The FCC has proposed loosening the principal community coverage rule for AM stations. This is part of the new Notice of Proposed Rulemaking MB Docket 13-249.
Commissioner Pai should be commended for pressing forward on this, as it is a major difficulty for AM stations that lose their site. Unfortunately, the proposal remains mired in historical thinking and does not resolve the root problem.
The rulemaking proposes that applications for new and principal community changes maintain the requirement that 80% of the principal community be covered by the Night Interference Free contour (or the 5 mV/m contour if the station is fortunate enough to have a low limit). Minor change applications would be subject to a more generous limit of 50% of the principal community. The reason that many AM stations seek principal community changes is because the old site is no longer available to the station, and no other available site can provide coverage of the old principal community. Unfortunately the relief proposed is too modest to solve the problem.
Night Interference Free contours are so high for many stations that it is difficult to get enough NIF service area to cover any entire community. This coupled with the requirements to protect other stations (which limits signals in many directions) make relocating night antennas particularly problematic. This is particularly awkward since many cities have annexed additional land area, and merged communities – doubling or tripling the original city area.
Class C AM stations (local channel), for example, often cannot meet even the proposed minor change requirement of 50% of principal community coverage requirement with the transmitter located at very center of the community. Class C stations are not protected from skywave interference, so their NIF contours are determined by other stations and subject to change. I believe that night principal community coverage requirements for class C AM stations should be deleted.
The NIF contour is the signal level where no substantial interference is received by the station in the middle of the night. In the morning and evening “drive times”, and early evening hours interference is much less severe than in the middle of the night, particularly at the low end of the band. The night service is of substantial value to the community even if the signal does not cover everywhere at midnight.
Applications to move AM stations also suffer from the problem that it is often impossible to relocate the original stations four to six tower arrays because of the amount of land needed is simply not available in a single plot. Another limitation often is the non-optimal arrangement of towers when a station is added to combined transmitting facilities on one site.
Where a station previously had five to fifty kilowatts available at night and six towers, a two or three tower sub-optimal antenna that may be all that is possible, The maximum night power without causing interference might be only one or two kilowatts, making night principal community coverage even more problematic.
I propose that the FCC consider that for all changes where the licensed and proposed day 5.0 mV/m service areas overlap, that night principal community contours should be based upon the 5.0 mV/m contour and ignore the NIF. New stations and major changes (out of market) could require NIF coverage because the demand for new AM stations is low.
I agree that a 50% coverage requirement is reasonable for minor changes, provided that it is based upon the 5.0 mV/m contour. There should also be a standard that an application for changes should not need to provide any greater percentage coverage to the principal community than from the licensed facility. Many applications have taken more time to process and consumed more commission resources because a waiver was needed even though the application improved deficient coverage of a community. This was because the coverage remained below the threshold requirement.
Another possible “fix” to the loss of site scenario would be to permit AM minor change applications to convert from class B to class D while maintaining a night power not exceeding the licensed night power. The station would still be required to protect other stations, but it would no longer be protected from interference, and it would have no principal community contour coverage requirements.