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Update on LPFM Rules
These two, however, are not the only provisions that follow from the implementation of the Act. The LCRA explicitly grants the Commission the authority to waive second-adjacent spacing requirements. Under the relevant section of the Act, this waiver is permissible in instances where an LPFM station establishes that no interference is predicted to occur to any authorized service by taking into account all relevant factors including terrain-sensitive propagation models. On the translator side the Commission has routinely allowed specific studies demonstrating that zero population would be affected by an interference area although an interference area may nevertheless exist. The wording of the statute is such that the Commission has sought additional comment on how to implement this portion of it.
In addition, the Commission is also required to modify the current rules to address predicted interference to FM translator input signals on third-adjacent channels. This requirement makes sense. In many cases translators are employed to provide reception of full power FM facilities when not technically feasible As a result, the signals received by the translator, tend to be somewhat weak, and become usable through amplification either by antennas or active device. It is plausible that a co-located LPFM could desensitize the receiver of an FM translator receiving its material off-air. At present the Commission requires LPFM stations to remediate actual interference to FM translator input signals, but had not codified spacing requirements or other measures. Because of the statute language requiring the Commission to address predicted interference, it has been concluded that the subjective provision must be more strongly established.
The current proposal is to track the Mitre standard. Under this proposal, the Commission is proposing that any application for a new or modified LPFM station not use a transmitter site within a potential interference area. This potential area is defined as any location within 2km of the translator site or any area within 10km of the translator site within azimuth of 30 degrees either side of the direct bearing between the translator and the source of the received signal.
If a proposed LPFM were to be located in one of those areas, then the Commission is proposing that a demonstration of lack of interference be made through one of two methods. First the applicant may show that the ratio of the signal strength of the LPFM signal to the translator signal is below 34dB at all locations. Alternately the equation in the Mitre report may be used. This equation computes a separation distance based on the ERP of the LPFM station, the gains of the translator antenna in the direction of the received signal and in the direction of the LPFM signal, and the predicted field strength of the desired signal at the translator site.
Moving out of the technical realm the Commission is considering eliminating the LP10 class of service, and implementing an LP250 class. To date there have been no LP10 facilities authorized, thus the elimination likely makes sense. The 250W class also seems to make sense, especially in rural areas. LPFM facilities in such an environment are plagued with viability concerns due to the population density.
Other proposed changes would correct rule wording to ensure that an LPFM applicant is community based, expand the commitment to serve Native Nations, relax the cross-ownership requirements, and permit Native Nations multiple ownership. Each of these proposed changes would likely serve to further foster the growth and continued viability of the LPFM service.
The upcoming LPFM window, which is likely still a year or two out, may represent one of the last opportunities for expansion of this service due to the finite nature of available spectrum. The proposed changes in the rules and procedures mandated by Congress, and implemented by the Commission, will seek to ensure that all secondary services get a shot at serving the local community.
Ruck is the principal engineer of Jeremy Ruck and Associates, Canton, IL.
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