Functionality

1. ✓Microphone input : tested with RSP1A
2. ✓Speaker : tested by tuning to FM broadcast band
3. ✓Programming : tested with Chirp
4. TNC connection :
   1. ✓PC receiving audio : correct volume setting of the radio is crucial.  Use audacity to tune the volume knob to avoid over-steering the laptop's audio input.
   2. ✓PC sending audio : PC volume must be adjusted here as well.
   3. ✓Pulling CN6.5 to GND enables the transmitter

So all functionality works as expected!