal out.
                        frequency dependence may not self-cal(?)

  		Source spectral index: should partly self-cal out.
                        (each subb is normalized & self-cal'd.)

  		Wobbles - known to violate closure, so let's make
                           them the scapegoat till they're gone.

  		      * Period shortens as F_sky increases, LCX.
  		      * Amplitude decreases as F_sky increases.
  		      * Wobbles are much faster than delay rate.
  		      * There is no delay wobble, only A&P wob.

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