Minutes, CA-forum #14
Tuesday, 30 April 1996
1. Tied-Array phaseing.
CACAL was modified to provide the option to phase the array for
tied-array purposes ... a 90 degree phase shift between X and Y is
introduced. Further work is required:
a. An additional option: + or - 90 degrees.
This option should be offered in terms of : "R and L" (opt. 1)
"L and R" (opt. 2)
b. CACAL needs to be sensitive to the conversion chain - the
sideband is important.
>>> WEW will consult his Galileo notes to determine the correct
labelling - ie, to make it consistent with the definitions used
by JPL in their processing.
MJK to provide the LO-CHAIN details.
DMCC to arrange the modifications to CACAL.
1.a The LO parameter files at Narrabri should be placed in a CMS
environment. The Narrabri and Mopra files should be brought back into
line - Mopra files were recently modified.
>>> DMCC to arrange.
2. Data Quality Observations.
The observations have been made after almost all the reconfigurations.
The analysis is now up to date.
The automatic processing needs some further refinement - the automatic
flagging is not entirely satisfactory, as it can flag some good data
and not flag some bad data.
>>> R.S. and M.W. to investigate.
The time to process an observation is around a half-day. It seems that the
baseline and pointing calibrations are adequate to find the immediate
problems with the array - the DQO have not found problems which required
immediate action. This suggests that while it is desirable to process
the DQOs as soon as possible (to avoid serious backlogs building up),
this is not an operational matter - processing could be postponed, for example,
at times of frequent reconfigurations.
R.Sault will maintain a watching brief over the long term trends.
The reporting of the results - the present output is very comprehensive
and thus hard to digest. R.S. will look to simplifying it.
Is the data good enough for the Hubble blank field project?
R.Wark and J.Higdon will collate all the data collected so far on the blank
fields. This will give us an indication of what we might be able to
contribute to the Hubble Blank Field project.
3. S-band off-axis polarisation.
a. R.Sault and M. Ehle have recently made a series of observations
to assess to problems - the prognosis is poor, with serious spurious
polarisation appearing at the beam half-power area. (10% or so).
The problems can be modelled - this is being pursued. It appears
that to first order to matter can be corrected, reducing the
spurious polarisation to 1-2 % levels. Second and higher orders
cannot be treated, and do not cancel. In this problem software
is unable to repair a hardware problem - a rebuilt OMT is required.
b. An additional narrow band problem, specific to antenna 4 has been
seen - there is a spurious 2% leakage term appearing in just the
X- products of antenna 4. It is thought to be confined to L-band
This problem was seen in the Nov. 95 data; it was still present
on 27 april 1996.
>>> WEW will investigate, on friday 10 may, 8:00 tp 10:30.
4. Precision of stored positions -
R.Sault, J. Reynolds and D. McKay will pursue this ... there is some
confusion as to what has been fixed.
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next meeting : Friday, May 24, at 11:00 am.