The National Radio Standards Committee (NRSC) has added their latest set of guidelines relating to FM IBOC digital operations to their website, along with a new calculator application designed with the help of consulting engineers Cavell & Mertz.
NRSC-G202 - FM IBOC Total Digital Sideband Power for Various Configurations is a document specifically intended to help broadcast engineers establish total digital power and sideband levels for various modes of FM IBOC digital hybrid operation, using either symmetrical or asymmetrical sideband methodologies. The guideline complements NRSC-G201-A, a previous specification establishing specifications for determining the occupied bandwidth of FM IBOC digital hybrid and extended hybrid signals.
Included on the NRSC Web page is an online calculator application that allows users to enter specific information regarding their station's service mode and desired symmetrical or asymmetrical digital carrier levels, and then computes the total percentage of digital power required to achieve them.
Asymmetrical sideband operation has been proposed as a way of mitigating interference from higher-power IBOC digital sidebands to closely spaced first-adjacent channel stations, and is currently undergoing trials at NPR member station WAMU in Washington.