Ok, I think this was a classic case of "Mission Accomplished" when it wasn't actually.
Terminal successfully tells me that FULLDUP is on on, however, I cannot get full duplex TNC activity during a Falconsat pass. While my B band is decoding packets on the downlink, I cannot send beacons or messages on the uplink A band.
What I have to do to FORCE the transmit is to tune the Rx band down 5 to 10 kHz so that the TNC no longer sees packets - then there will be a flurry of Tx activity, then I quickly tune Rx band back to the proper frequency to resume decoding the downlink.
So is the only way to interface with the TNC when it is "PACKET12" mode? I tried to switch the TNC to "APRS96" mode (which is what is needed for falconsat), and then you cannot send commands via the com port (behaves just like the TNC is off).
DCD sense is currently set to "Ignore".