Mario dei Pintarei wrote:
Hi,
How does HD radio work? I'm an equipment designer (remote control
equipment) from Italy, we don't have it here. Never even heard about it! Is
it Digital? Modulation CODFM? what is the bandwith? Here in Italy we have
DAB... do you have that in the US?

I guess you could say "HD Radio" is the DAB system in the United States.
It is (very!) technically incompatible with the Eureka DAB system used
in Europe. http://www.ibiquity.com .

HD Radio is also known as "IBOC" - "In Band, On Channel". It places
digital carriers in the outer edges of the existing analog signal. (and
for MW IBOC, in the adjacent channels) It offers a "hybrid mode" in
which DAB and analog can be broadcast on the same frequency at the same
time.

All U.S. stations are currently allowed to begin DAB broadcasts at any
time, upon notifying the government. MW stations are only allowed to
broadcast DAB during the day, though nighttime authorization has been
requested. Very few stations are actually using DAB at this time - my
guess would be roughly 50 (most of them VHF/FM) throughout the country.

It is (IMHO) specifically designed to maintain the relative coverage
areas of different stations. (unlike, for example, the Eureka DAB in
Canada where all Montreal DAB stations have equal coverage, regardless
of the coverage of their associated analog stations)
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com