A proposal of a traffic information signalling compatible with AM-MF broadcasting

The possibilities for information signaling through two additional tones, coherent with the usual AM stereo pilot tone used in the present USA AM stereo systems, are investigated. Two criteria are defined: an objective one, based on US Federal Communications Commission rules, and a subjective one, based on average human audio perception levels. On the basis of these criteria, the width of the injection gap (to inject desired two tones) is evaluated. The signaling method includes two signals besides the pilot tone: one for program identification and the other for message-in-progress. The primary intention of the signaling is coupled to the traffic radio information service, but without any modification the proposed system could be used for other purposes (paging, alert signaling, exact time distribution, etc.)