The Yaesu FT-450D works well with the NinoTNC but requires an audio isolation interface between the TNC and the radio, since it doesn't like sharing a ground with the TNC / PC, at least in my setup.

Bring 5V out of the NinoTNC on DB9 pin 7 using a bodge wire.

Connect DB9 pin 7 to the relay coil, and the other side of the relay coil to DB9 pin 3, the PTT pin. When the NinoTNC keys up the radio, the PTT pin is grounded, creating a circuit between +5V and ground, energising the relay coil.

Run the TX and RX audio pins from the DB9 through standard audio transformers.

Connect as normal on the radio side.