hubcity said:
Me, I've got cognitive dissonance going for me now - I do think the radio's pretty good. I can also think of lots of ways the service can be improved, though, and it really does seem as though this was a compromise. HD2 and HD3s should be receivable, solidly, in the entire service area of the original FM signal, and I'm surprised broadcasters settled for anything less.
You are correct, it is a compromise. I think most knowledgeable engineers anticipated problems with an in-band hybrid approach. When the system was originally designed, there were no plans to offer HD-2 or HD-3 services. The only audio channel was to have been "HD-1" with the FM analog serving as a backup, so there was less concern at that time about digital signal dropouts.
As I recall, the "big guys" in commercial radio who demanded this system (rather than an out of band approach) actually didn't want any improvement in coverage -- they wanted to maintain the status quo, not to level the playing field. They owned the beachfront property and didn't want the little guys getting a leg up. They seemed to think ancillary data would be IBOC's killer app -- for example, stock quotes, sports scores, traffic, etc. I remember reading an article about "bits for bucks"; how we were all going to make big money selling data services. Yeah, right.
NPR came up with the idea of providing secondary audio channels. As you probably know, many public stations split their formats between classical music, news, jazz and other niche offerings, so NPR saw multicasting as a way to keep most everyone happy most of the time. Then it dawned on the big guys that their listeners wouldn't spend money on new receivers to hear the same programming that was already available in analog, so most of the commercial groups decided to go along with the multicasting idea. But of them few knew what to offer that would avoid diluting the audience of the main channel. This may explain why more of them are now offering simulcasts of their co-owned AM stations.
The problem with turning up the digital power above one percent is that this will violate the recognized occupied bandwidth rules and spill over into adjacent channels. Again, I suspect most engineers know this will cause trouble, but they must answer to superiors who are getting desperate.