CACAL

CACAL is a calibration tool that you should use at the start of observations. You do not need to run CACAL again unless:

• you change frequencies;
• a major problem occurs and the delays differ from zero by more than 2ns for continuum observations or 20ns for spectral line observations or 0.5ns for 1934-638.

Before running CACAL, check that the delays are flat.

CACAL calibrates the delays, amplitude and phase for each baseline. The latter two calibrations are not essential, as the offline calibration can deal with them. To use CACAL, perform the following steps:

• Ensure that the Tsys field on CAOBS reads ON. (If not enter CAOBS$>$enable tsys).
• Wait until the array is on source for a strong calibrator (like 1934-638), and the attenuators have adjusted.
• If you have bad interference, use the CACOR command line to select the channels to be loaded as the visibility variables for CACAL and VIS to use. Use tvchans
• Ensure that delays are stable on all baselines and all polarisations.
• Locate a terminal logged on to XBONES.
• Enter the command XBONES$>$cacal.
• Answer A to Automatic or [I] Interactive.
• Check the results with VIS - note that it takes a few cycles for the data to be displayed.

After running CACAL, check that the delays, amplitudes and phases all seem reasonable.

Strong interference can produce a poor calibration. If there is significant interference, you may want to run CACAL on a smaller number of correlator channels.