1. Data editing and flagging
Due to the poor stability of the instrument, it had been seen that phase jumps sometimes occurred on one of the receivers. If such jumps occurred often during the period of an observation, this technique would not work. It would be wise to stop proceeding to the phase transfer process. If only few bad points seen in phase from one of the receivers, please flag the data for both receivers and try the phase transfer technique following the procedure described below.
2. Linear regression of the phases between 230 and 690 GHz
The observation must include a source which is strong enough at both 230 and 690 GHz so that it can be used to determine the phase correlation between 230 and 690 GHz. Observing scans of the source must be interleaved with other sources in the observing track, covering a time range as large as possible. Here we assume that the small planet Ceres was used in the observation. Please follow the detailed procedure discussed in Chapter 2 to perform the linear regression of the phases between 230 and 690 GHz.
Task varfit with options=phareg gives the linear regression of the phases between 230 and 690 GHz. Bad data points due to the instrumental defects (such as phase jumps) might ruin the linear correlation. If only few bad points, then one might go back to flag the data and run selfcal again until one is satisfied with the linear correlations on each of the antennas fitted using varfit:
varfit vis=ceres.221.lsb,ceres.682.lsb xaxis=time yaxis=phase \ device=/xs nxy=2,3 refant=6 options=phareg
Please keep in mind that the slope table, containing the fitted slope and phase offsets for each antenna, is saved in ceres.682.lsb, which will be used in the phase transfer later.