I will try to get some PLC experts to provide you a response soon.
PLT_Start() configures the PLT in receiver mode by default.
When you are using the PLT module in FSK Modem mode you can switch to the transmitter mode by using PLT_SwitchToTransmitter() and back to receiver mode with PLT_SwitchToReceiver(). To transmit data in FSK Modem mode use PLT_SendData().
When the PLT module is used with the network protocol Use PLT_SendMsg() to prepare the message to be transmitted followed by PLT_Poll() to send the message.