HD Radio: AM-HD
"FCC Tunes Into HD Radio--May Turn Off Distant AM"
"But HD Radio AM broadcasts may also obstruct one of AM radio's oldest attractions--so-called skywave reception, in which AM signals bounce off the ionosphere after sunset and allow listeners to tune in from hundreds of miles away. For example, two years ago, a Cleveland station's broadcast of an Indians game kept me entertained on the New Jersey Turnpike; a couple of nights later, I tuned into WTWP-AM's coverage of a Nationals game in north Jersey. A nearby HD AM (I realize this sounds like an oxymoron) signal, however, can interfere with a distant analog signal if the two stations are adjacent on the dial. For instance, a Jersey station's digital broadcast on 1510 or 1490 AM might have stopped me from getting WTWP's analog signal at 1500 AM."
"Statement of Jeff Littlejohn SVP Engineering Clear Channel"
"The current AM allocation rules require Co-Channel stations to provide 20:1 protections to each other and first adjacent channel stations to provide 2:1 protection to each other. While this works fine in an all-analog environment, it does not seem to be sufficient in the presence of IBOC. The energy above 10 KHz from the proposed Hybrid IBOC signal significantly exceeds the energy present in the current analog AM signal. For this reason, the amount of energy provided to a first adjacent station is significantly more detrimental than our current allocation rules allow for."
"AM Broadcasters Back Away from HD Deployment"
"According to a leaked memorandum from ABC/Citadel's executive chief engineer, all AM stations in the company's stable have ceased broadcasting in digital at night, effective immediately. The memorandum does not give specifics, but follow-on reports cite interference between AM stations on adjacent channels as a major factor for the decision. Interestingly, some suggest Citadel executives knew such a problem might be in the offing, but they went ahead and turned on their digital signals at night anyway."
"Pistons Moved to CBS Due to HD Radio Interference"
"Pete Skorich, Detroit Pistons Director of Broadcasting, addressed a rumor that RBR-TVBR heard regarding a rate reduction in The Detroit Pistons contract with Clear Channel’s Sports WDFN-AM 1130 kHz over poor reception in the evenings. Details had it that 50-kW KMOX St. Louis (1120) and 50-kW WRVA Richmond (1140) were killing WDFN’s nighttime signal because of their skywave HD Radio carriers on 1130... But he did note it was because of reception complaints: That was one of the components, and we were with them for five years. They had a weak signal and we were getting a lot of people that could not hear us. It could have been because of HD Radio, but at the time we were totally unaware of it."
"Could EXB Band Be Your New Home?"
"The group says most AMs should move to the new band, where they would operate as FMs on channels of 100 kHz width, enjoy more parity with current FM stations in terms of audio fidelity and gain the ability to go all-digital. AMs could transition to 100 channels and operate in the all-digital mode. In this way, AMs 'can solve the current digital problems they are experiencing, especially at night', the group states. But while most would move, the existing band could, under their plan, also remain populated with clear-channel stations that would enjoy more elbow room. Under the proposal, filed with the FCC in its diversity proceeding (Docket 07-294), the old AM band would be 're-packed.'"
"Lightning taking out AM IBOC"
"A live demonstration of how lightning affects an AM HD Radio signal with a relatively weak thunderstorm in progress judging by the infrequent lightning."