You just create a custom scan list and select channels from any system. You do NOT include any control channels in this list. You are not entering frequencies into the custom scan list, only selecting from the pool of channels already in any system (sets assigned to systems). This scan list can then be assigned to any system.
When assigned to a trunked system, trunked TGs, as well as conventional P25 and analog channels are scanned. When assigned to a conventional system, trunked channels are skipped.
-B