[mmaimcal]Re: ACA Phase Calibration

[Stephane Guilloteau]

Hi Mark,

    I fully agree with the conclusions, but someone should work on proper use of a WVR for the ACA.

There are two reasons for that:
     - Phase calibrating the ACA will too frequently would INCREASE the phase noise on these short baselines.
    (essentially you add up the phase fluctuation on the calibrator to the ones on the source, and they are uncorrelated
     on short baselines and short timescales)

    - Yet, with the WVR, the maximum time between calibration is given by the WVR stability. One should look
    whether there is any conflict with the above minimum time between calibrations...

More generally for ALMA, improper use of fast switching will increase phase noise on short baseline. Can we solve for
phases on different timescales for short and longer baselines ? More precisely, can we do that without induly breaking
phase closure ? There is a some research to be done in an optimal calibration technique from this point of view...

A related point: I did not get how you would increase the S/N on the ACA antenna gains by not solving for the 12-m
antenna gains when they are cross-correlated together. How do you get the gain of these 12-m antennas then ? And how
does the error on this gain (which necessarily exists) reflects on the error on the ACA antenna gains ? Doesn't that
cancels to some extent the improvement obtained in S/N ?  I believe you should detail your calculation there.

        Stephane





Subject: [mmaimcal]Re: ACA Phase Calibration


>
> Moderator: KILL the version of this message
> that attempted to send the 0.2 MB file to EVERYONE.
>
>
> Everyone:  please find the draft memo in:
>
> http://www.tuc.nrao.edu/~mholdawa/aca_phase_writeup.ps
>
>   -M
>
>
> > And now for something completely different!
> >
> >
> >
> > Here is a draft memo which argues:
> > ---------------------------------
> >
> > ACA baselines are so short that you don't need phase calibration.
> >
> > The Weather is so unpredictable that the ACA needs dynamic scheduling.
> >
> > Fast switching won't help the ACA.
> >
> > WVR could help increase the efficiency of the ACA.
> >
> >
> > BUT:
> > ====
> >
> >
> > If the ACA is going to get correlated with ALMA,
> > the ACA antennas absolutely need fast switching and WVR.
> >
> >
>
>
>
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