K6JHU said:What is a surprise is the number of AM stations making the transition to HD-2/3. They include KABC, KFWB, and KNX. I will not count 1260 (see my comment above). I also see that KFRG is an HD-2 station. I wonder whether that makes them an LA market station
The reason this didn't happen sooner is that the "HD Alliance" didn't allow it. HD-2 channels were required to offer new formats, which -- needless to say -- attracted little interest because they were thrown together on the cheap. It took a couple of years for overpaid corporate executives of the "Alliance" to figure out that a free market approach would work better, so eventually those restrictions were relaxed. I mean, it only makes sense to put proven AM formats on the FM secondary channels, because AM IBOC doesn't work as claimed, and doesn't fix AM coverage problems (like KYW's null towards Bucks County).
With a slight change in protocol, there might be a way to modify the AM IBOC signal to transmit alternate frequency switching data on the tertiary digital sidebands (the pair which is actually on-channel under the analog sidebands) and eliminate the primary and secondary sidebands which cause adjacent-channel interference. Wouldn't that be a relief?
Like RDS, this data would allow receivers to automatically find the simulcast FM channel (whether HD-1, HD-2, analog full service FM, or translator), or to an internet stream. But as I mentioned yesterday, existing HD receivers can't be upgraded with new firmware to support such a feature, so it would take many more years to implement it.