Skip to main content

FCC Modifies Interference Analysis Program

Prior to the DTV transition a year ago, the FCC had said that it would protect television stations' DTV Allotment Appendix B facilities for approximately one year after the completion of the transition. That year has passed and late last week, the commission announced that it has revised the interference analysis program it uses for processing applications on TV frequencies to exclude Appendix B facilities from the analysis. Existing construction permits will continue to be protected and active applications should get protection from cut-off rules.

Stations that delayed filling for constructing facilities that matched or extended their Appendix B coverage may find they have difficulty expanding coverage in the future. Other full-power stations or Class-A TV stations looking for displacement channels in congested areas will likely take advantage of this loss of protection.

While the FCC will continue to use the DTV Allotment Table Appendix B for determining baseline service and interference populations, I wouldn't be surprised if the new analysis resets the baseline interference to Class A LPTV stations that accepted interference from a full power station to the interference from the currently authorized facilities, thus preventing any further coverage expansion by the full power station. If that is the case, it seems some existing applications, when processed, may fail an interference analysis.

Loss of interference “masking” from a DTV Appendix B allotment could also impact applications.

Stations that don't build out their authorized facilities could also lose protection. FCC TV construction permits are valid for three years. Stations that filed maximization applications before the FCC freeze and received construction permits in 2008 will see them expiring next year. There was a flood of maximization applications filed after the freeze ended June 20, 2009, and those will be expiring in 2012. Since the FCC does not allow a station to have two broadcast construction permits (CP) at the same time, if these facilities are not constructed before the CP expires, those stations will also lose interference protection. With the potential changes coming from the National Broadband Plan, it may be hard to spend money building out facilities on a channel that may be taken away. However, it only seems fair that stations with the largest coverage would have the best chance of maintaining it after any future channel reallocation.

As part of the change in the change in the FCC's interference analysis, the FCC will finally adopt the broader LPTV elevation pattern it announced a few years ago. The net effect of this change will be to increase predicted LPTV field strength inside the LPTV, translator or Class A station's contour. For existing authorizations, this could raise the interference to full-power stations above “de-minimis” levels. As with the changes in interference masking and protected coverage for full power stations, this could invalidate some applications currently on file with the FCC. However, the increased signal level will improve D/U (desired to undesired) interference ratios for interfering stations, offsetting some of the impact.

To summarize, these two changes in the FCC TV interference analysis software will have an impact on future applications, and might affect applications currently on file. If your station has any pending applications, it may be worth doing a new interference study to see if these changes caused any change in interference. If interference is now above “de-minimis” levels, amending it now to bring interference to an acceptable level should keep it from being rejected.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.