Complex sentence: Upon hearing the break-in signal the interrupted station simply stops sending and transmits a single "K" prosign indicating for that the interrupting party may go ahead and then the interrupted party listens for the interrupting party to make their own transmission.
Split into simpler sentences: Upon hearing the break-in signal the interrupted station simply stops sending and transmits a single "K" prosign indicating that the interrupting party may go ahead. Subsequently the interrupted party listens for the interrupting party to make their own transmission.