Criticisms of problems in using HD Radio encodings for AM stations date back to the earliest days of the technology: The FCC approved nighttime broadcasting of HD Radio over AM a few months ago, but there are still relatively few AM stations using HD Radio, and thus problems are only starting to emerge.
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Radio World reports that Citadel Broadcasting, which has HD Radio enabled on 16 of its 66 AM stations, decided to turn off the 10 stations that were broadcasting digital signals at night due to reports of interference. The problem occurs when listeners hear “hiss” and stations on nearby channels hear noise.
I first heard of this problem a couple of years ago while sitting in on a talk at the AES convention in NYC.
26 October 2007 at 6:02
“ABC Citadel suspends AM IBOC”
“The order, effective immediately, is reportedly for all Citadel AMs running IBOC at night. While no reason was given for the order, it is believed that interference issues are the most likely factor.”
http://www.orbitcast.com/archives/abc-citadel-suspends-am-iboc.html
“AM Broadcasters Back Away from HD Deployment”
“This is a major setback for the adoption of HD Radio, especially on the AM dial, and Citadel is the first large broadcast conglomerate to back away from full deployment of the HD broadcast technology. Although the company’s gone out of its way not to characterize its move an indictment of iBiquity’s proprietary digital broadcast standard, the problems with AM HD broadcast interference are well-known and -documented.”
http://diymedia.net/archive/1007.htm#101307
“Left in the dark”
“Local ratings show that plenty of Pocono listeners tune in to AM 770. But about two weeks ago, WABC radio became impossible to hear in the Poconos after sundown. And although the daytime signal is still strong, WABC it is not likely to he heard here in the dark again. What happened. An advancement in broadcast technology. WABC flipped the switch for HD Radio. Something many stations are doing with, so far, little notice from the public.”
http://www.poconorecord.com/apps/pbcs.dll/article?AID=/20071001/LOCALENT/710010324
“Night of the Bees”
“Radio listeners across America are trying to hide from a monster, but there is no shelter. After spending its adolescence in technical trials during daytime hours, IBOC has now come out at night… For example, in New York City, WOR broadcasts on 710 kilohertz. When it turns on its IBOC equipment, the digital noise it produces can be heard on 690, 700, 720 and 730 kilohertz with a reduced fidelity analog audio signal remaining on 710…”
http://karlzuk.blogspot.com/2007/09/night-of-bees.html
“AM HD Radio 24 x7 as of September 14, 2007″
“The HD Radio Interference, we will coin it HDRI, is characterized as a loud obnoxious frying egg noise on top of an AM radio station’s analog signal. Here at PopularWireless HQ the kitchen is open and the eggs are cooking big time. A favorite here has been New York’s famous WABC where many enjoy listening to Coast-to-Coast AM in the early mornings. WABC is now plagued by HDRI making listening impossible at times. Across the AM dial the analog receiver is sizzling away.”
http://www.popularwireless.com/blog1/2007/09/22/hd-radio-24-x7-as-of-september-14-2007/
“Digital Signals Spark Static From AM Radio”
“A growing number of radio listeners are encountering similar interference — hisses, whistles or static — on their favorite AM stations. The problem for WTRI began about a year ago, when Bonneville International Corp.’s WTOP, the AM station at 1500, began using a digital signal that interfered with WTRI’s analog signal in some broadcast areas. It’s one of the unexpected consequences of the radio industry’s transition to digital broadcasts.”
http://online.wsj.com/public/article/SB114125971438087021-05D89puCE5WSP_r8GSeoRd_7fCE_20070301.html?mod=rss_free