FEFILTER specifies the VLA front end filter. Some options are: '0000' - 50 MHz. '1111' - 25 MHz. '2222' - 12.5 MHz. These are used to help avoid RFI especially at the lower frequencies. They are centered or close to the normal 50-MHz band. Anyone using these should understand the VLA system well.
Note that, if any of FLUKEA, FLUKEB, VLAFEAB, VLAFECD, VLASYNA, VLASYNB, VLAIF, FEFILTER, or VLAROT are specified, both LO and FI cards will be made. In such cases, any other parameters allowed to default will be set to the standard value for the specified VLABAND.