SCHED supports observations on telescopes that have VLBA recorders but are controlled through PCFS. This is also done by creating a *.vex file in the VEX format (see section on MkIV).
The telescopes are characterized by DAR = VLBA and RECORDER = VLBA, but CONTROL = VEX. They can have a flexible number of BBCs, and usually have only 2 IF channels: A & C. The telescopes can only be requested to record in any of the VLBA FORMATs.
In addition DAR = VLBA4 and RECORDER = VLBA4 systems have been introduced. These use the flexible VLBA data acquisition rack, but (DAR = VLBA4) have a Mark IV formatter mounted for recording up to 1Gb/s. Note that these systems write Mark IV formatted data and have been created to resemble Mark IV systems. In this sense their name is misleading. These systems required a RECORDER = VLBA4 in the tape era in order to accomodate 2 recording heads (optional), but now all Mark5A systems can record the requisite number of tracks.
Most of the VLBA racks controlled by the field system have what is known as the ``geodetic wiring''. This means that not all of the BBCs can see all IFs. Also, there are not enough sampler inputs do use 2 bit samples from more than the first 8 BBCs. In fact, switching between lots of BBCs at one bit and 8 BBCs at 2 bits requires moving connectors that really weren't designed to be moved often. This is an invitation for trouble. The IF restrictions are such that BBCs 1-8 can see IFs A and C while BBCs 1, 2, and 9-14 can see B and D. SCHED understands these restrictions in it's automatic BBC assignment section. Note that, in some cases, the stations will put the same signals on IFs A and B and on C and D. This can be dealt with in the frequency catalog by giving B as the ALTIFN for A and D as the ALTIFN for C (or visa versa). Or, or course, you can specify IFCHAN explicitly in the setup file.