73.809

Part 73, Subpart G, §73.809 is a regulation that addresses the procedures that would apply when a full-power FM station applies for a facility that would result in the LPFM station causing interference to the new or modified full-service FM facility. This is also known as "The Encroachment Rule". This rule also covers interference caused by an LPFM station to broadcast or non-broadcast services because of a faulty transmitter.

Interference due to a new or modified full-power FM facility

Secondary nature of LPFM service

Low power FM stations and FM translators are considered "secondary" services. Full-service (full-power) FM stations are considered as "primary". This means that a primary FM facility can request a facility without the need to protect any of the secondary facilities. Depending on the full-power station's new location, power and terrain, the LPFM station may experience no difference, a diminished service area in one portion of town or very substantial interference rendering the LPFM station useless. In addition, the operation of the LPFM station may create harmful interference to the new or modified full-power FM operation. The latter is where this rule comes into place.

How interference from the LPFM station is determined

Using broadcast planning software, the representative of the full power station will create a map showing the interfering contours of the LPFM station and comparing them with the service contours of the protected full-power FM facility.

Criteria for Interference

For full-power application activity, the FCC requires one of the following situations before it can force an LPFM station to shut down:

Community coverage contour interference

Actionable interference is deemed to take place if the 70 dBu community coverage contour of the full-service FM station (also known as the "city grade" contour) is overlapped by the 40 dBu interfering contour of the LPFM station operating on the same channel or the LPFM 54 dBu interfering contour on a first-adjacent channel.

Interference within the community of license

Actionable interference is deemed to take place if the LPFM's co-channel 40 dBu interfering contour overlaps into a portion of the community of license of the affected full-service FM station. If the LPFM is on a first adjacent channel, then it is the LPFM's 54 dBu interfering contour.

Contour overlap in the community community of license

Actionable interference is deemed to take place if the LPFM's co-channel 40 dBu interfering contour overlaps into the 60 dBu protected contour within the community of license of the affected full-service station. If the LPFM is on a first-adjacent channel, then its the LPFM's 54 dBu interfering contour.

Interference remediation process

If the contour study demonstrates that the LPFM station would be causing prohibited interference, the full-power station can file a complaint with the FCC Media Bureau and must serve a copy of the complaint to the LPFM station. Once the LPFM station receives the complaint (either from the FCC or from the affected full-power station), they are to cease operations (shut down) within 24 hours. The LPFM station must take measures to eliminate the interference. This could include changing to a different channel if another channel is available to move to.

The full-service FM broadcast station is required to cooperate with the LPFM station during the remediation process. If the FCC determines that the complaining station was not cooperative, then the FCC can absolve the LPFM station of the complaint.

Spurious Emissions

A properly designed and certified LPFM transmitter in good working order, will keep the signal on the LPFM station's assigned channel/frequency. Sometimes, due to either an issue with the transmitter or improper installation, the transmitter may also broadcast additional signals on undesired frequencies. This is known as spurious emissions (or "spurs"). Transmissions from spurs are not just limited to the FM broadcast band and over the years, there has been numerous reports that a defective transmitter will place a signal on a frequency in the spectrum adjacent to the FM band on frequencies that are used for aeronautical navigation or communications.

If the FCC notifies the LPFM station that their station is causing spurious emissions, it is very urgent that the LPFM transmitter be shut off immediately. There is no 24 hour waiting period as the transmissions may cause danger to the safety of life. During the time the station is suspended, it may make short test transmissions to test the repairs to the transmitter.

Post suspension report

If an LPFM station operation is resumed at the authority of the FCC for any interference reason, the LPFM needs to follow up with a report stating details of the interference, the source of the interference and what remedial actions took place.

Regulatory history

The original version of this rule was enacted in the LPFM Report and Order when the service was created in 2000. The rule at the time only considered interference to the full-service FM station's city grade contour and covered co-channel, first and second adjacent channels as well as intermediate frequencies (+/- 10.6 or 10.8 MHz). In the Order on Reconsideration from September, 2000, the FCC added the additional interference criteria to include the "Interference in the community of license" (for commercial stations) and the "contour overlap in the community of license" (for noncommercial stations) criteria. In the Third Report and Order, enacted in 2007, the distinctions between commercial and noncommercial were removed from the rule language. Criteria for displacement on second-adjacent channels were also eliminated. 2013, in the Sixth Report and Order, the FCC removed the criteria that intermediate frequency overlap would be considered as actionable interference.

Federal Register citation

65 FR 7640, Feb. 15, 2000, as amended at 65 FR 67302, Nov. 9, 2000; 73 FR 3216, Jan. 17, 2008; 78 FR 2104, Jan. 9, 2013

Text of regulation 47 CFR §73.809

§ 73.809 Interference protection to full service FM stations.

(a) If a full service commercial or NCE FM facility application is filed subsequent to the filing of an LPFM station facility application, such full service station is protected against any condition of interference to the direct reception of its signal that is caused by such LPFM station operating on the same channel or first-adjacent channel provided that the interference is predicted to occur and actually occurs within:

(1) The 3.16 mV/m (70 dBu) contour of such full service station;

(2) The community of license of such full service station; or

(3) Any area of the community of license of such full service station that is predicted to receive at least a 1 mV/m (60 dBu) signal. Predicted interference shall be calculated in accordance with the ratios set forth in § 73.215 paragraphs (a)(1) and (a)(2). Intermediate frequency (IF) channel interference overlap will be determined based upon overlap of the 91 dBu F(50,50) contours of the FM and LPFM stations. Actual interference will be considered to occur whenever reception of a regularly used signal is impaired by the signal radiated by the LPFM station.

(b) An LPFM station will be provided an opportunity to demonstrate in connection with the processing of the commercial or NCE FM application that interference as described in paragraph (a) of this section is unlikely. If the LPFM station fails to so demonstrate, it will be required to cease operations upon the commencement of program tests by the commercial or NCE FM station.

(c) Complaints of actual interference by an LPFM station subject to paragraphs (a) and (b) of this section must be served on the LPFM licensee and the Federal Communications Commission, attention Audio Services Division. The LPFM station must suspend operations within twenty-four hours of the receipt of such complaint unless the interference has been resolved to the satisfaction of the complainant on the basis of suitable techniques. An LPFM station may only resume operations at the direction of the Federal Communications Commission. If the Commission determines that the complainant has refused to permit the LPFM station to apply remedial techniques that demonstrably will eliminate the interference without impairment of the original reception, the licensee of the LPFM station is absolved of further responsibility for the complaint.

(d) It shall be the responsibility of the licensee of an LPFM station to correct any condition of interference that results from the radiation of radio frequency energy outside its assigned channel. Upon notice by the FCC to the station licensee or operator that such interference is caused by spurious emissions of the station, operation of the station shall be immediately suspended and not resumed until the interference has been eliminated. However, short test transmissions may be made during the period of suspended operation to check the efficacy of remedial measures.

(e) In each instance where suspension of operation is required, the licensee shall submit a full report to the FCC in Washington, DC, after operation is resumed, containing details of the nature of the interference, the source of the interfering signals, and the remedial steps taken to eliminate the interference.