Not sure that I understand what you are asking for the BITX40, as there is not a Q74 in that rig.? If your question is for the uBITX (any version), the T/R signal that controls the gate of Q74 is a 5 volt signal direct from the Raduino board.? It is labeled T/R, not TX/RX.? It is also connected to Q15 that then drives the K1 relay.
73
Evan
AC9TU
