The data was largely clean but could sometime suffer from scintillations and intermittent radio frequency interference (RFI). In addition to normal editing of the data, the scintillations affected data and channels affected due to RFI were identified using the tasks POSSM & TVFLG and the affected data was edited.
Further, we deleted the SN (ver 1) and CL (ver 2) tables, and the task CALIB was run using the settings: SOLINT=0.1; CALSOURCE= ' '; SMODEL 1 0 0; SOLMODEL = 'A&P'. SMODEL 1 0 0, was used for specifying to use a source model using flux density, SOLINT=0.1 was used for keeping the the solution interval to 0.1 min and solutions were derived by using all the sources. The task GETJY was run to derive the flux density of the target sources (which was assumed as a secondary calibrator).
The task GETJY was run using: CALSOURCE='3C286', '3C48', '3C147', '' and SOURCE=''. The derived value of the flux density should have an error less than 10%. and then the task CLCAL was run for all the sources.
Channel averaging Channel averaging is done to reduce data volume and to increase signal-to-noise (snr) ratio. Also while doing averaging, if the RF band is split into frequency channels which smaller channel width the effect of bandwidth smearing can be reduced. This was done by the task SPLAT which used to apply the time and bandpass calibration (the CL and BP tables respectively) to the data before channel averaging and a calibrated database generated was generated in the following manner: DOCALIB=1; APARM(1)=1; DOBAND=1;ICHANSEL=5, 115, 1; SOLINT=0. APARM(1)=1 is for averaging frequency channel selected by ICHANSEL will be averaged in the output, DOCAL=1 is to apply calibration, DOBAND=1 is to correct the bandpass before averaging and SOLINT=0 is for no time averaging of the data.
This produces visibility data averaged to single channel file in case of 610 MHz. As usual, the task INDXR was run to obtain NX, etc. tables.
The central channels were averaged using AIPS task SPLAT to reduce the data volume and to increase the signal-to-noise (snr) ratio.