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It is commercially known as the iBiquity In-Band-On-Channel (IBOC) system a.k.a. HD Radio, now owned by DTS. It has been implemented in the North American FM ra

It is commercially known as the iBiquity In-Band-On-Channel (IBOC) system a.k.a. HD Radio, now owned by DTS. It has been implemented in the North American FM radio band and features multiplexing of 2 or more subchannels per station. It has been introduced in the AM band as well but a variety of technical issues have tended to be too problematic. Unlike DAB, which has its own dedicated bandwith, HD Radio is a system of sharing an analogue FM radio station's existing bandwidth with a slice of digital payload. HD Radio-capable receivers pick up the analogue signal as usual, and if the digital streams are viable will switch to reproducing them for the listener. HD Radio can be broadcast digital-only, but I'm not personally up-to-date on any presently doing that, given all the legacy analogue FM receivers out there.

argilo 3y ago
I'm not aware of any digital-only FM stations either. But there are a handful of digital-only AM stations, like WWFD.
psim1 3y ago
> if the digital streams are viable will switch to reproducing them for the listener. This produces a weird effect when listening in the car and moving in-and-out of good digital SNR range. When the radio switches between analog and digital, unless the station has them perfectly synced (never), there's always a little echo or stutter. It seems like it would be nothing but it's quite annoying.
- wkat4242 3y ago
  It shouldn't be impossible to sync. Here in Europe we even sync FM transmitters so they can broadcast on the exact same frequency without causing interference! That requires a magnitude higher precision than this.
- cf100clunk 3y ago
  Particularly annoying while driving in very hilly areas, that's for sure. There are some traits of signal propogation that are very difficult to work around, even with buffering and error correction remedies.
wkat4242 3y ago
Hmm that doesn't sound like a bad option at all. Here in Europe we're trying to displace FM by DAB+ and it works really crap because the coverage of DAB is worse. Having fallback to analog would really help to cover the gaps. However the EU seems hell-bent on freeing the 87-108 spectrum so that they can sell it. Just like they did with the analog TV bands. Its 700Mhz band is now one of our cell bands. Of course the continued ubiquity of FM receivers makes this a bone-headed plan but sadly they have many of those right now, like chat control.

argilo 3y ago

I'm not aware of any digital-only FM stations either. But there are a handful of digital-only AM stations, like WWFD.

psim1 3y ago

> if the digital streams are viable will switch to reproducing them for the listener. This produces a weird effect when listening in the car and moving in-and-out of good digital SNR range. When the radio switches between analog and digital, unless the station has them perfectly synced (never), there's always a little echo or stutter. It seems like it would be nothing but it's quite annoying.

wkat4242 3y ago
It shouldn't be impossible to sync. Here in Europe we even sync FM transmitters so they can broadcast on the exact same frequency without causing interference! That requires a magnitude higher precision than this.
cf100clunk 3y ago
Particularly annoying while driving in very hilly areas, that's for sure. There are some traits of signal propogation that are very difficult to work around, even with buffering and error correction remedies.

wkat4242 3y ago

Hmm that doesn't sound like a bad option at all. Here in Europe we're trying to displace FM by DAB+ and it works really crap because the coverage of DAB is worse. Having fallback to analog would really help to cover the gaps. However the EU seems hell-bent on freeing the 87-108 spectrum so that they can sell it. Just like they did with the analog TV bands. Its 700Mhz band is now one of our cell bands. Of course the continued ubiquity of FM receivers makes this a bone-headed plan but sadly they have many of those right now, like chat control.