traffic announcement flag
The announcement identifier(DK) is an identification signal from the ARI information that is switched on when traffic news is announced.
For announcement identification, the 57 kHz station identification subcarrier( SK) is amplitude modulated with a 125 Hz signal.
The paging signal triggers the identifier tone, which is broadcast before the traffic messages on VHF broadcasting, and causes the switchover from normal VHF broadcasting to traffic broadcasting. The DK frequency of 125 Hz is derived from the 19 kHz frequency of the pilot tone via frequency division.