Steven Universe: Unleash the Light

The mysterious radio signal is located in Pyrope's World, 3-4.  From the entrance, go right for a cutscene, and the signal will move.  Go to the Alien Moon boss stage next, and go to the end of the stage.  You will finally be able to recruit Peridot into your team, before being whisked off to the newly-created 1-10.  The trophy will unlock after a cutscene at the end of the stage.

The radio signal quest will eat into your completion percentage; hence, it is required for Perfect Porkchop .