73.809 Interference protection to full service FM stations

This section outlines the rules on how a full power station can complain about interference by an LPFM station and what the FCC considers as legal interference. Legal interference can happen if after an application is filed by the full service station after the LPFM files their application, it is predicted to or to actually occur as follows:

  • If the full-service station's 70 dBu service contour overlaps the 40 dBu interfering contour of a co-channel LPFM station or the 54 dBu interfering contour of a first-adjacent channel LPFM station.
  • If the full-servcice sation is on the same channel as the LPFM, if the 40 dBu interfering contour overlaps the community of license for the full-service station. If the full-service station is on a first-adjacent channel, then if the 54 dBu interfering contour overlaps the community of license of the full-service station. (Noncommercial stations operating on 88.1~91.9 are only required to provide a 60 dBu service contour to at least 50% of the community of license.
  • If the community of license receives at least a 60 dB field strength from the LPFM station on the full-service station's channel or first adjacent channel. We interpret this rule to also include terrain-based propagation models such as Longley/Rice to make the showing. Contours do not always represent the actual field strength at a particular location due to terrain and other factors.
In response to a complaint, the LPFM can make a showing that despite the subsequent application, the LPFM station will not cause interference. If the LPFM station is unable to show that interference will not happen, the LPFM station will have to cease operation prior to the full-service station going on the air (program test).

The full-service station must send a complaint to both the LPFM station and to the FCC. The LPFM station will have to go off the air within 24 hours of receiving the complaint, even if the station does not receive any notification from the FCC.

The full-service station must cooperate with the LPFM station to resolve the interference. If the FCC determines that the full-service station refused to work with the LPFM station, then the LPFM station will be absolved from the interference and can continue to operate.

Spurious emission is when the transmitter also radiates on a different frequency. This type of interference could take place in the radio spectrum used by aviation. If the FCC notifies the LPFM that their station is causing spurious emissions, then the LPFM station must shut down immediately upon notification. The LPFM station can't resume until the problem is fixed. Short "on-off" tests can be made to verify that attempts to remove the spurious emissions have resulted in the elimination of that interference.

In any case of interference, the LPFM station must provide a full report to the FCC after the station goes back on the air. The report needs to include details of the interference, the source of the interference and what steps were made in order to fix the problem and eliminate the interference.

One of the other selling points of distance separation instead of contours is that because the FCC has called distance separation a "superior" form of spacing stations, whatever the reality of interference is in a certain situation is irrelevant if distance spacing comes into play. The FCC wanted to make sure that even if full-service stations moved, they wanted to assure that LPFM stations would not be needlessly impacted but a line must be drawn. This rule is that line. It limits interference in the commercial band (92.1~107.9) to situations where the interfering contour of the LPFM station overlaps the 70 dBu city-grade contour of the full-service station when that station has made a move. That's the only time a commercial band station could complain about an existing LPFM station. For non-commercial, the LPFM interfering contour can't overlap the community of license of the moving full-service station.

Also note, there is a companion rule ง73.209(c) which states that a full-service FM station is not protected from subsequent LPFM application activity as long as the LPFM station meets minimum distance separation requirements.

Text of Current Rule

(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 caused by such LPFM station that operates 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 subsections (a) and (b) 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, D.C., 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.

Rule History

ยง 73.809 Interference protection to full service FM stations.

(a) It shall be the responsibility of the licensee of an LPFM station to correct at its expense any condition of interference to the direct reception of the signal of any subsequently authorized commercial or NCE FM station that operates on the same channel, first-adjacent channel, secondadjacent channel or intermediate frequency (IF) channels as the LPFM station, where interference is predicted to occur and actually occurs within the 3.16 mV/m (70 dBu) contour of such stations. Predicted interference within this contour shall be calculated in accordance with the ratios set forth in ยง 73.215(a)(1) and (2) of this part. Actual interference will be considered to occur whenever reception of a regularly used signal is impaired by the signals radiated by the LPFM station.

(b) An LPFM station will be provided an opportunity to demonstrate in connection with the procession of the commercial or NCE FM application that interference with the 3.16 mV/m contour of such station 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 paragraph (b) within the 3.16 mV/m contour of a commercial or NCE FM station 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.

(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.

65 FR 7640 (Feb 15, 2000).

ยง 73.809 Interference protection to full service FM stations.

(a) It shall be the responsibility of the licensee of an LPFM station to correct at its expense any condition of interference to the direct reception of the signal of any subsequently authorized commercial or NCE FM station that operates on the same channel, first-adjacent channel, second adjacent channel or intermediate frequency (IF) channels as the LPFM station, where interference is predicted to occur and actually occurs within: the 3.16 mV/m (70 dBu) contour of such stations. Predicted interference within this contour shall be calculated in accordance with the ratios set forth in ยง 73.215(a)(1) and (2) of this part. Actual interference will be considered to occur whenever reception of a regularly used signal is impaired by the signals radiated by the LPFM station.

(1) The 3.16 mV/m (70 dBu) contour of such stations;

(2) The community of license of a commercial FM station; or

(3) Any area of the community of license of an NCE FM 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 ยงยง 73.215(a)(1) and 73.215(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 signals radiated by the LPFM station.

(b) An LPFM station will be provided an opportunity to demonstrate in connection with the procession of the commercial or NCE FM application that interference with the 3.16 mV/m contour of such station 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 paragraph paragraphs (a) and (b) within the 3.16 mV/m contour of a commercial or NCE FM station 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.

65 FR 67302 (Nov 9, 2000).

ยง 73.809 Interference protection to full service FM stations.

(a) It shall be the responsibility of the licensee of an LPFM station to correct at its expense any condition of interference to the direct reception of the signal of any subsequently authorized commercial or NCE FM 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 caused by such LPFM station that operates on the same channel, first-adjacent channel, second adjacent channel or intermediate frequency (IF) channels as the LPFM or to such full service station, where provided that the interference is predicted to occur and actually occurs within: 

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

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

(3) Any area of the community of license of an NCE FM 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 ยงยง 73.215(a)(1) and 73.215(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 signals radiated by the LPFM station.

(b) An LPFM station will be provided an opportunity to demonstrate in connection with the procession 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.

73 FR 3216 (Jan 17, 2008)

ยง 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 caused by such LPFM station that operates operating on the same channel, or first-adjacent channel or intermediate frequency (IF) channels as or to such full service station, 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 ยงยง 73.215(a)(1) and 73.215(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 signals 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.

78 FR 2104 (Jan 9, 2013)