I bet the firmware has a logic 1 to PTT_P output cell instead of logic 0. ? To get pulled all the way up to 5v, the STM32F IO cell for PTT_P must be in tristate mode. To go low, the firmware turns on the totem pole output, allowing what should be the logic 0 to get through and driving Q102's gate to ground. Instead it is a logic 1 going out, driving PTT_P from VDD at about 3.3v. ? Your best bet might be to somehow use PTT_N with a bit of extra circuitry out at the amp to invert it. ? Jerry, KE7ER ?
