Roberts Radio Gemini 21 RD-21 - Manual (Page 14)

Active station
When this setting is switched on the display will show only those that a
signal can be found for.
Prune stations
Some DAB services may stop broadcasting or you may not be able to
receive a station. Prune stations will delete the DAB stations from your
station list that can no longer be received.
When this feature is selected your radio will delete the stations that are
not currently being received.
13