FCC Examines Repacking Station Interference Issues

While there are still some serious questions surrounding the incentive auction (such as whether the industry can make all the required channel changes within the 36 months allotted, and how well the TVStudy parameters will work), I have to give the FCC staff credit for taking the effort to make sure broadcasters that don't choose to participate in the auction are protected.

This extends to the use of a domain file to determine what channels are available to a station and an interference-paired file defining which pairs of stations that cannot operate co-channel, upper-adjacent channel, or lower-adjacent channel to each other should ensure that stations changing channels within a band maintain their existing coverage.

One of the major criticisms of the use of these constraint files was that they were to be based on proxy channels. The FCC staff has determined that they are now able to generate these constraint files based on actual channels rather than proxy channels.

The FCC Appendix: Analysis of Potential Aggregate Interference analyzing the impact of this approach on the amount of interference TV stations would receive as a result of the repacking. The analysis showed the amount of aggregate new interference under three different scenarios assuming 80, 90 or 100 percent participation in the auction and a clearing target of 84 MHz or 120 MHz. Stations that failed the "feasibility check" were determined to be "off-air" (their bid accepted) and interference was calculated for the remaining stations, including the 10 or 20 percent not participating in the auction. Three methods were used to determine the order in which stations were analyzed: Population, Population/Blocked Channels, and DMA rank.

Constraint files limit interference from one station to another to 0.5 percent, so this analysis examines aggregate interference. The good news is that only one percent of the stations are predicted to receive new aggregate interference after repacking (above the NAB's proposed one percent cap), while the average new aggregate interference level was less than 0.2 percent. None of studies showed any station receiving new aggregate interference greater than two percent.

Refer to the Appendix for details on how the study was conducted. It seems unlikely actual auction participation will match the 100-, 90-, or even the 80-percent number used in the analysis. In this case, using such high participation numbers could be considered "worst case," but it's also possible that some of the stations considered to be "off-air" in the auction might decide not to participate and perhaps pose problems for the repacking.

The Public Notice announcing the analysis cautioned, "As noted in prior Public Notices, the data and information released today are based on preliminary assumptions necessary for completing the analysis, and are illustrative only. The Commission will adopt final decisions regarding the repacking process at a later date."

Links to the constraint files are available from the FCC Constraint Files for Repacking webpage.

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. As vice president of Broadcast Technology for NBCUniversal Local, H. Douglas Lung leads NBC and Telemundo-owned stations’ RF and transmission affairs, including microwave, radars, satellite uplinks, and FCC technical filings. Beginning his career in 1976 at KSCI in Los Angeles, Lung has nearly 50 years of experience in broadcast television engineering. Beginning in 1985, he led the engineering department for what was to become the Telemundo network and station group, assisting in the design, construction and installation of the company’s broadcast and cable facilities. Other projects include work on the launch of Hawaii’s first UHF TV station, the rollout and testing of the ATSC mobile-handheld standard, and software development related to the incentive auction TV spectrum repack. A longtime columnist for TV Technology, Doug is also a regular contributor to IEEE Broadcast Technology. He is the recipient of the 2023 NAB Television Engineering Award. He also received a Tech Leadership Award from TV Tech publisher Future plc in 2021 and is a member of the IEEE Broadcast Technology Society and the Society of Broadcast Engineers.