C.10 Incorporating non-VLBA antennas

Many non-VLBA telescopes have their amplitude calibration incorporated in the tables loaded by FITLD. We retain the following sections for the case where some telescopes are not included in calibration tables for whatever reason.

The phased-EVLA came on-line in February 2013. Its calibration is very different from the old VLA. With the phased-EVLA either an ANTAB style file was provided to the observer or the calibration information is attached to the data. This calibration is generated from the switched power measurements attached to the EVLA only data. There is no need for special calibration steps. However, the observer may wish to improve the calibration by editing the switched power and recreating the ANTAB style file. More information on this can be found in 9.5.2.4. There is a separate section (C.11) dealing with pre-EVLA VLA data.

C.10.1 Loading Tsys and Gain Curves

Most telescopes that do not have Tsys and gain curve information attached to the data will provide the user with a text ANTAB format file that can be loaded with ANTAB. Please see EXPLAIN ANTAB for more information on the ANTAB format. Follow the steps below to load calibration information and amplitude calibrate the data.

  1.  To prevent any chance of having to re-run FITLD, first save the VLBA TY and GC (and all your other) tables by running TASAV. Then run ANTAB with CALIN set to the ANTAB file and setting TYVER and GCVER to the highest numbered tables (usually 1). You don’t want to leave TYVER and GCVER equal to 0 because that causes ANTAB to creat new TY and GC tables with only the antennas in the file you are loading. If ANTAB fails, it is most likely caused by the input file not being formated correctly. Perhaps you needed to add an INDEX entry or the file wasn’t in true ANTAB format. Also, if ANTAB fails check that the TY and GC tables have not been corrupted. If they have you should delete the tables and copy the original tables from the TASAV’ed file with TACOP.
  2.  Now, run VLBAAMP as described in C.7 to combine the gain and system temperature information for all antennas into the appropriate SN and CL tables. Then, use SNPLT or VLBASNPL as described in C.7 to make sure that the resulting SN now contains amplitude calibration for all the antennas and IFs included in the project.

C.10.2 Pointing Flags

The VLA, GBT, AR and possibly other telescope’s on-line systems produce only recorder-related flags, not pointing flags. Thus, for example, there are no flags for when the telescope is not on-source. This can lead to a large amount of bad data especially if you are changing source frequently. However, the VLBI scheduling program SCHED creates a *.flag file which contains estimates of how long it takes these antennas to slew. The *.flag file will also contain flags for all antennas in the experiment, so it is best to remove the flags that pertain to the VLBA antennas. The flag file can be read in with UVFLG using the INTEXT adverb.