Autofahrer-Rundfunk-Informationssystem

Autofahrer-Rundfunk-Informationssystem (ARI, German for: Automotive-Driver's-Broadcasting-Information) was a system for indicating the presence of traffic information in FM broadcasts used by the German ARD network of FM radio stations from 1974. Developed jointly by IRT and Blaupunkt, it indicated the presence of traffic announcements through manipulation of the 57kHz subcarrier of the station's FM signal.

ARI was rendered obsolete by the more modern Radio Data System and the ARD stopped broadcasting ARI signals on March 1, 2005.

The SK signal is actually the 57 kHz subcarrier that is transmitted by the ARI-compliant FM station for this functionality. This frequency, like the RDS subcarrier frequency is chosen because it is the third harmonic of the 19 kHz pilot tone used in the FM-stereo transmission standard. An easy way to understand that is that this frequency is the 19 kHz pilot tone multiplied by 3.

An ARI-equipped radio would illuminate an indicator lamp to show that this function was in force. Most such radios would use this function further to help users search for ARI broadcasts. In the Radio Data System environment, the TP signal is equivalent to this basic function.

The basic method implemented on an analog receiver would be a switch usually marked SDK or VF. Radios that used the "classic" mechanical push-button preset system would have one of these buttons set aside as the VF switch. If this switch was on, the radio would mute unless it was tuned into a station that transmitted this signal.

If the radio was a digitally-tuned receiver, this switch usually engaged an "ARI-seek" mode which had the radio seek for any ARI station if it was out of range of the currently-tuned ARI station.

This function, which is superseded by the RDS TA function, was tied in with the broadcasting studio and would be triggered whenever the traffic-announcement jingle was played. A 125 Hz tone would be modulated on the 57 kHz ARI subcarrier tone while this was happening.

A radio that used a "DK" switch, often part of the "SDK" or "VF" switch, was placed into "traffic-priority" mode. It would pick up on this signal and come out of a muted state or cut over a tape or CD that was playing and play the announcement at a fixed volume level.

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