Flipping Over to Your Competitor?!?

Weirdly, I had a problem I’ve not seen for years crop up recently. And it all started with complaints about car radios flipping between us and a competitor radio station. That’s not a good thing.
Before my guys had even fired up the tuner to look at the RDS transmissions of us and the competitor, I already had a fair idea of what the problem was – mis-configured PI codes.
It’s usually not an issue here in the UK. PI codes for FM broadcast services are assigned by OfCom. You can ask to change them and even get a secondary set of codes for splitting during ad breaks. But let’s take a step back.
A PI code is could be consider a transmitter ID code. It’s 4 character hex value embedded in the RDS data and is not generally seen by end users (unlike the PS name you see on your radio). It’s also surprisingly important and often stored in your radio preset to ensure you’ve tuned to the right station. After all, frequencies are re-used throughout the country, simply tuning the frequency doesn’t guarantee you’ve got the right station.
Now this approach is great for a single transmitter – what about when a station has multiple. The PI codes will be likely different on the transmitters, so how does your radio know they’re part of the same station? Simply, the radio checks the first, third and forth characters of the code match.
As an example, a station could have the codes CC83 and CD83. A radio would consider them as part of the same network. A competitor on CC84 would be considered a different station and your radio won’t switch.
Let’s say the first station mis-configured their code as CD84. At this point radios consider the two different stations part of the same network and in fringe coverage areas, will flip between competitors. Cue complaints from listeners and an odd listening experience driving down the motorway.