Coming into this discussion late, but I’ll add my experience. I set up my KPC-3 (not +) with APRSIS and could not get KPC and APRSIS to talk. To make a long story short, I had the KPC already in KISS mode before I turned on APRSIS. When APRSIS came up, it would trigger the KPC to go into KISS mode, but instead it was turning off KISS mode. I then learned to put the KPC into simply KISS and it would ignore the command to switch on or off KISS; it just always stayed in KISS.?
