As broadcasters increase the use of FM translators for re-broadcast of AM stations as well as HD2 and HD3 multicast channels, many have opted to include Radio Data System (RDS) data subcarriers on these transmissions to cater to the ever-increasing pool of receivers that have text displays and support RDS technology to display song title, artist, station branding, format information, and offer song tagging. With the continuing rise of these translator stations, and also with increased adoption of RDS on full-power FM stations, a problem can develop if these stations are not diligent in properly configuring their RDS encoders.

One of the most important parameters that needs to be set in an RDS encoder is called Program Identification (PI), a four-character hexadecimal value that uniquely describes a station to RDS-enabled radios. Some advanced radios use the PI code to identify any simulcasts available on alternate frequencies in the same market (this feature is more widely used outside of the US). In an ideal world, a set of stations that are perfectly time aligned airing identical programming at all times could duplicate the PI code across their frequencies to enable such advanced receivers to switch to the frequency with the best signal. Broadcasters need to make sure that if their FM station, whether a full-power FM or an FM translator, has the RDS subcarrier, that the PI code is properly configured to ensure that advanced radios cannot mistakenly auto-tune to other stations in the market with different programming.

Anecdotal reports suggest that many broadcasters, when installing RDS encoders, take them out of the box and place them on the air with minimal configuration, resulting in transmission of a factory default PI code. Then, when a second station in the market duplicates the same mistake, the same PI code ends up being broadcast on multiple, unrelated stations. Advanced receivers can then execute seemingly random jumping from station to station.  In some cases, listeners have taken cars back to dealerships reporting radio problems, or in some cases reported the issue to one of the stations on which the inadvertent switching was occurring.

In another case, an HD2 multicast channel was simulcast on an analog FM translator and the local engineering staff, with good intentions, selected the same PI code as used on the multicast channel’s FM host station. The issue here was that the same PI code was now duplicated on two stations in the market that had different programming, so an advanced receiver might mistakenly execute automatic switching between the two stations.

In a third case, a radio station (“station 1”) had an auxiliary transmitter site and an auxiliary RDS encoder which was installed but with the factory default PI code.  Under normal circumstances, station 1’s primary transmitter site was used and the primary RDS encoder was configured with a proper, unique RDS PI code for the market. But, when the backup site was needed, the auxiliary site RDS encoder was sending out a factory default PI code. A second station (“station 2”) in the same market had its primary RDS encoder set to the factory default code as well. This led to a lot of confusion, as on some days radios were randomly jumping between two dissimilar stations, but some days this would not occur. It took some time to determine the issue only occurred when station 1’s auxiliary site was called into service, and that the auxiliary site had a misconfigured auxiliary RDS encoder. Upon learning of the error, both the auxiliary RDS encoder for station 1, and the primary RDS encoder for station 2 were corrected.

The best way for broadcasters to avoid these problems is to make sure each FM station with RDS has a unique RDS PI code in use, for both the station’s market as well as any adjacent markets that could be receivable on the edge of the station’s coverage. A good reference document discussing the setting and use of PI codes is the National Radio Systems Committee’s (NRSC’s) RDS Usage Guideline, NRSC-G300-B. Section 5.1 of this document discusses the practical use of PI codes in great detail, and can guide stations on how to properly set the PI code on each of their stations.

NRSC-G300-B cover

For full-power FM stations, the “call letter conversion” encoding method is used to establish the proper PI code setting, discussed in Section 5.1 of G300-B, and more fully in the NRSC’s RBDS Standard document NRSC-4-B, Section D.7.1. It is noted here that not all stations can use this method, in particular if they are using RDS-TMC based traffic services. This call letter conversion method will not work for FM translators airing AM or HD2, HD3 programming. Section 5.1.1 of G300-B discusses several options broadcasters can consider to ensure they have a unique PI code in use on their translator-based stations.

In summary, having a unique PI code on each FM station, whether full-power or translator, is a very important configuration item that broadcasters must not overlook. The NRSC-G300-B RDS Usage Guideline and NRSC-4-B RBDS Standard are important and useful references that can help broadcasters understand this technology and configure their equipment properly.

Thanks to Alan Jurison, Senior Operations Engineer with iHeartMedia and chair of the NRSC’s RDS Usage Working Group, for his contributions to this article.