John Limpert wrote: > Many AM stations have to shutdown at night. Good point. So I wonder exactly what the FCC means by "Authorizes AM nighttime operations." Do they mean that now all AM stations are allowed to continue at night? Or do they mean that *digital* over the AM band is allowed to continue at night? > Wasn't there a restriction against nighttime AM digital operation, > as it hadn't been properly tested for those propagation modes > (skywave) and the effects on other stations were unknown. It's the simple fact that in hybrid mode, each AM station with digital simulcast takes up 30 KHz of spectrum. So at night especially, each digital station in the AM band will clobber two other AM stations that might be in that slice of spectrum, for quite a long distance. If the station transmits only in digital, then the IBOC scheme has an option where the station crunches down all of its signal in the same 10 KHz bandwidth that is now given to regular AM. So nighttime operations could presumably be the same as they were in the analog-only days. This is different from the FM band, in which stations retain their entire 400 KHz of channel width even if they are all-digital. Bert ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.