BBC is used to specify the Base Band Converter (BBC) to which each baseband channel is assigned. A value can be given for every channel. If any or all values are missing, SCHED will try to set to reasonable default values for the digital backends and VLBA and MKIV format observations. This is the option most users should take.
Note that BBC assignments are arbitrary for the RDBE and the old VLBA systems since all BBCs can see all input IFs. However, for Mark III and Mark IV systems and the current version of the DBBC, there are strong constraints. For Mark III/IV ``astronomical patching'', which is the only one currently properly understood, the odd BBCs must be connected to IF1 (IFCHAN 1N or 1A where 1N is normally LCP and 1A is normally RCP). Even BBCs must be connected to IF2 (IFCHAN 2N or 2A, where 2N is normally RCP and 2A is normally LCP). Mark III/IV ``geodetic patching'' is more complicated and partially understood by SCHED. Essentially IF1 is connected to BBCs 1 to 8, and IF2 is connected to BBCs 9-14, though in some systems there is an IF3 available on BBCs 3 and 4 (this is actually an additional mixer on IF1 allowing access to a wider range of frequencies). The current version of the DBBC also has constraints on patching of BBCs to IF as described in the DBBCVER section of the manual.