Hi, I mis-typed: "the "Transceiver QSK line"; turns out this is just the usual coax from the transceiver to the linear,..." No so, it is the usual amplifier relay line from transceiver to linear that he calls the "transceiver QSK line." In two of the connection options (transceiver dependant) this line goes to the QSK-5 "Key 2" input sense socket. 73, Jim KH7M