A AV-4312 RF modulator. Which converters your any Pal video source that can be connected via the standard AV (composite) plug to RF (attenna) plug.
This conversion is called modulation, your video and audio signals are combined and modulated to a specific frequency much like free to air tv is. So to pick up the signal you only need to tune your tv or vcr, etc to that specific frequency in this case 57.25MHz which is best to be tuned onto channel 1 of your tv or select device.
The box is capable of 3 inputs, the input displayed is selectable through push buttons on the front of the unit, much like a switch box. You can also input your standard atenna in to the box and tune in the tv channels as normal to avoid constantly changes cables.