3mm ATCA Quick Start

The commands below should get the telescope set up and ready to make observations at 3mm. However they only cover the typical case. After reading this you should discuss with your DA what you will need to do to get set up.

You will need to type in more than one window — check you are typing in the correct one before entering a command.

Stow any unusable antennas and detach them. CA06 does not have a 3mm receiver:
```
 caobs> stow ca06 
 caobs> detach ca06 
```
It is ok to detach antennas while they are stowing
Load your observing file:
```
 caobs> set file [your-schedule-file] 
```
Ensure the focus on antenna 1 is correct ¹ (in MoniCA, look at the page Misc:Subreflector Focus). After loading your 3mm schedule file in caobs, you can simply type
```
 caobs> focus default 
```
Start tracking a bright (> 5 Jy) continuum source from your observing file (n is the source number in your sched file)
```
 caobs> track n 
```
Tell VIS about which antennas are in use, so it only plots those:
```
 vis> array 12345 
```
and check the correlator output looks reasonable:
```
 vis> sel aa,bb 
 vis> sel cc,dd 
```

Set the spectral display program SPD² to show auto-correlations and cross-correlations, plotting the amplitude on all channels, with averaging turned off:

 spd> array 12345         # only show antennae we are using 
 spd> acs                 # show auto-correlations 
 spd> chan                # plot all channels 
 spd> a                   # plot amplitude on the y-axis 
 spd> noavg               # don't average across integration cycles

Adjust the CABB attenuators, by clicking the ATTS "Off" button in the cacor GUI, or issuing the command "atts on". It may take about a minute for the CABB attenuators to adjust to the target rms value of 20. It is likely some CABB attenuators will reach the end of their range (0 or 15) before the rms values are close to 20. In that case, set the mm system attenuators (L is the level of attenuation at each frequency). You should read the attenuators page.
```
 caobs> track n 
 caobs> set mm ca01 L L 
 caobs> set mm ca02 L L   # ...repeat for each antenna... 
```
These attenuators set the receiver output power to the 'C26 splitters'. The output power levels are shown on the MoniCA page Conversion:Freq1_summary. Wait a couple of integration cycles for the readings to settle.
Then let the CABB attenuators adjust themselves again:
```
 caobs> corr atts on      #...wait a couple of cycles, monitor CACOR and VIS... 
 caobs> corr atts off 
```
After a couple of integration cycles, and check the Samplers page in CACOR. A level of around 20 units or less is ok.

You must turn the autoadjustment off once it has settled.
Calibrate the interferometer delays³ (and apply them)
```
 caobs> corr dcal a 
```
You can monitor the progress of this in SPD, by plotting phases for all channels, and by watching the delay plot in VIS. Check all polarisation products. Sometimes it can help to redo the delay calibration after doing a pointing scan.

If you wish you can do a phase calibration as well:
```
 caobs> corr pcal a 
```
To calibrate amplitudes and T_sys values, you will need to do a paddle scan.
Calibrate your amplitudes by measuring the system temperature with a paddle scan (p is the number of the 'paddle' scan in your sched file):
```
 caobs> stop 
 caobs> start p 
```
When the paddle scan is complete, stop the schedule:
```
 caobs> stop 
```
Check your T_sys values as displayed in CACOR look reasonable (at 3mm, about 300K-400K).
Check atmospheric conditions (MoniCA page Environment:Seemon:Summary)
Set up pointing ⁴ with these commands (x is the number of the pointing scan in your schedule file):
```
 caobs> set point_antennas 12345  #which antennas to use
 caobs> set point_ifflag 1234     #which IFs to use
 caobs> set point_pattern 2       #how many correlator cycles in each pointing position
 caobs> start x                   #pointing scan in schedule file 
```
Monitor the progress of the scan in the CATAG window. The pointing type should read UPDATE during this scan. (For other scan types it will normally read OFFSET.)

When the pointing scan is complete, stop the schedule:
```
 caobs> stop 
```
Close the data file to keep the setup data distinct from your source observations.
```
 caobs> corr closefile 
```
Start observations! Don't forget to observe bandpass and flux calibrators at least once during your observation. Also make sure to monitor SPD and VIS to ensure no problems develop during the session.

When finished observing, close the data file and stow the antennae:

 caobs> corr closefile caobs> stow all

Additional Notes

CA01 Focus

At 3mm, the best focus position for antenna 1 is slightly different to all the other antennae. The cause of this is not yet understood.

SPD Setup

SPD has new display commands, you should take the time to become familiar with them.

 spd> acs        # show auto-correlations 
 spd> noacs      # don't show auto-correlations 
 spd> on f1      # show cross-correlations for frequency 1 
 spd> off f1     # don't show cross-correlations for frequency 1 
 spd> on f2      # show cross-correlations for frequency 2 
 spd> off f2     # don't show cross-correlations for frequency 2 
 spd> sel aa     # show the first polarisation product for each displayed frequency 
 spd> sel bb     # show the second polarisation product 
 spd> sel aa,bb  # show both

Cross-correlations are always shown unless you explicitly turn them off.
When showing auto-correlations as well, the 16-panel PGPLOT display often gets filled by the plots for just one frequency. Make a habit of checking which frequency is being displayed.
The polarisation products for frequency 1 are shown on the plots as aa and bb, while those for frequency 2 are shown as cc and dd.

Delays

The delay errors you should expect are now much smaller (thanks to the larger bandwidth of CABB) — typically well under 1 nanosecond.

The value of the CACOR setting delavg has an impact here. delavg is the number of channels the correlator averages together when estimating the delay (by fitting a line to the phase as a function of channel number).

You can find out the value of delavg in (CACOR) like this:

 Command: delavg

You may need to adjust the value of delavg from time to time:

If your delay errors (as viewed in VIS) are flat but far from zero and the phase spectrum (as viewed in SPD) is wrapping rapidly, try:
```
 Command: delavg 1 
```
If your delay errors are very noisy, perhaps the source is not bright enough. It may be worth averaging more channels together:
```
 Command: delavg 16 
```

If you do this, once the delays are calibrated you should set delavg back to the typical value:

 Command: delavg 8

Pointing

While observing with reference pointing you should keep some additional notes. You will need to display the MoniCA page Misc:Pointing

The PNTCOM value - keep a note of this. If the pointing goes bad, this can be used to backtrack to a good pointing solution, you will need this. To use it,
```
 caobs> stop caobs> ppfix [PNTCOM] 
```
It can be useful to note the Last Azimuth and Last Elevation offsets, so you can see what has changed since the last pointing scan.
Finally, keep an eye on the values of the Global Offsets in Azimuth and Elevation. These should not become too large.

More information about reference pointing are given in the pages.

Page developed by: Kate Brooks, Vince McIntyre. Last update 2022-07-06 pge

Observers

Public

Australia Telescope National Facility

3mm ATCA Quick Start

Additional Notes