IBOC Info

IBOC is an acronym for In Band On Channel, which is a newly introduced method for radio stations to broadcast in a digital format. There are versions for both AM and FM. We'll concern ourselves with the AM type. The program content is digitized to a common format such as AES/EBU. It is processed as desired to even off the high and low volume parts (compression and limiting). It is then sent to a modulator device. This device takes the digital information and creates data sidebands which are applied to a wideband AM transmitter. These sidebands go out roughly 15kHz above and below the center frequency. If a station on 710kHz broadcasts IBOC information, it will be audible on both 700 and 720kHz. It sounds like a continuous hiss, For station owners, this may have some advantages such as better fidelity, and the ability to send text and data information that is not currently possible. The interference of a bandful of IBOC transmitters hasn't been experienced yet, but it is anticipated to be significant. From limited testing at WLW-700 and WOR-710 it appears that DXers will be in for a rough ride. There have been reports that the IBOC hiss can be heard further than the analog audio. The hiss has been reported in Arizona, yet the station that sent it was not detectable by any other means. The jury is likewise out as to the public acceptance of IBOC. If the experience of XM and Sirius satellite radio is any indicator, it may be years before there is any significant listenership.

Here is a PDF file of a great description of IBOC aka HD Radio written by Chip Morgan of CMBE. It's written from the perspective of a broadcaster, and not a DXer. It does include some FM info which may be useful for reference. HD Radio Primer

Here is a fairly large (250k) PDF of the Clear Channel IBOC testing in Washington,DC. Shows some significant interference potential. Clear Channel Report

Current FCC Notice of Proposed Rulemaking and Notice of Inquiry on IBOC in PDF format. Released 20 April 2004. FCC NPRM/NOI

Filing by Leonard Kahn on IBOC and why he feels it shouldn't be allowed. PDF format, almost 500kb. Kahn filing

Calculations of AM HD Radio Digital Carrier Power by Steve Davis, VP Engineering for Clear Channel. Posted by permission, and with our thanks! Steve's article