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Here’s What’s in the FCC Draft on Digital Power Levels

The issue will be taken up in August but don't expect final action that day

Here are more details about what the FCC will vote on in August regarding HD Radio FM power levels.

As we reported last week, the commission in August will consider an order and Notice of Proposed Rulemaking involving two technical proposals. It will not give a final approval to either proposal at that meeting, but a yes vote will indicate tentative approval and ask for public comment.

It would ask whether it should 1) change the methodology used by digital FM stations to determine if they are eligible to increase digital FM power up to –10 dBc, or 10% of analog power; 2) allow such power increases without the need for additional individual special authorization, but upon basic notification to the commission; and 3) allow digital FM stations to notify the commission of a power increase up to –10 dBc, using the notification procedures currently used for digital operation.

Proponents say that station conversions to digital have not kept up with the penetration of digital FM receivers, especially in automobiles. They believe that a big reason is the difficulty of replicating an FM station’s analog signal using currently allowable digital FM power levels.

The draft also will ask whether the FCC should grant blanket authorization to digital FM stations to originate digital transmissions at different “asymmetric” power levels on the upper and lower digital sidebands without having to request experimental authorization, but instead by filing a notification with the commission.

NAB, Xperi and NPR would like a given digital FM station to have the option to protect one adjacent analog FM station while increasing power on the other sideband frequency to expand its digital coverage and building penetration. They believe many more digital FMs could increase power above –14 dBc on at least one sideband. Out of 10,875 digital FM stations they studied, they contend that 6,120 could increase power to –10 dBc under the current rules, whereas if asymmetric sidebands were allowed, an additional 3,496 stations could increase one sideband to –10 dBc, with another 532 being able to increase one sideband’s power to between –14 and –10 dBc.

The FCC also will ask whether an FM station increasing digital power or implementing asymmetric sideband operation should be required to directly notify first-adjacent channel FM stations of these actions, or whether filing notification with the commission is sufficient.

Last, it will ask whether its existing interference mitigation and remediation procedures are sufficient to manage any reports of inter-station interference as a result of increased digital FM power or asymmetric sideband operation.

The draft document provides a useful history of digital FM power limits and of the discussion over asynchronous operation, as well as a summary of comments, concerns and objections raised by various parties such as NPR, REC Networks, engineer Aaron Read, the International Association of Audio Information Services and other radio industry stakeholders.

You can read the full draft proposal here in PDF form. Page 5 of that document provides a proposed updated table for determining maximum permissible FM Digital ERP.

The draft would limit the digital ERP of “superpowered” FMs to their class maximums; superpowered FM seeking to increase digital power above –14 dBc would still need experimental or special temporary authorization.

One key question is whether changing the power increase methodology will create “an unacceptable risk” of interference to adjacent-channel stations. The FCC noted that most commenters have agreed that interference would not be an issue, though some expressed caution about digital interference to FM analog stations, especially smaller stations.

Some worry about the possible impact on Class A FM stations, LPFM station and FM translators. The draft order says the FCC has received few interference complaints from full-service analog FM stations resulting from adjacent-channel digital transmissions. But it notes that secondary services like LPFMs and translators are not protected from interference from full-service stations, and it doesn’t propose to change that.

The order also would reiterate that the FCC initiated its process of authorizing digital broadcast operations in 1999 “with the eventual goal of moving terrestrial broadcasting from an all-analog to an all-digital world.”

Although it says it has no timetable for that migration, “our objective remains to advance the progress of digital radio without causing harmful interference or disruption to existing analog operations. This is especially true given the record evidence of increased digital FM receiver penetration, even though we recognize that such receivers are far from ubiquitous, and that the record is less complete with regard to non-automotive digital FM receiver penetration.

“It is this desire to encourage continued adoption of digital FM broadcast technology that informs our tentative conclusions and proposals in this NPRM.”

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