A look at the footnotes in the FCC’s pending geotargeting rules shows how concerned the National Association of Broadcasters has been about the need to limit self-interference by adopting a uniform synchronization standard.
The draft of the FCC’s Second Report and Order on Reconsideration, released last week, would establish steps and procedures for broadcasters who want to use FM boosters to originate programming. The commission will vote on those final rules this month.
[“FCC Releases Details of Pending Geotargeting Rules”]
The NAB had proposed that carrier frequencies should be locked together using a common reference to reduce co-channel interference, according to the FCC’s summary. NAB proposed using GPS as a reference to ensure that carrier frequencies are synched.
But the FCC states in the draft that it chose not to include a uniform synchronization standard because “broadcasters have a strong economic incentive to synchronize in the manner most effective to their own particular location and system design in order to provide the best listener experience.”
Yet it also said the points that NAB made could be useful to broadcasters designing booster systems that will originate programming.
The details
GeoBroadcast Solutions, the developer of ZoneCasting, had asked the FCC not to develop or require specific synchronization standards. It believes broadcasters’ own on-site technical experts would be in a better position to determine the most effective way to synchronize under each broadcaster’s individual conditions.
GBS said FCC-mandated engineering standards for synchronization would be unnecessary and constitute time-consuming “micromanagement” of a highly technical and evolving process.
The FCC reviewed this issue in a section of the draft order dealing with synchronization and self-interference.
FM boosters are low-power, secondary stations that rebroadcast programming on the same frequency of a primary FM station, which brings the possibility of causing interference for listeners. The NAB argued that failure to maintain coherence between a main signal and program-originating booster carrier frequencies would cause incidental AM modulation or beating, which will manifest as “picket-fence” interference that would frustrate listeners.
The NAB wrote that synchronization involves several methodologies and proposed standards for each. The FCC devoted an extensive footnote to summarizing the NAB’s comments.
“With respect to synchronization of modulation parameters, NAB proposes that modulation levels, including peak deviation and stereo pilot frequency, should also be identical. (NAB) argues that studies show that even a small mismatch in composite baseband modulation levels, such as 0.5 dB, can dramatically increase perceived audio distortion when the signal levels of the booster and main transmitter are similar.”
Concerning synchronization based on program time delay, the NAB argued that time alignment of programming is critical in transition areas where the main and booster RF signal levels are approximately the same because rapid degradation in audio distortion occurs when the time misalignment exceeds 1 microsecond.
According to the summary, the NAB suggested that the alignment should be adjusted so that the program material received from the booster and main transmitters has no time delay in areas where the booster and main signal levels are within 10 dB.
The association recommended that stations be required to verify proper synchronization after a “crash” or when the system reboots for some reason because restarting a system may impact synchronization. And it suggested that broadcasters have a means for disabling the booster if it is not operating as designed.
But the FCC in its draft states that, because it is providing broadcasters the flexibility to design systems most suited to their circumstances and is not adopting a uniform synchronization standard, “we do not respond to each of these suggestions.” Yet it concluded that NAB’s concerns may be beneficial to the industry.
“We note NAB’s concerns may be useful to individual broadcasters and their consulting engineers in determining what synchronization parameters are most appropriate for the particular issues that may affect individual booster systems,” it said.
The FCC acknowledged that several commenters believe that program-originating boosters will increase interference between a broadcaster’s boosters and its primary station. Those commenters, including NPR, believe that self-interference could lead to a degradation of service and general confusion among listeners.
You can read the discussion and footnote on page 10 of the FCC’s draft order.
