From: <richard.dodson_at_email.protected>
Date: Tue, 30 Mar 2010 18:32:00 +0800

Hi Cormac

   I am glad that we have managed to understand the rates at Ceduna.
If it is a correlator error it is _so_ much easier to fix.

  I have not been able to find exactly what it is in the CLCAL which
simplified the rates to a bimodal distribution. To do the polarisation
I apply the calibration in steps, first the delays, then the solutions
from one polarisation, then the long term offsets between the two
polarisations.

  I did fail to zero the phases in the application of the SN tables,
which reproduces the effect. I.e. The phases, when wrapping slowly,
corrects the rates to zero. When they are wrapping fast they can not
follow the changes, and we flip to the `other' rate.

 However my understanding of CLCAL says that the phases are not
included when using interpolation 'POLY' (which is the mode I am using
it in).

  Anyway I am glad that my analysis has uncovered some problems, even
if they are not what I thought at first. Maybe the usage of CLCAL has
changed.

   ATB

                    Richard

On Tue, Mar 30, 2010 at 10:56 AM, Cormac Reynolds
<c.reynolds_at_curtin.<!--nospam-->edu.au> wrote:
>hi all,
>
>just to follow up on this. Eagle-eyed observers will have noticed that
>in the figure I posted there was a clear trend in the phase rate as a
>function of hour angle, even though it wasn't the sharp jump seen in
>Richard's previous plots. I've confirmed that this is due to an error
>in the position of the Ceduna telescope used in correlation.
>
>It turns out we have been using an outdated position for Ceduna in
>correlation for the last few months (the error crept in when we
>updated to DiFX-1.5.1). The error is a couple of meters. Fortunately
>the fix for this is straightforward in AIPS and Hayley will contact
>all affected PIs shortly.
>
>Richard - any chance you could update your wiki page appropriately.
>It's a bit misleading at the moment.
>
>cheers,
>Cormac.
>
>On 22 March 2010 14:44, Cormac Reynolds <c.reynolds_at_curtin.<!--nospam-->edu.au> wrote:
>>hi Richard,
>>
>>I've taken a look at the vx014b data to investigate the 'Ceduna
>>problem', and have been unable to reproduce your plot showing Ceduna
>>going funky when the Hour Angle changed sign
>>ftp://ftp.atnf.csiro.au/pub/people/vlbi/incoming/CEDUNA_ODD.PS.
>>
>>Please take a look at:
>>ftp://ftp.atnf.csiro.au/pub/people/vlbi/incoming/CEDUNA_NOTODD.PS
>>to see my results. Ceduna looks quite well behaved in its rates and
>>delays. The SNR is not really good enough to determine if it is
>>exhibiting the very short timescale phase wander that has been the
>>hallmark of this problem so it's not a great dataset for diagnosing
>>that particular problem.
>>
>>Are you sure your data were from vx014B? Did you do some additional
>>processing before running fring? Could you possibly run 'md5sum' on
>>your fits file and send me the results so I can compare it with the
>>file on our archive to check for possible data corruption?
>>
>>cheers,
>>Cormac.
>>
>>On 5 March 2010 05:30, John Dickey <John.Dickey_at_utas.<!--nospam-->edu.au> wrote:
>>>Dear Richard,
>>>
>>>  That is odd behavior.  But I only have one plot, did you attach more?  The
>>>one I got is 4.2 Mby, a bit much for just 25 or 30 points to display.  There
>>>seem to be frequent jumps from low rate to high rate, but both are pretty
>>>consistent.  A wrap problem is possible, but we just replaced all the
>>>cables, all the way from the receivers to the control room.
>>>
>>>  Anyway, if there were more figures in your mail, could you please compress
>>>them and resend?  Thanks for your help.
>>>
>>>cheers,
>>>jd
>>>
>>>On 05/03/2010, at 2:00 AM, Richard Dodson wrote:
>>>
>>>>Hi Tassie-siders
>>>>
>>>> You must tremble every time I get some data. Here is something from
>>>>VX014B which _might_ help with the Ceduna problems.
>>>>
>>>>  After a few steps to remove basic instrument offsets I get these
>>>>residuals.
>>>>
>>>>  See how Ceduna has a high rate about 1/2 the time? (page 1, PL 4).
>>>>I thought at first that a source must have a very bad position, or
>>>>that the antenna position must be bad and only sensitive to some
>>>>source coordinates.
>>>>
>>>>  But compare that to Ceduna (and everyone else) plotted against
>>>>Hour Angle. When HA is negative rates are low. When HA is positive
>>>>rates are high. (page 2 PL 2, page 3 PL 3).
>>>>
>>>> Odd behaviour at Ceduna - Who would have believed it?
>>>>
>>>> I am guessing that what we see here is a change of rate when the
>>>>wrap changes, which I guess means that something is getting stretched,
>>>>but I don't see what that would introduce a rate change.
>>>>
>>>> Phases are fine pre-HA=0, all over the shop post HA=0. (page 4, PL 5
>>>>for amplitude RMS, page 5 PL 7 for phases).
>>>>
>>>>
>>>>  Have fun with this info!
>>>>
>>>>              Richard
>>>><CEDUNA_ODD.PS>
>>>
>>>
>>
>>
>>
>>--
>>----------------------------------------------------
>>Cormac Reynolds
>>Phone: +61 8 9266 3785
>>Fax: +61 8 9266 9246
>>email: c.reynolds_at_curtin.<!--nospam-->edu.au
>>----------------------------------------------------
>>
>
>
>
>--
>----------------------------------------------------
>Cormac Reynolds
>Phone: +61 8 9266 3785
>Fax: +61 8 9266 9246
>email: c.reynolds_at_curtin.<!--nospam-->edu.au
>----------------------------------------------------
>
>
Received on 2010-03-30 21:32:35