A few years back I presented an essay at the SWLFest titled "Whatever Happened to Digital Radio?" The gist of it was that Digital Radio was already on the decline in the US having failed to gain any market traction. The story is the same worldwide on shortwave too.
Unlike other markets around the globe the US uses a product from Ibiquity called In Band On Channel. Ibiquity has been bought and sold a few times since the release of IBOC. Its product name was made a little more friendly by the phrase "HD Radio" giving the illusion that the audio quality was superior to the existing traditional AM and FM systems
Over time the IBOC system gained the nickname "It Buggers Other Channels". It's easy to see why. Take a look at the below screenshot taken from my SDR software. I have an Afedri SDR-Net connected to a MLB-30 active loop antenna. I spotted this signal while looking for something else.
It's 30KHz wide!! AM stations in the US are normally placed into a 10KHz slot. There is a vacant 10KHz slot either side of them (called "guard channels") which are usually reserved for stations in other markets thus allowing a kind of jigsaw puzzle whereby the various markets fit into each other without interference.
So a signal 30KHz wide would invade both the guard channels on either side of the allotted frequency. The IBOC signal is injected in "wrapper" mode whereby the digital data is sent in 2 carriers either side of the main AM signal. In the above picture an AM carrier can clearly be seen in the right hand data bundle (the square thing to the right of the red line). Listeners to the station on buried by the data signal will hear a rushing noise along with their normal station.
Perhaps this interference is why IBOC is on the decline? Its the same story on the FM band too. A scan of my local AM band (15 miles NW of Philly) reveals just 3 stations using IBOC down from 15 just a few years ago.
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