The referee wears a microphone and a transmitter, combined with and controlled by an evaluating unit, constantly operating and picking up all sounds and tones that are then digitised and analysed to recognise the tones (or trills) of the referee's whistle, according to a bit pattern in memory. This switches on the transmitter and it is also switched off after a delay. The total pattern is passed to the central receiver. The central receiver sends the whistle pattern to loudspeakers in the stadium, to an internal area and also to the television terminals and video recording.
