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 §18.104.22.168. There is a separate section (§C.11) dealing with pre-EVLA VLA data.
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.
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.