An e-mail from ABC-Citadel corporate engineering has reportedly issued an order effective this morning to suspend AM In-band on-channel (IBOC) operations, according to Radio-Info.
The communication came from Citadel's Martin Stabbard, according to sources.
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.
IBOC is the method in which iBiquity utilizes to broadcast the HD Radio signal - using sidebands to transmit the digital data over AM/FM waves. But since wider channels are required, both the AM/FM implementations of the iBiquity system often cause interference with adjacent stations on the dial. As a result, lower power stations can become unlistenable if they have an HD Radio station on an adjacent channel.
UPDATE: Apparently Citadel/ABC's AM stations will suspend nighttime HD Radio transmission until they can do further work with iBiquity to reduce adjacent-channel interference. Radio-Info adds that, "the FCC allowed nighttime AM digital as of September 14 - and the complaints have mounted up."