ATCA Current Issues

Poor Sideband Rejection in mm Receiver (18-Sep-2008)

Poor rejection of the second sideband image has been identified in 7mm ATCA data. It is also probably an issue for high frequencies (above 100GHz). Some frequencies should be better protected against this problem. For continuum observations at 7mm we recommend 34496/34624 or 44096/44224 as the observing frequencies. For more information, talk to the Duty Astronomer.

Legacyserver running on xbones (18-Oct-2008)

Legacyserver is currently running in the background on xbones. Do not be alarmed if you cannot find it on the skull window it has been running on for the last year or so. It is now part (again) of atdaemon, so if you need to restart it, just do an atdaemonrestart, and then restart CAOBS

Accidental online selfcal in CAOBS (10-Sep-2008)

In a small number of observations between April 2007 and September 2008, the selfcal function in CAOBS (developed as part of the array's satellite tracking capability) was inadvertently switched on. We have identified these occurrences and notified affected observers. To restore the phases in data with selfcal switched on in CAOBS see this link.

Changes to the Seeing Monitor (10-Sep-2008)

The Seeing Monitor uses the 30GHz beacon on the Optus B3 communications satellite. The satellite (which has been in service since 1994) has been replaced however the new satellite does not have an equivalent beacon.

In January 2008 the Optus B3 satellite was be moved to a new sky position. During this time preiod, the Seeing Monitor dishes were regularly repointed in an endeavour to maintain Seeing Monitor operation, however, there were unavoidable outages.

Once in its new orbit, orbit instability gradually increased and Seeing Monitor was not always available, with the satellite drifting out of the Seeing Monitor beam twice each day.

In September 2008, we have replaced the Seeing Monitor receivers and now use a different frequency beacon on the Optus C1 satellite, and so have returned to having full Seeing Monitor availability all day, every day.

Mosaicing with Short Cycle Times (10-Oct-2007)

Mosaicing will not work with cycle times less than six seconds. More specifically, it will appear to work, but the flagging applied when the antennas are moving between positions, may not be correct.

New Observing Commands (6th July, 2007)

(- mostly for NASA tracks)

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mm Focus position (22nd May, 2007)

For many years we have not had to concern ourselves with setting the focus of the antennas. However with the arrival of 7mm receivers, we need to start giving this some attention.

For the present, observers are advised to set the antenna focus according to levels given in the following table.

ant	7mm	3mm
1	16	13
2	9.8	9.5
3	9	9
4	23	23
5	18.5	18.4
6	?	-

Focus is set in caobs:
caobs> focus ca0# mm

Focus can be checked in monica:
monica => navigator => misc => subreflector => focus

C26 Splitter Module Power Levels (updated 7th June, 2007)

For mm observations (i.e. 12, 7 and 3mm), the power levels in the C26 splitter modules to should be less than the saturation limit (20v). There is a caobs pattern that should look after this (and set coarse attenuators)
In caobs, caobs> chklev # (where # is the scan number of the calibrator scan)

After this, you will need to check that the coarse attenuator levels and, if necessary, set the coarse attenuators so that the fine attenuators are in the middle of their range (i.e. at levels of 2-5)

Details (from 22nd May)

These levels are displayed in monica.
monica => navigator => conversion => freq1_summary.
The relevent numbers are the 3rd - 5th lines. (The B pol on antenna 2 has a problem and is not reading correctly)

Setting these levels is done with the mm attenuators. To determine current mm attenuator settings:
caobs> sho mm
The values of each mm attenuator are displayed in the middle caobs pannel.
To set the mm attenuators:
caobs> set mm ca0# A B
where A and B are the attenuator levels (0 - 15) for the A polarisation and B polarisation.

For 3mm observations, this should be done with the paddle in:
caobs> set paddle in.
At the end of the attenuator settings, don't forget to remove the paddle
caobs> set paddle out

New Maintenance Commands (20 April, 2007)

• caobs> disable atten disables all changes of attenuators, useful for receiver testing only (use enable atten for normal operation)
• caobs> atten_init 4 1 7 initialize attenuator settings for all antennas, IFs and frequencies. First number is the fine attenuator, second number the coarse attenuator, last number the mm attenuator

New reference pointing mode (22 March, 2007)

There is a new pointing keyword in sched, OFFPNT, which is like OFFSET, but instead of selecting the most recent pointing solution, it selects the one nearest on the sky to the current position (in Az/El). This should allow you to do e.g., reference pointing for snapshot observations or observations of several sources with large separation. The search is currently limited to at most 2h in time and 25 degrees in distance. These numbers could be changed (or made user selectable) in reponse to observer feedback.

New mosaic mode (12 March, 2007)

There is a new scantype in sched, OTFMOS, which is like MOSAIC, but instead of moving from point to point, the antennas scan continuously across the mosaic points. For more details see OTF mosaicing. It should be noted that Miriad has not yet been modified to image the data correctly.

Starting generators without stopping a scan (15 December 2006)

The installation of "synchronisers" on the generators means that it is no longer necessary to stop a scan before turning generators on or off.
(The commands remain the same - see new caobs commands.)

As always, you should monitor the power changeover to ensure that all the generators take the power load: Check the PMON rack or monica pages

CAOBS first scan problem (November 2006)

The problem (under linux) of the first scan of CAOBS being bad remains (but it appears not everyone reads that far down this page!). As outlined below, The first scan after CAOBS starts (or is restarted) is always bad Either CACOR gives red "DELBAT" error messages/no good data OR the delays are bad and 8 ns delay jumps (early-normal errors) appear. These errors may sometimes also appear after typing start later in the run. Pending a more elegant solution, the answer is to simply stop the scan and start it again and the errors should go away.

Sched under linux (= atcasched) (October 2006)

Observers should now use the linux version of sched to make their schedule files. The linux version of sched is called atcasched, but in other respects it is very similar as the VAX version. To make, or revise, a schedule file from within ATNF, ssh to the atcaobs account on xbones. (From the SUNs, you may need to specify ssh2.) From outside ATNF, first log in to your own account on nelle, then ssh to the atcaobs account on xbones, or download the scheduling program to your own machine (see the sched webpage for details).

As linux does not give each revision of a schedule file a new version number, observers are advised to back-up all important schedule files to their own computers. Also, when naming schedule files, remember that linux is case-sensitive!

Remote Observing (October 2006)

Remote observing For the OCT06 semester we are trialling a relaxation of the requirements for ATCA remote observing. It will still be the case that remote observing will only be granted to astronomers who have observed with the ATCA in person at Narrabri within the previous 12 months, however other restrictions on the amount of remote observing within any given time interval will be relaxed for the duration of this semester. The conditions for remote observing are given on the ATCA Remote Observing page.

CloudSat (June 2006)

Cloudsat is a NASA satellite mission providing observations to advance our understanding of cloud abundance, distribution, structure, and radiative properties. CloudSat has the first satellite-based millimeter-wavelength cloud radar, allowing detection of small particles of liquid water and ice that constitute the large cloud masses that make our weather.

So much for the advertising - It's a nice experiment, but that radar has the potential to destroy our 3mm receivers.

Operationially, we need to ensure that we do not have the mm receiver on axis, at an elevation of greater than 88 degrees when there is a Cloudsat pass over the ATCA or Mopra. To this end, we have modified the ACC software so we can't park the antennas with the mm receivers on axis and we send emails warning ATNF staff and visitors of Cloudsat passes greater than 85 deg for ATCA and Mopra. For more information see the Satellite Overpass Closest Approach Predictor

If you are observing with the mm receiver, please check that your observations will not risk the receiver and be prepared to do something else for a few minutes if there is a risk of this.

Linux CAOBS (23 December, 2005)

Sched

The scheduling program sched is now run on xbones as atcasched. Both schedule files and mosaic files that were stored on a VMS filesystem have been copied across to xbones to the following directory paths:

Working with these directories is awkward because they contain a lot of files, so it takes a long time (minutes) to get a directory listing.

Task: print a schedule listing

• while logged in as atcaobs on xbones
• print the file with a2ps:
  xbones$ a2ps -Pcalaser1 -r --columns=1 -l 132 /atomsexport/caobsonline/caobs_sched/sched.lis
  or lpr:
  xbones$ lpr -Pcalaser1 /atomsexport/caobsonline/caobs_sched/sched.lis

Task: upload a new mosaic file from your account (abc123) on, e.g., kaputar

• log in to xbones as atcaobs
• copy the file across
  atcaobs@xbones$ scp abc123@kaputar:mysource.mos /atomsexport/caobsonline/caobs_mosaic/
  Note that filenames are case sensitive on Linux, see below.

Task: copy your sched files for safekeeping

• log in to, e.g., kaputar
• copy the file across, e.g. to your schedules directory:
  kaputar$ scp atcaobs@xbones:/atomsexport/caobsonline/caobs_sched/yourschedfile.sch schedules/

Known Linux CAOBS Problems (and solutions)

The 'Stop/Start' Problem

The first scan after CAOBS starts is always bad: Either CACOR gives blue "DELBAT" error messages / no good data OR the delays are bad and 8 ns delay jumps (early-normal errors) appear

These errors happen on the first scan after CAOBS is re-started, but may sometimes also appear after typing start later in the run. Simply stop the scan and start it again and the errors should go away.

CAOBS hangs or refuses to respond to commands as expected

The sequence that leads to this problem are unclear. To recover, <ctrl>c and restart caobs. (Note: You will then have to be careful of the 'Stop/Start' problem.)

Case-Sensitivity issues

In VMS there is no destinction between upper and lower cases.
Linux does care about case, so take care.

A good solution has been to consider all files to be lower case. This seems to be what most people do, however, not everyone, so there can be confusion especially with mosaic files.
In Brief: Use lower case to refer to all mosaic files in sched .

New Linux CAOBS Commands

On 12 October 2005, the ATCA calibrator catalogue, calibrators.cat, was updated with 86 improved positions and 4 new sources. People who have high astrometric needs or who have multi-configuration observations with schedules created either side of 12 October may be affected. A separate web page gives more information.

The 3mm and 12mm tuning system has a few limitations which may be unanticipated by those who are familiar with centimetre operation.

• Frequency 1 and 2 cannot differ by more than 2.7 GHz when observing in two frequency mode.
• If you change frequency settings at 3 and 12mm, then the instrumental phase can change. The instrumental phase can change for both frequency 1 and frequency 2, even if only one of these two frequencies was changed. You are advised to redetermine antenna phases with each frequency setting.

The computer ``kaputar'' is the main compute server. To find an area with a large amount of disk space to work within, use /DATA/KAPUTAR_3.