Spectral Line observations with the eVLBI system
NOTE: These are preliminary notes on this observing setup. This is a quite complicated observing mode, so please add information as you find it necessary. It assumes that you have already created a .vex file using
Setting up the eVLBI system
copy your .vex file into /Autocorr
In the v2d file you need to have mode=profile and minSubarray=1 to get it to work with autocorrelation. Also need to set the vex, mjdStart and mjdStop to reflect the experiment name and time of the observations. Also need to either include EOP information which brackets the observations (or edit the dates on the existing EOP information - it isn’t important for autocorrelation data).
Within /Autocorr director
We found that the real time system for hex wasn’t able to keep up with 2×64 MHz with 16384 channels per IF, but it was OK with 8192 (this is set by the spectral bandwidth information in the .v2d file.
Creating the snap file to drive the antenna
Next we need to create .snp and .prc files. Transfer copies of .vex files to firstname.lastname@example.org:/usr2/sched/
run drudg and then specify your .vex file name
Selecting the receiver and frequency setup.
Now VNC into newsmerd so we can setup an easily monitorable observation
Firstly check that no one is using the telescope. Then Navigate to workspace 3 and configure the receiver required in the relevant window
Now in the same workspace configure the oscillators for your observation in the case of my 22 GHz observations of Circinus the required values were as follows
Set the DAS profile
Now we need to vnc onto the Das machine
This machine has a terribly slow vnc connection, you can use ptzhb.phys.utas.edu.au, go to mkv and pan up to view a live feed of the screen.
Now need to change the attenuation, need to move the level as close to the centre for each processor as possible, each dash on level is ~0.5 dBm (higher dBm moves line to the left). To adjust this we use the folly control in workspace 3 on
In the oprin window (on hobart) we can start the schedule running with
Starting the correlator
Back on newsmerd navigate to workspace 5. There should be terminal windows open that noone is using, if not open new ones as you need them.
In one of these windows it is a good idea to check the load on each hex node, can ssh into each node and run top to check each nodes current processing load. If you want to check all at once you can vnc into hex4:5901 and look at the graphs (note:halfway up on the graph is full load), if nothing crazy is going on here continue.
In a terminal on hex0 we need errormon2 running
In another terminal on hex0 we need to start the correlator run.sh holds the commands that you need to run to start the correlator on hex0
In another terminal we want to get the data streaming from the recorder to the correlator.
To start sending the data use the following command, make sure the number after -t (in this case 45m) is changed to your observation time in minutes (m)
At this point the observations should be running. To monitor the observation, keep an eye on the DAS attenuation levels and ra-state live page. Once your observation is complete exit (or ctrl-c) in the vlbi@hovsi and hex0 windows if they don’t close themselves
Then within oprin window
To convert the difx output into a FITS file after the observations are complete navigate to /Autocorr on hex0