adjacent channel interference

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Until recently, to many in the industry, HD radio seemed to be an afterthought – maybe useful in feeding analog translators, but otherwise not very accessible to the public.  But there is now more and more interest in HD radio given the increased inclusion of receivers for this digital service as standard equipment in a majority of new cars.  This means that consumers have ready access to programming on digital FM subchannels that the technology allows, plus the digital sound quality that HD radio provides and the auxiliary data services that can be conveyed along with the audio programming.  This week, the FCC’s Media Bureau issued a Public Notice asking for comments on two technical proposals to enhance service to the public while minimizing interference that the service might otherwise cause to nearby adjacent-channel stations.

Comments are sought on a proposal by the National Association of Broadcasters and Xperi, Inc. (which acquired iBiquity, the company that developed the HD Radio technology) seeking adoption of an updated formula for computing the power level of the “sidebands” on which the HD service resides. The request also asks that the proposal be combined with a 2019 request that FM stations be allowed to operate an HD service with “asymmetric sidebands” without having to seek experimental authority.  What do these requests mean and why might they be important?
Continue Reading FCC Seeks Comments on HD Radio Technical Standards – Could a Power Increase for Digital FM Radio Be Coming?

When the Low Power FM service was first authorized, it was as a "secondary service," though a recent court decision shows how that secondary status is becoming less and less a reality.  A secondary service is traditionally one that can be allotted where there are no other uses for a particular frequency, and which is subject to being bumped off the spectrum should there be another demand for that spectrum by a "primary" user.  LPFM stations were originally supposed to provide service to areas between full-power FM radio stations, and to be bumped off the air if there was a new FM station authorized or a change in the frequency or power of an existing station.  A decision of the Court of Appeals released earlier this month , upholding an FCC order giving more protections to LPFM stations, puts this secondary service into question.

The Court decision upheld the Commission’s decision, about which we wrote here, determining that waivers of second adjacent channel interference limitations between LPFM and full power stations should be permitted to help preserve LPFM service.  In addition, the Court upheld the FCC’s process in adopting a new "interim" policy which provides that, where an LPFM is providing 8 hours a day of local programming and would be knocked off the air by an upgrade or city of license change of a full-power station, the LPFM station could apply for a waiver of its secondary status, and there would be a rebuttable presumption in favor of such a waiver.  If the waiver is granted, the LPFM station would be preserved, and the application of the full-power station dismissed.  Thus, effectively, LPFM would no longer be secondary, but instead will have assumed a primary, protected status.Continue Reading LPFM – When a Secondary Service Becomes Primary