When reading data that are all at one frequency, the remaining adverbs can be set to default values. For multi-frequency data, additional steps must be taken. In principle, can process multiple frequencies in the same file, each frequency labeled by a unique FREQID which can be selected in most tasks. However, for book-keeping reasons, each frequency should be saved in a separate file. This can be done in two ways. Adverbs SELBAND and SELFREQ can be specified to choose each frequency separately. This necessitates running FITLD multiple times, one for each frequency. Since digital corrections require computations for every visibility, every channel, and every time stamp, this can result in a lot of extra time reading the data. If one has plenty of disk space, the other alternative is to run FITLD once, saving all frequencies in the same file. Then run the task UVCOP to copy out each FREQID into a separate file. This saves CPU time since FITLD is only run once, but requires a lot of extra disk space since the result is effectively two copies of the same data on disk at the same time.
Before proceeding, the flagging table provided by the online monitoring system at the VLBA stations should be read with the task UVFLG. Little editing of the text file should be required before running this task.