IBOC is an acronym for In Band On Channel, which is a commercially 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, but sounds like a continuous loud 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 whole bandful of IBOC transmitters hasn't been experienced yet, but would be anticipated to be significant.

From the few stations it is on, DXers are on 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 still out as to the public acceptance of IBOC. Few receivers available as many were discontinued. Automotive companies are still adding that type of radio. Many AM stations have dropped IBOC, however.

Despite huge amounts of time and money spent by the proponents, HD Radio is stalled. There is a web site with blogs discussing that.

Blog Link

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.


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

Kahn filing

Comments on HD Radio, now that it is about to be turned loose on the North American listening public. The original comments are updated with a further thought or two.


Several comments about the HD Radio editorial challenged me to offer a viable alternative rather than just complain.


A good technical article on HD Radio digital sideband power has been added to the IBOC section to the left. Thanks to Clear Channel VP of Engineering Steve Davis for allowing us to post this.

Steve's article

Last update: 21 January 2012