Radio to TNC Connection Audio Modulation. When connecting to the speaker or headphone jack, the Receive Signal wire is connected to the tip of the plug. For this type of connection, many TNC manufacturers provide a pre-wired cable.
Some radios have a pin on the mic jack for the receive signal.
The Receive Signal wire may be connected to this pin. Other radios provide a similar connection on an auxiliary jack. DFSK Modulated signals need to come directly from the discriminator of the radio and not through the audio circuits of a voice radio. Some radios may provide this signal at a data-connector pin. If this pin is not provided, the radio must be modified to connect the Receive Signal wire directly to the discriminator output.