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ATCA Current Issues

7mm polarization data (09 Mar 2010)

If you have processed 7mm polarization observations with a miriad version older than 4 Mar 2010, the polarization angles will be off by 90 degrees. You can either flip the sign of Q and U in your final images or reload the data with the latest version of atlod and redo the reduction. [If you loaded 7mm data with the miriad version from 18 Feb 2010, you are advised to reload it with the latest version, as it contained an incorrect fix which made the problem worse.]

Saving tvchanels (29 Jan 2010)

tvchan settings in CABB define the channel range over which data is averaged and passed to caobs. This range is also used to generate the Tsys values in the RPFITS file headers.

Thus, if these channels are not changed every time there is a change that would need different channels, the Tsys values will not be correct.

Mark Wieringa has implemented a new field in ATCAsched which can define a channel range. The parameters are four, comma separated, values representing (in order) the first and last tvchan for IF 1, and the first and last tvchan for IF 2. If it is left as blank (or null) then the correlator tvchan settings are kept, otherwise this field will override the correlator settings. These tvchan settings are settable for each scan.

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Block errors in CABB

If a section of the SPD amplitude plot has approximately every second channel set to zero, a cabb slot has died and needs attention

To solve,

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Delbat errors in CABB (24 Aug 09)

If observations are stopped and restarted too quickly, there will be correlator timing errors

To solve, stop, wait 2 - 3 cycles and restart

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Primary calibrator fit updates (17 Aug 09)

The built in flux model for 1934-638 has been updated with recent measurements by Jamie Stevens in the 7mm band. A new fit for the frequency range above 10 GHz was derived. It connects smoothly to the existing low frequency model (<10GHz) and replaces the previous high frequency fit which was based on 12mm data only. The addition of 7mm data caused a small change in the slope across the 12mm band, fluxes at the edges of the 12mm band have changed by up to 5%. [Update: the Uranus flux model used to calibrate this fit may have problems, details are here]

C26 Power Levels (10-Jul-2009)

It has become aparent that it is important to work hard to ensure that the CABB sampler values are as close to 20 as possible (i.e. 10 is not close enough). At mm frequencies this generally means that the mm attenuators have to be set to low numbers. It is no longer necessary to ensure that the power levels into the C26 modules are less than 20V.

The following values are given as representative starting values for the mm attenuators
Freqenciesmm Attenuator Levels
17GHz/19GHz3 3
33GHz/35GHz0 0
43GHz/45GHz3 3
93GHz/95GHz0 0

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cacor reset Commands (9-Jul-2009)

Warwick has created some new cacor reset commands to help us get out of strife if we have managed to set the delays or amplitudes to outrageous values.

cacor> reset delays resets delays to nominal values for this antenna config
cacor> reset acal sets the cal step in Jy back to 10 Jy (or some nominal figure)
cacor> reset abdelays sets the b delay equal to the a (incase they get out by a long way)

If the AB delays are exactly 0, the issue is generally that delavg has been set to many cycles and ab phases are wrapping so rapidly that the system is averaging to 0.
The solution is to cacor> reset abdelays and recalibrate

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Mosaic file limitations (10-Jun-2009)(updated 07-Jul-2009)

There is currently a limit of 500 pointings per mosaic file. The correlator will stop working if you use more than that.

There is also a limit of 8 characters on the mosaic field name (excluding the required $ sign). This means you can use names like $1934-638, but NOT $1939-6343. Fields with names that are identical in the first 8 characters will have the phase tracking for the first field applied (but with the position offset for the current field).

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L86 oscillator unlocked and RT freeze (25-May-2009)

When changing frequencies with the mm system, the RT process is responsible for setting the L86 LO frequency, which brings the sky frequency down to where CABB needs it to be. If RT freezes, then the L86 LO will not change to the correct frequency, and you will notice peculiarities with delay, phase and amplitude which may go away when you return to the previous frequency.
To check this, find the RT window on pericles (should be on the leftmost screen, near the top left), and check that it is updating every few seconds (it should output a couple of status lines with this frequency). If it is not updating, then you need to restart it.
To do this:


RT should then start updating correctly.
You will then need to stop and start your scan in caobs, and you may need to do this more than once; keep checking the L86 lock while doing this, keeping in mind it may take a few correlator cycles for the LO to lock. Sometimes you may also need to restart caobs to reestablish the connection with RT, but as long as you can see a frequency change request in the RT window when caobs starts a scan, then communication has been established.

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CABB shutdown and 2009APRS semester (05-Mar-2009 & 17-Nov-2008)

The six-week shutdown to remove the old correlator and install the new Compact Array Broadband Backend (CABB) was successfully completed in mid-April 2009. Follow progress during the shutdown on the CABB Diary webpage. The 2009 APRS semester will be the first to offer the full Compact Array Broadband Backend (CABB) capability. Due to the staged implementation of CABB modes, the 2009 APRS semester for the ATCA will run from mid-April to mid-July ONLY. For 2009 APRS, CABB will be available with a single coarse resolution mode with a bandwidth of 2 GHz and a spectral resolution of 1 MHz, corresponding to 2048 spectral channels. A separate call for ATCA proposals will be announced on 15 April 2009, with a deadline of 15 May 2009 for a '2009 JULS' semester. The 2009 JULS will run from 15 July 2009 until end-September 2009. ATCA proposals not scheduled in the 2009 APRS semester should be resubmitted for consideration in the 2009JUL semester. It is expected that one or more CABB zoom modes will be available for this semester. For more details, see the ATNF Telescope Current Status page.

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Flights to Narrabri (05-Mar-2009)

QantasLink will cease their service between Narrabri and Sydney at the end of March 30, 2009. Aeropelican, a Newcastle-based airline founded in 1971, will commence a direct service between Narrabri and Sydney from March 30. More details will be available from the Observatory Visitors Guide webpage.

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Leap Second Problems (21-Jan-2009)

A leap second added to UTC at UT 00:00 on 1 January.

We had thought we were on top of handling this, however it turns out that the ephemeris handling is more complex than originally recognised. The net result was that there is a 1 second timing error in data observed between UT 00:00 on 1 January and 13th January (up to the reconfig). It has been fixed now.

The error is not substantial, and it might be that it will not be noticeable for low frequency observations. However the effect becomes more significant at higher frequencies.

To correct the data use miriad "uvedit":
uvedit time=-1 vis=in-file out=out-file

This corrects the input data-set "in-file", and produces output "out-file". You should do this before any calibration.

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mm Receivers not always Locking (7-Nov-2008)

It is possible to choose mm frequencies whose LOs are outside specifications. This means that the receiver does not lock.

It is usually possible to find another frequency close to the original requested frequency which will allow the system to lock

To find a compatible frequency pair, use xbones> lo_chain

If the CX LO frequency is any of 5750, 5770, 6070, 6090, 6390, 6410, 8630, 8650, 8950, 8970, 9270 or 9290MHz, it is likely some of the receivers will not be able to lock.

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Pointing Offset Between mm and cm Receiver Packages

(7-Nov-2008)

There is a pointing offset between cm and mm receiver packages.

It is of order 20-30" and is most obvious on antennas 2 and 3

When mm observations are scheduled we generally provide a cm and mm pointing model - please contact local staff for current information.

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CACOR (6-Nov-2008)

We are running a new version of cacor.

If there are any problems it is possible to revert to older versions of the code by:
corr> cacorver version

Versions are:
previoussoftware that is robust, but does not have the pkchan command that is used for narrow bandwidth NASA tracks.
This version is from October, 2007
dangerousincludes the pkchan option, however has been known to hang when caobs is restarted
This version is from August, 2008
currentincludes pkchan option but no longer connects automatically to the GPIB/ethernet interface used for NASA tracking

To talk to the GPIB/ethernet innterface (required for NASA tracks):
cacor> gpib [i.e. this is typed in the 'command' text box at the bottom of the cacor gui]

To stop talking to the GPIB/Ethernet interface:
cacor> nogpib HOWEVER this command is suspected of causing the GPIB interface to hang in some, not yet understood, way. So, after using gpib in cacor, it is recommended that you exit out of cacor and restart it.

This version is from November, 2008

To check which version is being used:
corr> cacorvers

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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.

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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

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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.

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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.

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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.

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New Observing Commands (6th July, 2007)

(- mostly for NASA tracks)

Euan has added a couple of new commands to caobs to allow reattaching processes without stopping observing
caobs> rtconnect reconnects caobs to rt after rt is restarted
caobs> restart ca0# drives antenna # to position if it has stopped tracking during a scan
 
Mark has added caobs commands to turn the antenna 5 test tone on and off
caobs> set tton|ttoff turns the test tone on and off
 
Warwick has added a couple of commands to cacor to allow the selfcal on the spacecraft signal to work better.
cacor> sigch[an] x1 x2 [x3 x4] where x1 and x2 define the start and stop channels for frequency 1 (e.g. the spacecraft signal when doing NASA tracking), x3 and x4 are for frequency 2.
By default, "sigchan" also defines a range of channels to either side of the signal for the determination of the background. A linear fit is made to the amplitudes and phases of these channels and these are used to determine a (complex) background component at the signal channels, which is then vector subtracted from the signal.
The ranges of channels used for the background can be displayed with the "bg1chan" and "bg2chan" commands, without parameters. "bg1chan" is for the low channel range, and "bg2chan" is for the high channel range.
note: The default or reset command to reset the sigchan values is not valid for sigchan
cacor> bg1ch[an] x1 x2 [x3 x4] Manually sets the background range for the low numbered channels
cacor> bg2ch[an] x1 x2 [x3 x4] Manually sets the background range for the high numbered channels
note: Any subsequent sigchan command will cancel these inputs and return to the default background channel ranges.
cacor> tvch[an] def[ault] returns to the default channels

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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.
ant7mm3mm
11613
29.89.5
399
42323
518.518.4
6?-

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

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

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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

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New Maintenance Commands (20 April, 2007)

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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

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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.

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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!

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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.

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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.

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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:

Linux Name Linux Environment Variable VMS Name
/atomsexport/caobsonline/caobs_sched/ $ATCA_SCHED at$sched:
/atomsexport/caobsonline/caobs_mosaic/ $ATCA_MOSAIC at$mosaic:

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/
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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 .

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New Linux CAOBS Commands

With the implementation of the Linux observing system turning the generators on and running cain are done in a different way:

Cain

Cain tasks are now executed from within caobs with the following switches.
caobs> cain initresets integration clocks
caobs> cain cycle psets cycle period to p seconds
caobs> cain cycle default sets cycle period to 10 seconds
caobs> ppload uploads pparams.dat
caobs> ppglobal reloads global pointing parameters
caobs> ppfix nreloads pointing solution with given catag pntcom number n
caobs> reconfig clear clears all system delays (for experts only)

Generators

Antenna generators are still started with a caobs command, however, the format has changed slightly (and all the questions have been removed).
caobs> set genset_on ALLturns all generators on (including the control building generator)
caobs> set genset_on CA0#turns antenna # generator on
caobs> set genset_on CBturns control building generator on (including the control building generator)
caobs> set genset_off ALLturns all generators off
caobs> set genset_off CA0#turns antenna # generator off
caobs> set genset_off CBturns control building generator off

Other

caobs> selfcal on [circ|lin] switch on phase selfcal for tied array observations, option CIRC adds a 90 degree phase shift between the X and Y polarization to create circulars
N.B. do NOT use this for interferometry observations
caobs> selfcal off switch off phase selfcal for tied array observations
(Note: case matters)

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New calibrator list (12 October 2005)

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.

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mm Frequency restrictions

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

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Data disks and computing

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.

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Original: Robin Wark (19-Jun-2003)
Modified: Mark Wieringa (07-Jul-2009)
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