COMMAND NAME:	frequencies

TYPE:		Data selection

SYNTAX:		"frequencies XS, C"

DESCRIPTION:

Enters a list of allowed frequencies into the inputs.  All alphabetic
characters are accepted, in any order, lower or upper case, with or
without spaces or commas.  Duplicate characters are ignored.  Scans
which involve frequencies not in this list will fail the filter tests
applied by edit inputs, read, and plot.  Typing "frequencies" without
arguments removes any limitations on frequencies.