@ Chris
The HD radio we Yanks are being bilked with works just fine on FM but is horrible on AM (MW for UK/Euro types). It creates very nasty interference on the adjacent channels, so much so that they can't be heard. It was created by Ibiquity, who is the sole licensed manufacturer, and is in turn owned by the biggies in US broadcasting. So, we listeners get to pay a license fee to the broadcasters for every radio we buy that includes HD.
DAB+ is also known as DRM+ (Digital Radio Mondiale) and is being tested in Germany right now. I have a friend who is the chief engineer at Hesse Radio in Frankfurt, and she is quite thrilled by the shift to digital: saves 90% on the power bill with better service. Their plan is to put the DRM+ transmitters on the FM band, never mind the microwaves that DAB uses, which is a major reason reception is so spotty and short. Any attempt to try to make the original DAB any better is just money down the shite hole. Wholesale conversion to DRM/DAB+ is the only answer, and we Yanks have been sold a bill of goods, so UK listeners beware! The DRM/DRM+/DAB+ standard does not require huge licensing fees either...
Plain old DRM works on MW, LW, and shortwave as well, and does rather well actually. When the ionosphere cooperates, I can listen to stereo from eastern Canada without problems, and I live only 95 miles north of little Billy G. I've heard stations from New Zealand (go All Blacks!), Ecuador, and Euro relays from the Caribbean, all with no fading or interference.
Why (nice) Bill? 'Cuz he retires this week...