The invention relates to a method and a system for external, digital coding of a baseband or intermediate-frequency signal. Initially, a digital datastream is converted in a coding device into a digital-baseband signal in the time domain or into a digital intermediate-frequency signal in the time domain. The digitally generated signal is output via an asynchronous-serial interface of the coding device to another device. Such a device also provides an asynchronous-serial interface, which is connected to the asynchronous-serial interface of the coding device. The device reads in the output digital-baseband signal or intermediate-frequency signal for further processing.