Re: CC Skywave for Christmas
I'm not an expert on the topic, but here's a summary of the current terrestrial digital system in the U.S.
Not many AM radio stations are broadcasting a digital signal. Digital has proved not to perform very well on AM, especially for lower power radio stations, so most AM radio stations with a power of 5 kW or less are analog-only. The combination of increased noise in the AM broadcast band along with nighttime skywave interference have limited the viability of digital on AM. Digital has been much more widely implemented on FM.
HD digital (not the same as DRM or DAB) is what's offered on AM and FM in the U.S. (and a few other nations). The current system is "hybrid" analog and digital sharing the same carrier frequency. HD digital is primarily available in car receivers. Very few HD receivers are available for tabletop or portable use. Insignia, the Best Buy store brand, was an early adopter. Here's an example of an Insignia HD digital receiver currently available... http://www.bestbuy.com/site/insignia-hd-radio-tabletop-radio-black/4635744.p?id=1218505477073
The HD digital hardware and software design is proprietary, initially introduced by iBiquity, but another company recently purchased iBiquity (I forget what company). Anyway, the proprietary design has harmed its introduction because both manufacturers and broadcasters must pay a fee to obtain rights to use HD digital.